CobaltStrike4.X之去除CheckSum8特征
VSole2021-11-17 14:09:10
NO.1 前言
之前介紹了CobaltStrike4.3的License認證分析，今天介紹一下CobaltStrike4.3去除CheckSum8特征的方法，CheckSum8的特征和具體算法不在此細說，但為了避免被掃描出來還是有必要進行修改的。
NO.2 代碼修改
BeaconPayload中修改異或數值為新：
隨便一個10進制數字即可，后面dll中改成對應的16進制數字。
NO.3 dll修改
使用CrackSleeve將dll進行解密:
https://github.com/ca3tie1/CrackSleeve/
1、將cobaltstrike.jar和CrackSleeve.java放一起
2、編譯(javac -encoding UTF-8 -classpath cobaltstrike.jar CrackSleeve.java)
3、解密文件(java -classpath cobaltstrike.jar;./ CrackSleeve decode) # windows命令行執行
Alt+T進行關鍵字搜索：2Eh
先雙擊再空格。直接修改xor的值，先Change byte找到2E修改，再Apply pathes to input file保存。（別忘記保存）
需要修改的dll：beacon.dll、beacon.x64.dll、dnsb.dll、dnsb.x64.dll、pivot.dll、pivot.x64.dll、extc2.dll、extc2.x64.dll
再加密dll，工具給的命令在我這輸入CustomizeString報錯了，于是給CustomizeKey寫到代碼里了，改完如下可用：
import common.*;import dns.SleeveSecurity;import java.io.*;import java.util.Enumeration;import java.util.jar.JarEntry;import java.util.jar.JarFile;
public class CrackSleeve { private static byte[] OriginKey = {58, 68, 37, 73, 15, 56, -102, -18, -61, 18, -67, -41, 88, -83, 43, -103}; private static byte[] CustomizeKey; //private static byte[] CustomizeKey = {58, 68, 37, 73, 15, 56, -102, -18, -61, 18, -67, -41, 88, -83, 43, -103};
private String DecDir = "Resource/Decode/sleeve"; private String EncDir = "Resource/Encode/sleeve";
public static void main(String[] args) throws IOException { if (args.length == 0 || args[0].equals("-h") || args[0].equals("--help")) { System.out.println("UseAge: CrackSleeve OPTION [key]"); System.out.println("Options:"); System.out.println("\tdecode\t\tDecode sleeve files"); System.out.println("\tencode\t\tEncode sleeve files"); System.out.println("\tkey\t\tCustomize key string for encode sleeve files"); System.exit(0); } String option = args[0]; if (option.toLowerCase().equals("encode")) { CustomizeKey = new byte[]{58, 68, 37, 73, 15, 56, -102, -18, -61, 18, -67, -41, 88, -83, 43, -103}; }
CrackSleeve Cracker = new CrackSleeve(); // 使用正版key初始化SleeveSecurity中的key if (option.equals("decode")){ CrackSleevedResource.Setup(OriginKey); Cracker.DecodeFile(); }else if (option.equals("encode")){ CrackSleevedResource.Setup(CustomizeKey); Cracker.EncodeFile(); } }
private void DecodeFile() throws IOException { // 文件保存目錄 File saveDir = new File(this.DecDir); if (!saveDir.isDirectory()) saveDir.mkdirs();
// 獲取jar文件中sleeve文件夾下的文件列表 try { String path = this.getClass().getClassLoader().getResource("sleeve").getPath(); String jarPath = path.substring(5,path.indexOf("!/")); Enumeration<JarEntry> jarEnum = new JarFile(new File(jarPath)).entries(); while (jarEnum.hasMoreElements()) { JarEntry Element = jarEnum.nextElement(); String FileName = Element.getName(); if (FileName.indexOf("sleeve")>=0 && !FileName.equals("sleeve/")) { System.out.print("[+] Decoding "+FileName+"......"); byte[] decBytes = CrackSleevedResource.DecodeResource(FileName); if (decBytes.length > 0) { System.out.println("Done."); CommonUtils.writeToFile(new File(saveDir,"../"+FileName),decBytes); } else System.out.println("Fail."); } } } catch (IOException e) { e.printStackTrace(); }
}
private void EncodeFile(){ // 文件保存目錄 File saveDir = new File(this.EncDir); if (!saveDir.isDirectory()) saveDir.mkdirs();
// 獲取解密文件列表 File decDir = new File(this.DecDir); File[] decFiles = decDir.listFiles(); if (decFiles.length == 0) { System.out.println("[-] There's no file to encode, please decode first."); System.exit(0); }
for (File file : decFiles){ String filename = decDir.getPath()+"/"+file.getName(); System.out.print("[+] Encoding " + file.getName() + "......"); byte[] encBytes = CrackSleevedResource.EncodeResource(filename); if (encBytes.length > 0) { System.out.println("Done."); CommonUtils.writeToFile(new File(saveDir,file.getName()),encBytes); } else System.out.println("Fail."); } }}
class CrackSleevedResource{ private static CrackSleevedResource singleton;
private SleeveSecurity data = new SleeveSecurity();
public static void Setup(byte[] paramArrayOfbyte) { // singleton = new CrackSleevedResource(paramArrayOfbyte); singleton = new CrackSleevedResource(paramArrayOfbyte); }
public static byte[] DecodeResource(String paramString) { return singleton._DecodeResource(paramString); }
public static byte[] EncodeResource(String paramString) { return singleton._EncodeResource(paramString); }
private CrackSleevedResource(byte[] paramArrayOfbyte) { this.data.registerKey(paramArrayOfbyte); }
private byte[] _DecodeResource(String paramString) { byte[] arrayOfByte1 = CommonUtils.readResource(paramString); if (arrayOfByte1.length > 0) { long l = System.currentTimeMillis(); return this.data.decrypt(arrayOfByte1); } byte[] arrayOfByte2 = CommonUtils.readResource(paramString); if (arrayOfByte2.length == 0) { CommonUtils.print_error("Could not find sleeved resource: " + paramString + " [ERROR]"); } else { CommonUtils.print_stat("Used internal resource: " + paramString); } return arrayOfByte2; }
private byte[] _EncodeResource(String paramString){ try { File fileResource = new File(paramString); InputStream fileStream = new FileInputStream(fileResource); if (fileStream != null) { byte[] fileBytes = CommonUtils.readAll(fileStream); if (fileBytes.length > 0) { byte[] fileEncBytes = this.data.encrypt(fileBytes); return fileEncBytes; } } } catch (FileNotFoundException e) { e.printStackTrace(); } return null; }}
命令重新加密dll：（解密加密其他版本cs修改為對應的OriginKey、CustomizeKey即可）
java -classpath cobaltstrike.jar;./ CrackSleeve encode
key的值從16進制到byte型轉換可用代碼：
import java.util.Arrays;
public class authTest { public byte[] intToByteArray(int num){ return new byte[] { (byte) ((num >> 24) & 0xFF), (byte) ((num >> 16) & 0xFF), (byte) ((num >> 8) & 0xFF), (byte) (num & 0xFF) }; } public static byte[] hex2bytes(String s) { int len = s.length(); byte[] data = new byte[len / 2]; for (int i = 0; i < len; i += 2) { data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16)); } return data;}
public static void main(String[] args){ authTest authTest = new authTest(); int header = -889274157; int num = 29999999; int watermark = 1;
byte[] bheader = authTest.intToByteArray(header); byte[] bnum = authTest.intToByteArray(num); byte[] bwatermark = authTest.intToByteArray(watermark);// System.out.print(Arrays.toString(bheader)+'\n');// System.out.print(Arrays.toString(bnum)+'\n');// System.out.print(Arrays.toString(bwatermark)+'\n'); System.out.println(Arrays.toString(hex2bytes("3a4425490f389aeec312bdd758ad2b99")));
}}
最后，把encode目錄下的dll，放到idea項目目錄中重新編譯打包。
進行測試uri地址雖說仍舊可以請求到，但內容已經無法用nmap腳本解密出來，同理也可躲避掃描：
除了修改異或值的方式，也可以用Beacon Stager listener 去特征的方式改掉checksum8算法，但是只能固定url訪問了，需要配合profile才能使用。
VSole
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