crxx

Ransomware Profile: crxx
Community-first incident guide – v1.1 (kept concise but actionable)

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Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmed extension: .crxx
• Renaming convention: Original files receive a double extension:
  originalname.ext.id-<UUID>[email protected]
  The UUID is 8-4-4-12 chars. In infections observed so far, the attacker e-mail placeholder is [email protected], [email protected], or [email protected].

2. Detection & Outbreak Timeline

• First public sighting: 2024-08-21 – infections peaked during the first half of September 2024.
• Primary clusters: Western Europe (ES, IT, FR) followed by LATAM and Australia, aligned with phishing waves in English and Spanish.

3. Primary Attack Vectors

• Exploitation:
  • Double-extortion phishing (pdf → js → Cobalt Strike → crxx payload).
  • Exploits targeting Ivanti EPM CVE-2024-29824 on port 20205/tcp to drop a WMI scheduled task.
• Lateral Movement:
  • Uses a built-in mini-EternalBlue clone (likely leaked from the 2021 Conti dump) on port 445/SMB if the endpoint is not dual-homed VLAN.
  • RDP brute force via Zerologon stripped credentials; only when lateral SMB fails.
• Auxiliary tools: Mini-NGrok reverse tunnels, SystemBC proxy for outbound Tor.

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Remediation & Recovery Strategies

1. Prevention

• Patch aggressively – the current kill chain relies almost entirely on CVE-2024-29824 (Ivanti) and SMBv1/EternalBlue.
• Segment networks – isolate VLANs at 445/139/135/20205; disable SMBv1 via GPO.
• Block outbound Tor/SSH at your edge firewall (default-drop TCP 9050/9001/22).
• Deploy AppLocker or equivalent protection to disallow unsigned .exe/.dll in user-writable locations.
• Back-up 3-2-1 rule – real-time backup plus an offline + cloud copy; crxx can reach all connected drives including .VHD, OneDrive sync folders.

2. Removal

1. Isolate immediately – disconnect network, disable Wi-Fi/Bluetooth.
2. Identify persistence – look for tasks named UpdaterService, SystemUpdate32, or random GUID in \Tasks\.
3. Terminate malicious processes:
   • wscript.exe (embedded JS),
   • rundll32.exe loading C:\Users\Public\crxx.dll,
   • reboothelper.exe that performs safe-mode restart.
4. Run official MSERT or Windows Defender Offline (update signatures to build 1.403.1235).
5. Remove residual registry keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run`CrUpdater`).
6. Verify rev – hash-check OS %windir% files; crxx overwrites defender\MpCmdRun.exe with a stub that disables scans.

3. File Decryption & Recovery

• Possibility to decrypt: Currently partial –
  • Kaspersky Rescue Tool v21.1.10.0 includes a crxx-crypt plugin (released 2024-11-25) that works if the victim ID contains “-D” suffix.
  • Avast Decryptor updated 2024-12-01 now recovers files ≤ 200 MB using leaked RSA-key1 and bruteforced AES-RNG weakness seen on 2024-10 builds.
• No public universal decryptor for later variants (AES-256 in GCM mode). This is why backup restoration remains the only failsafe.

Essential tools to deploy:

• Offline installer: IvantiEPM-CVE-2024-29824.msp
• SMB-v1 disable script: disable_smb1.reg (Microsoft-signed).
• Portable executable whitelist: MicrOS’ SignTool + EFS backup prior to infection (mounted shadowcopy extraction possible).

4. Other Critical Information

• Unique traits:
  • crxx introduces a bypass of Windows Restart Manager APIs (subtask safewriter.exe) before encryption – locks files without showing in handle.exe.
  • During encryption, it issues fsutil usn deletejournal /D C: to shred NTFS USN logs, erasing forensic breadcrumbs.
• Wider impact: Anaonymous crxx-as-a-service operation – multiple affiliate groups share one backend, so ransom notes differ but the decryptor is the same. No double-encryption observed (avoids victims paying twice).

EternalBlue still surfaces as the #2 infection vector, not an ancient myth!