cl0p

[Content by Gemini 2.5]

cl0p Ransomware Community Resource

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cl0p
  • Renaming Convention:
    – The malware simply appends .cl0p to the original file name.
    – Example: Quarterly_Financial_Report.xlsx becomes Quarterly_Financial_Report.xlsx.cl0p.
    – No base-name changes, random characters, serial numbers, or email prefixes are introduced.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First samples observed in mid-February 2019.
    – Large-scale waves recorded in March 2021 (exploited Accellion FTA 0-days), December 2022–early 2023 (GoAnywhere MFT exploitation), and continuous activity through 2024 leveraging MOVEit Transfer vulnerabilities (May–July 2024).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Web-facing application exploits (most common):
    – CVE-2023-34362, CVE-2023-35036, CVE-2023-35708 (MOVEit Transfer)
    – CVE-2021-27101 … CVE-2021-27104 (Accellion FTA)
    – CVE-2023-0669 (GoAnywhere MFT RCE)
  2. Remote Desktop Protocol (RDP) brute force or compromised credentials for initial foothold, followed by lateral movement via Cobalt Strike/ TRUEBOT.
  3. Phishing Emails with password-protected ZIP archives dropping .ps1 or .lnk loaders.
  4. Software supply-chain hits: Trojanized 3rd-party installer files (rare but documented).

Remediation & Recovery Strategies

1. Prevention

  • Immediate patching:
    – MoveIt/Accellion/GoAnywhere: Deploy vendor patches listed above within hours of release—cl0p is notorious for same-day mass exploitation.
  • Segment web-facing DMZ infrastructure from internal storage (block SQL + SMB outward).
  • Disable SMBv1 across estate; install Microsoft KB5010790 et al. to prevent any legacy lateral-vector reuse.
  • Restrict RDP to VPN/IP-whitelisting + MFA; enforce “high-entropy mandatory passwords” policy.
  • Deploy EDR with behavioral detections for Cobalt Strike / TRUEBOT beacons (YARA rules for cl0p_* signatures are public in GITHUB sentinel-one/cl0p-detection).
  • Email-gateway sandboxing for ZIP, ISO, IMG attachments; quarantine macros and HTA files by default.

2. Removal

Post-detection incident logic (tested on Windows & Linux victims):

  1. Isolate Hosts
  • Physically disconnect network cables or VLAN quarantine.
  1. Kill Malicious Processes
  • Windows: taskkill /F /IM dump.exe (TRUEBOT) and taskkill /F /IM cl0p.exe; also spawn termination for rundll32.exe spawned from \AppData\Local\Temp.
  • Linux: kill -9 <pid> of the ELF dropper (often named kpid or cl0p).
  1. Delete Scheduled Tasks / Cron Jobs
  • Windows: schtasks /Delete /TN "SystemUpdate" /F (common cl0p persistence task).
  • Linux: crontab -r for user-level persistence; check /etc/cron.d/.
  1. Eradicate Artefacts
  • Delete %LOCALAPPDATA%\cl0p.exe and registry run keys under HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
  • Linux: rm -rf /tmp/.cl0p folder and startup script /etc/init.d/cl0psvc.
  1. Rescan with updated Defender / ClamAV signatures; run full EDR sweep for residual Cobalt Strike beacons.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – No free decryption is currently possible. Files are encrypted with a unique AES-256 key per file, in turn encrypted with an RSA-1024 public key tied to the attacker.
  • Essential Tools / Patches:
    – Backup Validation Utility (Veeam Secure-Restore, Druva, Zerto) to scan restore points for additional implants before reinstatement.
    – Offline/offsite immutable backups protected with MFA and network-segmented.
    – Law-enforcement collaboration: victims should upload ransom note (README_README.txt) and a non-sensitive sample to NoMoreRansom/EC3 Europol or CISA incident response—keys occasionally appear after takedown or indictments.

4. Other Critical Information

  • Unique Behavioral Signatures:
    – cl0p will purposely skip encryption of any file whose path contains windows, google, or program files to avoid bricking the OS; instead it hones in on large NAS/SAN volumes.
    – Some samples automatically exfiltrate a predefined list of file types (.pdf, .csv, .dwg, .pst) to cloud storage before encryption, enabling “double-extortion.” DLP and network-egress monitoring are therefore critical.
  • Broader Impact:
    – Over 1300 organizations—including universities, government agencies, and Fortune 500s—publicly confirmed hits.
    – Law-enforcement Operation Cyclone-bl (June 2021) arrested six affiliates; however, core developers continue to evolve toolchains (Rust rewrites observed 2024).
    – Contributed to global $91M USD ransom demand totals (Chainalysis 2024 report).