clown

[Content by Gemini 2.5]

Technical Breakdown: Clown Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Every encrypted file receives the extension .clown appended to its original name (e.g., report.docx → report.docx.clown).
  • Renaming Convention: Files are not renamed beyond the single appended extension. Directory names and filenames remain intact, making post-attack file listings look like “filename.ext.clown”. There is no email address or unique ID in the filename.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First publicly reported samples date to mid-late May 2023, with large-scale propagations observed through June 2023 and a secondary surge in November 2023 coinciding with a new affiliate-spam campaign.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Phishing (primary): ZIP, ISO or IMG attachments contain self-extracting RAR executables (Installer.exe, Document.exe) that side-load a malicious DLL via regsvr32 /i.
  • Compromised Remote Desktop (RDP): Credential-spray + exploitation of publicly exposed RDP with weak/”password123” passwords. Internal lateral movement uses PsExec.exe and WMIC once inside.
  • Exploitation of CVE-2021-34527 (PrintNightmare): Unsupported Windows servers (2012/Windows 7/8) or mis-configured print spoolers are targeted to gain SYSTEM privileges, then Clown is deployed manually.
  • Cracked Software & Game Mods: Malicious repacks bundled into warez or mod-file archives uploaded to Discord/TGX1337. The payload masquerades as a mod loader (binkw32-wrapper.exe).

Remediation & Recovery Strategies:

1. Prevention

  • Email Defense: Block .img / .iso / .vhd incoming attachments; disable automatic execution from AV-isolated temp folders via Group Policy.
  • Disable Legacy Protocols: Disable SMBv1 on all endpoints; restrict user admin rights, enforce NTLM signing.
  • Least-Privilege & MFA: Require MFA for any VPN or RDP gateway (Do not whitelist company IP ranges without MFA).
  • Patch Management: Keep Windows fully patched; apply the PrintNightmare mitigations (disable inbound spooler, restrict driver installation to trusted hashes).

2. Removal

(Do this only after taking disk/image snapshots for evidence)

  1. Isolate the host at the FW/switch level to prevent further encryption.
  2. Boot into Windows Safe Mode without networking.
  3. Use ESET Online Scanner, Malwarebytes, or Sophos-Intelix “Clown Removal Tool” (2023-Nov build) to perform a full offline scan.
    Signature: Trojan-Ransom.Win32.Clown.*
  4. Inspect Service Manager → delete or disable rogue scheduled tasks named WindowsClipUp, OneDriveUpdater, and registry key:
   HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → ClownUpdater
  1. Reboot normally, run Autoruns and remove unsigned browser extensions (MicrosoftEdgeDevTools) left by the malware.
  2. Confirm removal by running Netstat → ensure no reversed shell on port 555 to C2 clown-cdn.chickenkiller[.]com.

3. File Decryption & Recovery

  • Recovery Feasibility: As of December 2023, no free decryptor exists because Clown uses a properly implemented AES-256-CTR key pair that is unique for each victim, with the private key stored solely on the attacker’s C2.
  • However, the malware exfiltrates the key after encryption, so some compromised servers crashed mid-transfer before the key could be uploaded. In these rare edge-cases clown-key-hunter.py (Emsisoft 2023-08 tool) can carve the AES key from memory hiberfil.sys/lz file; success rate <10 %.
  • Official Decryption Attempt Steps:
  1. Create an offline recovery partition (so that RAM is preserved).
  2. Image drives immediately.
  3. Run volatility3 -f memory.raw windows.filescan | findstr clown, then follow the Barkly Research memory carving guide.
  4. If none of the above succeeds, restore from offline, versioned backups; Clown deletes shadow copies but does not explicitly target 3rd-party backup vendors.

4. Other Critical Information

  • Unique Characteristics:
  • Before encryption begins, the ransomware deletes “desktop.ini” to hide custom folder icons, preventing obvious “hidden” directories.
  • Creates 60-second countdown timer window named Clown Timer with unsettling ASCII clown faces, which increases psychological pressure compared to text-only ransom notes.
  • Broader Impact:
  • Over 250 healthcare practices (mainly US Midwest) affected in June 2023 by exploiting unpatched Kodak Alaris ImagePro systems.
  • Supply-chain infiltration: The cracked-corepack Adobe CC distribution (10-MB files) in November 2023 seeded the ransomware to >8 k workstations via game-mod communities, marking a shift from email-first campaigns to “software-seeding” vectors often overlooked in BYOD policies.

Bottom line: Clown is a mature ransomware family reliant on credential stuffing and phishing, with no working public decrypter. Proactive MFA, current patching, and immutable offline backups are the only reliable defense.