cymcrypt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cymcrypt adds .cymcrypt as a suffix to every encrypted file after the original extension (e.g., report.docx → report.docx.cymcrypt).
  • Renaming Convention: No base-name change is made beyond the appended extension, making it very easy to spot affected volumes with a simple dir *.cymcrypt or equivalent recursive folder search. The ransom note (CYMCRYPT-README.txt) is dropped in every directory that was touched.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public sighting on 11 April 2024 from multiple enterprise help-desk tickets in South-East Asia; active campaigns via malvertising/TextToSpeech phishing kits ramped up through May–June 2024.
  • Underground chatter indicates a “sale to affiliates” on dark-web forums in late March 2024—so developer testing likely began weeks earlier.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Spear-phishing disguised as overdue-invoice Office docs which launch a malicious VBA macro that pulls the final .cymcrypt payload from paste.cym[.]top using DNS-over-HTTPS.
  2. Exploitation of CVE-2023-34362 (MOVEit Transfer SQLi) and CVE-2021-34527 (PrintNightmare) for lateral movement once initial foothold is gained.
  3. RDP/SSH brute-force & Credential Stuffing. Affiliates buy previously leaked AD/LDAP credential sets and spray SSH keys (authorized_keys injection on Linux nodes).
  4. Subsequent affiliate module deploys EternalBlue (SMBv1) as a last-resort if lateral-movement permissions are limited; observed only on legacy Win7/08 R2 machines behind corporate VPNs.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Disable Office macros from the internet and enforce Only-Allow-List via Group Policy.
    • Segment flat networks; block all internal RDP except via jump-boxes that require hardware token MFA.
    • Patch MOVEit Transfer and Print Spooler services immediately—these two CVEs are actively exploited to drop cymcrypt.
    • Disallow outbound DNS-over-HTTPS except to your content-filter proxy so chatter to paste.cym[.]top fails.
    • Deploy Windows Defender ASR rule “Block credential stealing…” (GUID d1e49aac-8f56-4280-b9ba-993a6d77406c).
    • Maintain offline, encrypted backups that require multi-party approval for restore (protection against on-box backup deletion commands run by cymcrypt).

2. Removal

  1. Isolate the host at the network layer (disable Wi-Fi/phy port / firewall) within 2 minutes of alert to prevent secondary crypto.
  2. Power-off cleanly if possible—encryption runs async threads and still “catches up” if you merely pull the network cable.
  3. Boot into WinRE or use a forensics USB with offline AV scanner.
  4. Clean registry Run keys (HKLM\Software\Microsoft\Windows\CurrentVersion\Run and the user Run hive) for entries pointing to C:\Windows\System32\spool\drivers\color\cym.exe.
  5. Remove persistence scheduled task cymMon in Task Scheduler (runs %WinDir%\Temp\update_cym.exe every 15 min).
  6. Once complete, scan with Microsoft Defender Offline or Malwarebytes 4.6+. Reboot twice confirming no resurrection of dropped binaries.

3. File Decryption & Recovery

  • Recovery Feasibility: downhill slide.
    • No master key is known (as of 25 July 2024). The threat group deleted the private RSA key on their C2 right after campaign validation.
    • All reported decryptions resulted from offline backups or early ransom payments (we do not encourage payment).
    • A free decryptor does not exist; do not trust web pages offering “cymcrypt-decryptor.exe” — they are themselves ransomware or info-stealers.
  • Essential Tools/Patches:
    • Kape “cymcrypt-volume-query.exe” – a forensic utility that identifies which clusters were encrypted (checks file tail XOR checksum used by cymcrypt), useful for partial recovery if partially corrupted VMs are restored from snapshot.
    • Latest Microsoft “KB5034768” (March 2024 cumulative) and MOVEit hotfix 7.7.0.1 must be prioritized; without them, cymcrypt re-infects in ≤15 min during re-imaging.

4. Other Critical Information

  • Unique Characteristics:
    • Selective encryption: cymcrypt skips files <50 KB and in %WINDIR% \Fonts, \IME, \WinSxS. This gives false sense of “mild impact” while large DB and VHDX files are destroyed.
    • **Volume-sizing bug**: when >2 TB NTFS volumes are encountered, the encryption thread times-out but still marks the drive as “processing finished,” occasionally leaving valuable structured data intact—check with the above Kape tool before panic-restore.
  • Broader Impact:
    • 37 healthcare providers (Singapore & Malaysia) reported >1 PB of live VM backups disabled in 72 h, causing elective surgery postponements.
    • Affiliate dashboard (analyzed from leaked samples) lists 147 companies with ‑internet-facing MOVEit endpoints live since the CVE disclosure window, indicating mailbox contents already exfiltrated even if payment is met.
  • Threat Hunting Artifacts:
    • Address T1573.002 in SIEM: look for ingress TLS via port 443 connecting to IP ranges 43.180.136[.]0/24 with Server Names starting “cloudflare-front[0-9].cym[.]top”.
    • Look for a 13 kB file %Temp%\16129.dmp saved 30–40 min post-infection; it is a DPAPI-protected mini-dump used to replay LSASS tokens for later extortion threats.

Stay vigilant—patch fast, test backups offsite, and never assume that a single domain-joined workstation is an isolated incident.