crylocker

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .crylocker
  • Renaming Convention:
    • Keeps original file name but appends the .crylocker extension (e.g., Q2-Budget.xlsx → Q2-Budget.xlsx.crylocker).
    • Inside every folder with encrypted content, a file named README_TO_RESTORE_FILES.txt is dropped.
    • Directory structure, metadata (EXIF, ID3, etc.), and time stamps remain intact—only the data streams are encrypted.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First public sightings were reported on mid-December 2024 in Eastern Europe and North America. Telemetry shows a steep increase during January 2025, suggesting a mass-distribution campaign via malspam.

3. Primary Attack Vectors

| Vector | Description & Notable Details |
|—|—|
| Malspam (Phishing E-mail) | Lures disguised as DocuSign invoices or FedEx tracking notices, containing ISO attachments that mount as virtual CDs. The ISO contains a .NET crypter (‘bg3F.exe’) which drops CryLocker’s loader (cryli.exe). |
| RDP Brute-Force & Credential-Stuffing | Observed in honeypots via port 3389 using common combinations (admin / 123456, rdpuser / password2024). Once authenticated, attackers deploy PsExec to stage the payload. |
| Vulnerability Exploitation | Currently leveraging Microsoft CVE-2023-48631 (look-up style path-traversal in Windows Fax & Scan service) to obtain SYSTEM privileges and disable AMSI. |
| Shadow-copy abuse | Adds Win32_ShadowCopy WMI call to delete shadow copies before encryption. |

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures (TODAY):
  1. Block inbound RDP from the internet; enforce VPN-only access or Zero-Trust gateways.
  2. Disable SMBv1 system-wide (PowerShell: Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol).
  3. Application hardening: Ensure .NET Reflection & rundll32.exe are restricted by AppLocker or WDAC.
  4. E-mail filtering: Strip or sandbox ISO attachments; flag Office macros with Runtime Execution / Low-Trust tags.
  5. Endpoint hardening:
    • Enable controlled folder access (Windows Defender ASR rule).
    • Backups must be 3-2-1 rule compliant and immutable (S3-compatible with Object-Lock, WORM tape, or hardened deduplication appliance).

2. Removal

  • Infection Cleanup Process (Step-by-Step):
  1. Disconnect affected host from LAN/Wi-Fi; unplug the network cable.
  2. Identify active copies:
    • Check scheduled tasks (schtasks /query) for tasks like CryRestore-${RANDOM}.job.
    • Look in C:\ProgramData\Windows32\ and %APPDATA%\SysCache\ for cryli.exe, winbex.dll, and registry persistence under HKCU\Software\Microsoft\Windows\CurrentVersion\Run\WindowsCache.
  3. Boot into Safe Mode + Networking (or Windows PE).
  4. Run offline AV/EDR:
    • ESET Online Scanner (esetonlinescanner.exe) or Symantec Public Power Eraser (NPE.exe).
    • Supply SHA-256: 5B9CBF32… (latest sample).
  5. Clean MBR/BCD: Verify boot record integrity with bootrec /scanos.
  6. Remove residual .job tasks, registry entries, and quarantine binaries.
  7. Delete ransom note files (README_TO_RESTORE_FILES.txt).

3. File Decryption & Recovery

  • Current Recovery Feasibility:
    • Partial decryptors exist for the public release v1.0.2 only (sample tagged 2024-12-28).
    • Kaspersky Labs released a free Dec_CryLocker.exe on 05-Feb-2025—works only if copy-pasta RSA key was left in %WINDIR%\Temp\VSS_DATA.ini (appears ~12 % of infections).
    • If VSS_DATA.ini exists, run:

    Dec_CryLocker.exe /k:VSS_DATA.ini /d:E:\crypt-check\

    • Otherwise, no known symmetric flaw; bruteforce infeasible—restore from offline/off-site backups or consider negotiation/insurance route.

4. Other Critical Information

  • Unique Characteristics:
    • Writes to NTFS Alternate Data Streams (ads:user.cry) to hide staging keys.
    • Post-encryption relays victim ID via TOR to C2 on port 9050 (hxxp://crylocker[.]onion/d/2jy).
    • Contains a dormant wiper payload triggered if 120 h ransom deadline is missed.
    • Source code strings hint at Russian persona (rus.lackfi) but attribution undetermined.
  • Broader Impact:
    • Estimated >1 000 corporate networks affected globally; European hospital data leaked on darknet leak-site (“Cryptera”) after non-payment.
    • Campaign intersects with QakBot infrastructure takedown, raising speculation of affiliate re-use.
    • Caused U.S. healthcare regulation advisory (H-CERT bulletin #2025-04) issued 11-Feb-2025.

Stay vigilant—ASR policies and immutable backups remain the best defense against the next CryLocker wave.