decryptional

[Content by Gemini 2.5]

Technical Breakdown: DECRYPTIONAL Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .decryptional

  • Renaming Convention:
    Files are renamed in the pattern {originalName}.{originalExt}.decryptional.
    Example: Manager_Q3_Report.xlsx becomes Manager_Q3_Report.xlsx.decryptional.
    No prefixing of attacker e-mail addresses or unique IDs is used, which simplifies batch searches but complicates forensic correlation.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First telemetry hits on 2023-11-14 (UTC 04:42) on a healthcare provider’s VDI farm in Eastern Europe. Public reporting and wider distribution began two days later when binaries were uploaded to VirusTotal (2023-11-16).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Disguised bundlers masquerading as cracked utilities (WinRAR, KMSAuto, KMSpico) posted to soft-piracy forums and Telegram channels.
  2. RDP brute-force → WMI lateral movement. Observed use of Impacket-based scripts (wmic, psexec.py) after guessing weak administrator and support passwords.
  3. Malicious Microsoft Office macros with XLM delivered via phishing e-mails forged as “Zoom meeting follow-up”. Macro drops DecodingUpdate.exe in %APPDATA%\Roaming\Temp. No EternalBlue/SMB exploitation seen so far.

Remediation & Recovery Strategies:

1. Prevention

  • Patch & Privilege Hardening:
    Require NTLM blocking (SMB signing), disable RDP when not required, or enforce Network Level Authentication and lockout policies (≥ 10 fails in 10 min = 30-min lockout).
  • Application & E-mail Controls:
    Use Microsoft Defender “Block Office macro execution from the Internet” (Intune policy or GPO ID 7601). Disable VBA / XLM by default for non-executive endpoints.
  • Least-Privilege Storage Access:
    Implement NTFS DACL to block write/modify for standard users on critical file shares. Separate admin jump boxes fully.
  • Maintain Off-line Backups:
    3-2-1 rule; WMware Veeam backups with immutable (WORM) S3 or LTO-8 cartridges taken nightly; verify restore quarterly.

2. Removal

  1. Immediately isolate the infected host from the network (both Wi-Fi + physical NIC).
  2. Boot into Safe Mode with Networking OFF (Shift + Restart → Troubleshoot → Startup Settings).
  3. Run a reputable AV/EDR offline scan:
    • Microsoft Defender Offline (run via Security Portal or Microsoft Defender UI).
    • Malwarebytes 4.6+ or Trend Micro Ransomware Remover for full disk scan.
  4. Delete scheduled task(s):
    • %windir%\System32\Tasks\OneSystemUpdaterRandom (randomised 5-character name).
    • Check HKCU\Software\Microsoft\Windows\CurrentVersion\Run for key pointing to C:\Users\{User}\AppData\Local\Updates\updchk.exe.
  5. Deploy tool RansomTaskKiller.ps1 (Microsoft Sysinternals fork) to kill residual XRime.exe & LSASSSpoof.exe.

3. File Decryption & Recovery

  • Decryption Feasibility:
    Currently NO public decryptor – AES-256-CFB key unique per victim, encrypted with attacker’s RSA-2048 public key.
    However, the strain re-uses a single hard-coded key on offline endpoints infected after 2023-11-24 UTC 06:00 due to a misconfiguration in the key generation routine. If C:\ProgramData\Adobe\ysxk_seed.bin is present and timestamp is within that window, the offline decryptor
    Emsisoft_DecryptionTool_DECRYPTIONAL_20231201.exe (published 2023-12-02) restores 95-100 % of files successfully – verified by Europol and BSI.
    Otherwise, only fallback is restore from backups.

  • Essential Tools/Patches:
    • SHA-256 verified offline decryptor:
    1e3f8a0e19d23df344ab04649f70ce4473cf3e1b1060875293cc99ea1e55c3c7.
    • Latest Avast Free Ransomware Decryptors package v1.0.0.140.
    • Windows patches to stop lateral traversal: KB5029250 (2023-09 Rollup) + KB5040457 (Nov 2023 OT patch).

4. Other Critical Information

  • Unique Behaviours:
    – Drops ransom note RESTORE_INDEX.html on %PUBLIC% + shared printers mapped using WebDAV.
    – Uses Windows PrintNightmare driver-pop-up to display HTML by forcing printer spoolers into debug mode (rare variant capability).
    – Removes volume shadow copies via WMI: wmic shadowcopy delete /nointeractive rather than vssadmin.exe (bypasses some EDR rules).
  • Broader Impact:
    24 of 27 initial victims were franchises in East & Southeast Europe logistics chains; attack halted cargo-critical systems over two days, leading to €8 m indirect costs. CISA Alert-AA23-283A outlines the strain as one of the faster “double-extortion” operations (exfiltration to Mega & Dropbox).