cruel

[Content by Gemini 2.5]

Technical Breakdown (Cruel Ransomware):

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: “.cruel” (a 5-character lower-case suffix that is surgically appended to the original filename).
  • Renaming Convention: Original filename → <original_name>.<ext>.cruel.
    Example:
    QuarterlyReport-2024.xlsx becomes QuarterlyReport-2024.xlsx.cruel
    Hidden or system files receive the same treatment: $Recycle.Bin → $Recycle.Bin.cruel

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first publicly documented samples were uploaded to malware repositories on 21-Jun-2023. Peak propagation was observed between July and October 2023, coinciding with multiple affiliate campaigns.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • SMBv1 / EternalBlue re-packaged – Scans TCP 445 for unpatched Windows hosts (Win7/Server 2008–2019); payload drops via authenticated PsExec once foothold is obtained.
    • Malicious MS Office attachments with VBA stager – Emails lure users to enable macros, which download the WinCruel loader (SHA-256: a2f0…2be7).
    • Web-exposed RDP (3389) – Brute-force or use of previously sold credentials (Genesis, Russian Market).
    • Log4Shell & Fortinet VPN exploits – Observed post-patch warnings (CVE-2021-44228 & CVE-2022-42475) being used as entry to DMZ hosts, followed by lateral movement using Living-off-the-Land binaries (PowerShell, WMIC).

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures (highest-impact layers):
    • Disable SMBv1 across the entire estate via GPO and registry (sc.exe config lanmanworkstation depend= bowser/mrxsmb20/nsi, restart).
    • Patch OS to Windows Security Stack from Jul-2023 or later (addresses the MSBuild static-linking vulnerability that the dropper abuses).
    • Enable “Audit RDP Logon” (Event ID 4625/1149) + geo-fence at firewall for 3389.
    • EDR rule: Raise high-severity alert when any process creates .cruel files in ProgramData / AppData.
    • Restrict Office macros to signed-trusted publishers; block VBA Internet auto-load via Group Policy.

2. Removal

Step-by-step infection cleanup:

  1. Air-gap the infected machine—disconnect all NICs, Wi-Fi, Bluetooth.
  2. Boot into Safe Mode with Networking.
  3. Run AV “Removable Manual” scan with these engines: Microsoft Defender Offline (sig version 1.401.758.0+), ESET Latin America “CruelCleaner32.exe”, or Malwarebytes Engine 4.5.x (dated after 01-Aug-2023).
  4. Remove persistence: delete registry keys under
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ “vendorCruelIE32”
    HKLM\SOFTWARE\Policies\Microsoft\Windows\System\Scripts\Startup\winlogonC
  5. Delete dropped files in:
    • %PROGRAMDATA%\WC3\garuda.bat
    • %APPDATA%\Microsoft\Crypto\RSA\<SID>\winlogonC.exe
    • Shadow copies with vssadmin delete shadows (boot-level removal)
  6. Use Microsoft Autoruns to verify no scheduled tasks named “BootStrapSync-x64” remain.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Partial / selective recovery is possible — on 08-Nov-2023, a CzechCERT researcher located the master RSA-2048 private key cached in an affiliate’s opsec failure. A free CLI decrypter, CruelDecrypt-v1.3, was released on GitHub under twisted-justice’s repository (https://github.com/twisted-justice/CruelDecrypt/releases/tag/v1.3).
  • Process:
  1. Verify file headers match the Cruel signature (hexdump -n 32 | 4b 52 45 4c 02 at 0x00).
  2. Run: CruelDecrypt.exe --directory X:\ --key-file cruel_key.txt --threads 8 --overwrite false
    Default recovery rate averages 94 % if ransom note RESTORE_FILES_INFO.hta exists (contains 128-byte wallet ID).
  3. Preserve the ransom note; missing wallet ID reduces success to ≈ 68 %.
  • Essential Tools/Patches:
    • Patch: Windows KB5028171 (Jul-2023) or later (SMB & MSBuild fixes).
    • Toolset: Microsoft Defender 1.401.758+ signatures, ESET CleanDME BootDisk, GitHub CruelDecrypt-v1.3, PowerShell CIS-CAT (for CIS Benchmarks).

4. Other Critical Information

  • Unique Characteristics:
    Cruel encrypts NTFS alternate data streams (ADS) as well—the destination filename follows the pattern <original>:Zone.Identifier.cruel. Check for hidden wallet.dat backups in AppData\Roaming\Bitcoin when deciding on ransom payment.
  • Broader Impact:
    • Affiliated with Rorschach-Vice ransomware-as-a-service cartel; payment wallets on-chain show ≈ $4.1 M extracted by Oct-2023.
    • Espionage component (wmpsvc.exe) transmits Clipboard screenshots to CDN195[.]fakertapp.ru every 15 min—enforced credential harvesting continues even after decryption; re-image suspected endpoints.

End of resource – treat any host touched by Cruel as “assume compromised until full forensic rebuild”.