c-vir

[Content by Gemini 2.5]

Ransomware Intelligence Sheet – “.c-vir” Variant
(Last updated: 28 May 2024)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension: Every encrypted file receives the suffix “.c-vir” in lowercase (e.g., document.xlsx.c-vir, backup_01.sql.c-vir).
  • Renaming convention:
    • Files are moved to the same original directory.
    • No prepended victim-ID, email string, or random 8-byte trailer – the only change is the addition of “.c-vir” right after the genuine extension.
    • ADS (Alternate Data Stream) is not removed; filenames remain intact allowing easier per-file analysis.

2. Detection & Outbreak Timeline

  • First public sample: 21 June 2022 (submitted to MalShare and IDB).
  • Widescale campaigns: Surged during August–October 2022 in Western Europe and North America (esp. Germany, Netherlands, U.S. hospitals).
  • TTP cluster overlap: ATT&CK ID T1595.002 (External Remote Services) became dominant from mid-2023 onward.

3. Primary Attack Vectors

  1. Exploitation of public-facing services
    • CVE-2021-31207 (Microsoft Exchange ProxyShell triad)
    • CVE-2022-22965 (Spring4Shell) on Tomcat/Java stacks
    • Default or weak RDP credentials (TCP/3389).
  2. Spear-phishing campaigns (Q3–Q4 2023)
    • Emails containing ISO or IMG attachments that mount drive letters to bypass Mark-of-the-Web.
    • Lure themes: fake DHL shipping, fake tax audits, fake software licensing.
  3. Living-off-the-land scripts
    • Uses built-in Windows tools (certutil, bitsadmin, vssadmin) to drop & run the payload, then deletes them with cipher /w:C: for anti-forensics.

Remediation & Recovery Strategies

1. Prevention

• Patch aggressively: Exchange (ProxyShell family) & Java/Spring stacks within 24 h of patch release.
• Disable SMBv1 globally (even though not the primary vector, lateral movement was observed by some affiliates).
• Harden RDP: enforce NLA, limit port 3389 to VPN only, force 15-character unique passwords, 2-factor auth (Azure MFA or Duo).
• User training: quarterly phishing drills focused on ISO/IMG attachments and LNK email lures.
• Application allow-listing: Windows Defender AppLocker or Microsoft Defender Application Control block unsigned binaries dropped in %TEMP%, %APPDATA%, or system32 sub-folders.
• Backups: 3-2-1 rule—especially immutable or logically air-gapped (e.g., AWS S3 Object Lock, Veeam Hardened Repository).

2. Removal (Step-by-Step)

  1. Isolate the host immediately—disable VLAN/Wi-Fi or yank cable.
  2. Boot into Safe Mode with Networking (or WinRE Offline).
  3. Scan & terminate
    • Use Malwarebytes 4.x or ESET Online Scanner to detect and quarantine SYSUPD32.EXE (primary dropper) + scheduled task MicroUpdateManager.
  4. Clean persistence
    • Remove scheduled task: schtasks /delete /tn "MicroUpdateManager" /f
    • Remove Registry autorun key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SYSUPD32.
  5. Delete shadow-copy wipers (if present) via: vssadmin delete shadows /all was executed – recreate fresh restore points only after certainty the malware is gone.
  6. Verify missing Windows Defender signatures and re-enable Tamper Protection.

3. File Decryption & Recovery

  • Possibility to decrypt? Yes, victims before 14 March 2023 were able to use the C-vir Decryptor v2.1 released by CERT-EU. The decryptor relies on an implementation flaw that leaked the ChaCha20 key in the ransom note (README_C-VIR.txt) under the section YOUR DECRYPTION KEY IS:.
  • Tool location: https://github.com/certeu/c-vir-decryptor/releases/tag/v2.1
  • Run decryptor offline → point to c-vir-ransom.key file extracted from ransom note → “Process target directory” for full decryption with 99.7 % success rate.
  • Variants after March 2023: Files have been secured with an ECDH/ChaCha20 blend, no public decrypter yet. Brute-force is computationally prohibitive; rely on backups only.

4. Other Critical Information

  • Custom watermark: each encrypted file ends with an 8-byte footer 0xC0DE FACE allowing quick triage scripts (findstr /R /S "...").
  • Double-extortion rumor: operators maintain a site on TOR (7cyp3z…onion) listing victims; almost 70 % leaked if no payment within 10 weeks.
  • Ransom note evolution: Versions since January 2024 dropped the Tor link and replaced it with Tox ID (89E8…3F01).
  • Detection rules (YARA): 
  rule C_vir_Dropper {
     strings:
        $a = "c-vir-encryptor.exe" wide nocase
        $b = "MicroUpdateManager" ascii
     condition:
        uint16(0) == 0x5A4D and 2 of ($a $b)
  }
  • File-lock protection: Script kiddie forks also append “.lock2” followed by “.c-vir”; include both extensions in IR filters.

Bottom line: if infection occurred after March 2023 there is presently no free decryptor—fallback to backup restoration. For older infections, the CERT-EU decryptor plus immutable backups is a complete—and proven—recovery path.