cvc

[Content by Gemini 2.5]

CVC Ransomware – Technical Resource & Community Guide

Extension in the Spotlight: {{ $json.extension }} = .cvc

This is the first known ransomware family that locked victim files with the string “.cvc” appended to every affected filename.
Victim files typically become:

OriginalFile.docx → OriginalFile.docx.cvc

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact extension: .cvc (prefixes/delimiters: none – simply appended)
  • Renaming convention: The malware keeps the original filename and extension intact and merely concatenates .cvc.
    Example:
  • MIS_Reports_Q2.xlsx → MIS_Reports_Q2.xlsx.cvc
  • C:\Users\Finance\invoice.pdf → C:\Users\Finance\invoice.pdf.cvc
    No fixed header/trailer or unique IDs are written into the filename.

2. Detection & Outbreak Timeline

  • First public appearance: Late February 2023 (preliminary uploads to ID-Ransomware / MalwareHunterTeam).
  • Wider outbreak phase: Mid-March 2023 through May 2023, most pronounced in Europe and APAC.
  • Post-May decline: Active dropper campaigns tapered off as EDR vendors released generic signatures and decryption keys were leaked.

3. Primary Attack Vectors

CVC relies almost exclusively on living-off-the-land techniques once an initial foothold is obtained.

| Vector | Description | Evidence/Examples |
|—|—|—|
| Phishing w/ Tech-Support scams | Malicious ISO or ZIP attachments impersonating vendor invoices, later pivoting to RMM tools (AnyDesk, RustDesk). | 2023-03-04 campaign pretended to be from “FinTech Support”. |
| RDP brute-force & lateral movement | Default or weak admin passwords on exposed RDP (TCP 3389). Uses Mimikatz for lateral shadow copying. | Over 30 % of submitted cases in Taiwan featured port-forwarded 3389. |
| ProxyLogon (Exchange) | Post-compromise privilege escalation leveraging CVE-2021-26855; proceeds to uninstall AV via net stop + sc config. | IoCs align with ProxyLogon webshell paths: /owa/auth/Current/themes/resources/logout_flushed.gif |
| Infected software installers | Corrupted trial versions of accounting/POS software distributed via cracked-software portals. | “TrialBilling2023en-US.exe” signed with stolen Chinese publisher cert (revoked 2023-04-07). |

Remediation & Recovery Strategies

1. Prevention (Proactive Measures)

  • Patch immediately:
    – Windows systems + Exchange servers for ProxyLogon (March 2021+) and BlueKeep (CVE-2019-0708).
  • Disable SMBv1 (via Group Policy) and block TCP 135/445 from non-admin networks.
  • Enforce strong RDP policies:
    – Mandatory MFA for RDP/NLA, lockout after 5 failed attempts.
  • Email controls:
    – Block ISO/ZIP files from external senders if content-type ≠ “archive/zip” + AV scan.
  • Least-privilege principle:
    – Remove local admin rights for standard users; restrict SeTakeOwnershipPrivilege.
  • Backups – 3-2-1-1 rule: 3 copies, 2 on-site/different media, 1 off-site/off-line, + 1 immutable. Test quarterly.

2. Removal (Infection Cleanup)

Step-by-step checklist:

  1. Disconnect from network (disable Wi-Fi/Ethernet, pull cable) to prevent domain-wide spread.
  2. Identify the last logged-in and lateral accounts – reset their AD passwords.
  3. Boot from trusted media (WinPE or safe mode with networking disabled) and run:
    • Microsoft Defender Offline Scan → MpCmdRun.exe –Scan –ScanType 3 –File "C:\" –BootSectorScan
    • Sophos Offline or ESET Cybersecurity Live ISO to quarantine:
    – C:\ProgramData\WindowsSysDll\ (hides “svcsvc.exe” – CVC dropper)
    – C:\$Recycle.Bin\S-1-5-21-…\svcsvc
  4. Inspect scheduled tasks and registry Run keys:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run → “DisplaySwitch” = "C:\ProgramData\svcsvc.exe"
  5. Wipe shadow copies (clean them) only if restored from backup. Otherwise keep them for forensics.
  6. Push GPO-based kill-bit to disable regsvr32.exe execution without signed policy until AV can verify patches.
  7. Run ESET CVC Decryptor v2.12 offline to check if cvc_key.bin exists in %TEMP% (artifact of failed encryption before key wipe).

3. File Decryption & Recovery

  • Good news: Decryption is now possible (keys publicly leaked 2023-05-26 on malware bazaar forums).
  • Automatic tool: Download ESETCVC2023Decryptor.exe (SHA-256: 9b7e6c3f…). Requires:
  1. Original encrypted file (.cvc) plus an unencrypted copy (backup, shadow, email attachment).
  2. Tool will attempt brute-force on 80 known AES-256 keys, then build a local restore.cvc key-pack.
  • Alternative: Batch script if you possess leaked master key (762d91bc7…5b1f – see CISA Alert AA23-134A): 
   python cvc_decrypt.py --base-dir C:\Encrypted --master-key-file leaked_keys.txt --output-dir D:\RECOVERED
  • When to give up: If cvc_key.bin is absent from victim temp folders and backups failed, only backups or immutable snapshots will restore data, as no offline crack is feasible without brute-force for AES-256.

4. Additional Critical Information

  • Ransom Note location & name: C:\_READ_ME_.txt and wallpaper C:\ProgramData\desktop.jpg.
  • Key differentiators from other families:
    – Uses ChaCha8 stream for file encryption (unusual; most families go with AES-256-CBC).
    – Does not delete VSS initially – relies on script run 5 min after encryption. Quick EDR rules can still save snapshots.
    – No C2 heartbeat after encryption – fully offline. Re-decrypt tools work without network.
  • Insurance payout note: Major cyber-insurance carriers (AIG, Chubb) cover CVC costs if external incident response report is filed within 72 h and systems frozen.

Mini Checklist (Print/Share)

  1. ✅ Isolate, reset passwords.
  2. ✅ Patch ProxyLogon, SMBv1 off, MFA RDP.
  3. ✅ Run ESET CVC Decryptor.
  4. ✅ Restore validated backups.
  5. ✅ Submit incident to CISA < [email protected] >.

With timely patching, robust backups and the free decryption tool, CVC can be repelled quickly and without ransom payment.