efvc

[Content by Gemini 2.5]

efvc Ransomware – Technical Intelligence & Clean-Up Guide

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .efvc
  • Renaming Convention:
  • Encrypts and APPENDS “.efvc” to every affected file.
  • Keeps the original file- and directory names so that:
    • Before: Spreadsheet.xlsx
    • After: Spreadsheet.xlsx.efvc
  • Creates a per-folder copy of the ransom note titled _readme.txt.

2. Detection & Outbreak Timeline

  • First publicly reported: Beginning of October 2023 (ID-Ransomware upload spike 2-Oct-23).
  • Attributable to the STOP/Djvu cluster, which usually sees weekly build/date-stamped variants (“efvc” = build string used during that week).
  • Still highly active through Q1-2024; most e-mail submissions arrive within 24–48 h of infection.

3. Primary Attack Vectors

  • Malspam attachments (password-protected ZIP or ISO containing the loader “.exe”).
  • Software-cracks / fake game cheats (KMSóto, cheat-engine, cracked Adobe, etc.) distributed via Bit-torrent/YouTube links.
  • Follow-up malware drops through existing infections (Vidar, RedLine stealer) that purchase pre-compromised machines.
  • No signs of self-propagation via SMBv1/EternalBlue or RDP brute. Distribution relies on user execution.

Remediation & Recovery Strategies

1. Prevention

  • Block exec-files inside archives/ISO at the mail-gateway.
  • Apply Windows patch cadence but especially disable Office macros and set the built-in AV to “Block Office from creating child processes”.
  • Use strong, unique local-account passwords; while RDP is not the prime vector, STOP sometimes lands through stolen creds.
  • Application whitelisting or at least Windows AppLocker to stop %LOCALAPPDATA%\Temp\*.exe execution that the Djvu installer favours.
  • Always offline backups (3-2-1 rule) and monitor for early encryption signals (sudden spike of .efvc file creations).

2. Removal

  1. Disconnect the box from LAN/Internet, but leave powered on (RAM evidence).
  2. Boot into Safe Mode with Networking (for driver downloads).
  3. Run a reputable AV/EDR full scan (Defender, Malwarebytes, Sophos, etc.). Today every major engine tags the STOP-efvc sample generically (Trojan:Win32/STOP).
  4. Delete scheduled tasks “Time Trigger Task” or “SystemSupports” created in %windir%\System32\Tasks\.
  5. Remove the dropped installer and the Windows-update-launcher copy normally living in:
  • %USER%\Downloads\ (original)
  • %LOCALAPPDATA%\<random>\ (copy executed from)
  1. Check HKCU\Software\Microsoft\Windows\CurrentVersion\Run for SysHelper entry and delete.
  2. Patch known software whose licence you tried to crack (to close “back-to-square-one” holes).
  3. Reboot – system is now crypto-free; your data still ends in .efvc.

3. File Decryption & Recovery

STOP/Djvu uploads the per-victim ECDH public-key to its server; files encrypted AFTER the key exchange become undecryptable offline.

  • If the malware failed to reach its key server it reverts to hard-coded offline-key-sets (“offline ID”).
    → Try Emsisoft STOP-Djvu Decryptor v1.0.0.6+

  • Download from https://emsisoft.com/ransomware-stop (or BleepingComputer mirror).

  • Click “Start Scan”; the tool figures out whether your .efvc pair is offline or online.

  • Offline IDs can be 100% reversed once the private key is donated; the tool keeps an internal list updated weekly.

  • Online-ID (ending in “t1”) files return “no key at the moment”—no commercial decryptor exists.

  • Data-recovery alternative: shadow copies usually wiped (vssadmin delete shadows), but still worth a vssadmin list shadows as some bundles forget the step.

  • Volume-repair software (PhotoRec, R-Studio) can only resurrect originals that were stored on an SSD whose TRIM block had not yet reclaimed space—low success.

Bottom line:
– 10-30% of users = offline key → decryptable.
– 70-90% = online key → only backups or ransom (not recommended).

4. Other Critical Information

  • Differential survival: the malware purposely spares “.exe/.dll/sys” inside \Windows\ so the OS keeps booting, but removes C:\Windows\System32\svchost.exe from its Windows Defender exclusion list and afterwards clears the exclusion list entirely (to keep Defender inert).
  • In some variants a second-stage clipper/Trojan (Vidar) exfiltrates credentials BEFORE encryption—assume every password on that PC is burned and reset.
  • Payment demand printed in _readme.txt: $999 / 50% discount if you e-mail them within 72 h at [email protected] / [email protected]. Compliance does not guarantee a working key, law-enforcement strongly discourages payment.
  • Extensive geographic spread—Russia, Brazil, India, Indonesia, USA all show high upload counts; no particular industry immunity.

Quick-Win Checklist for Sysadmins

☑ Enable controlled-folder-access (Win 10/11 built-in) for at least Documents, Desktop, etc.
☑ Roll out FSRM or NetApp FPolicy to block write of “*_readme.txt” which appears seconds before the encryption wave—gives you an automatic quarantine gate.
☑ Store one set of backups on object-storage with S3 versioning or immutable Azure blob; efvc can’t rewrite there even if domain-admin gets popped.

Stay alert, keep patching, and never run cracks. Good luck!