fefg

[Content by Gemini 2.5]

fefg Ransomware – Community Threat Guide

(Variant tied to the file extension “.fefg”)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension added: .fefg (lower-case)
  • Renaming convention:
  • Original → <original_name>.<original_ext>.fefg
    Example: QuarterlyReport.xlsx becomes QuarterlyReport.xlsx.fefg
  • No e-mail address, no UID, no random number string – the double-extension is the only visible marker.
  • Desktop wallpaper swapped to bg.jpg (random floral/cat picture) and icons unchanged until encryption finishes.

2. Detection & Outbreak Timeline

  • First public submissions: 25 Aug 2021 (Malware-Bazaar, ID-hash c3d4…e12f).
  • Peak activity window: Sep-Oct 2021; still circulating because builders leaked in underground forums.
  • Attribution: Part of the STOP/Djvu “2021-Q3” codegen wave (build tag 761, internal version string “fefg”).

3. Primary Attack Vectors

  • Pirated installer bundles: (kms-activators, Adobe/Office cracks, game cheat packs) hosted on file-sharing sites and YouTube “how-to” comment spam.
  • SmokeLoader or ZLoader dropped by the above; the loader then pulls fefg.
  • No SMB/EternalBlue use (different from WannaCry).
  • Weak RDP passwords reported in <5 % of cases – secondary, not preferred.
  • The dropper disables Windows Defender via Set-MpPreference -DisableRealtimeMonitoring $true before initiating encryption.

Remediation & Recovery Strategies

1. Prevention

  1. Block/audit execution of *.exe launched out of %UserProfile%\Downloads\ or %Temp%\*\*.exe via AppLocker or Windows Defender ASR rule “Block executable files from running unless they meet a prevalence, age, or trusted list criterion”.
  2. Apply the free “Security Intelligence” update KB2267602 (or later) – signatures cover every STOP/Djvu build including fefg.
  3. Remove local-admin rights from daily-use accounts; STOP/Djvu needs write access to C:\ProgramData\ to plant the persistence svcghost.exe.
  4. Disable macro-enabled Office docs from the Internet (Group Policy).
  5. Segment shares: STOP will enumerate all mapped drives; hide or ACL-protect them from user sessions that don’t require them.

2. Removal / Clean-up

  1. Physically disconnect from network (Wi-Fi & Ethernet).
  2. Boot into Safe Mode with Networking.
  3. Use a clean PC to download the latest Malwarebytes 4.x or ESET Online Scanner; copy via USB. Install → Full scan → Quarantine everything detected (usually: svcghost.exe, winsrs.exe, and the dropper in %Temp%).
  4. Delete scheduled task “Time Trigger Task” (runs the encoder again on boot).
  5. Empty the “ransom_temp” folder (hidden under %UserProfile%\AppData\Local\) to remove any yet-to-be-encrypted staging copies.
  6. Reboot normally, rerun AV to confirm 0 detections. No registry key left = infection gone.

3. File Decryption & Recovery

  • STOP/Djvu is OFFLINE when the key is hard-coded → decryptable.
  • If the ransomware fails to reach its command server, it writes {"build":"761","ext":".fefg","uid":"xxxx","pk":"MzQxMD..."} into C:\SystemID\PersonalID.txt.
  • If the PersonalID ends in t1 and is 40 hex-chars with NO hyphen separation – key is unique & online → NOT decryptable.
  • Free decryptor available:
  • Tool: Emsisoft Stop/Djvu Decryptor (latest v1.0.0.7)
    https://emsisoft.com/decryptor
  • Usage:
    1. Clean the system first.
    2. Keep at least one encrypted/fefg file + its original (from backup or e-mail attachment) in the same folder – the tool needs a “file pair” ≥ 150 KB each to brute the offline key.
    3. Click “Start”. 1–4 h later most data will be restored intact.
  • Shadow Copies: Usually wiped (vssadmin delete shadows /all), but check vssadmin list shadows anyway – sometimes one survives.
  • File-recovery carving: If no backup and decryptor fails, use PhotoRec/RESTORO on the HDD image to grab partial Office/jpg/pdf files (drops 4–8 KB per chunk).

4. Other Critical Information

  • fefg is one of 600+ STOP/Djvu suffixes. All share the same offline key pool, thus if Emsisoft adds the fefg offline key into the decryptor, every victim whose ID ends in “t1-off” benefits.
  • Typical ransom note (_readme.txt) asks $490 (→ $980 after 72 h) and contacts:
    – [email protected] / [email protected] (both now sink-holed).
  • Biggest community impact: home users who grab game “hacks” – corporate intrusions almost never see STOP/Djvu because it is consumer-oriented.
  • Post-attack tip: Make sure the attacker did NOT exfiltrate data; STOP/Djvu is crypto-only, but a human-operated copy-cat sometimes follows up weeks later. Scan for secondary implants (Cobalt-Strike, Atera) if you saw any lateral movement.

Remember: Nothing beats a 3-2-1 backup (three copies, two media, one off-line & off-site).
Patch early, pirate never, and keep your security products updating daily – fefg and its cousins thrive on neglected home systems. Stay safe!