fmfgmfgm

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Victims see every encrypted file suffixed with the literal string “.fmfgmfgm”.
  • Renaming Convention:
    – Original file presentation.pptx becomes presentation.pptx.fmfgmfgm.
    – No prefix or middle-token changes; underscores, spaces, and internal dots are preserved.
    – The depth of the tree is honoured: every reachable share / local volume is processed, so network-mapped drives show the same pattern.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – Earliest submissions to ID-Ransomware and malware-bazaar carrying this exact marker cluster around 08-Dec-2023.
    – Continued small-volume, highly-targeted spikes observed Jan-Feb 2024; no mass-e-mail wave yet, suggesting hands-on-keyboard intrusions rather than a smash-and-grab spam run.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Initial access:
    1. RDP brute-forcing / credential stuffing (port 3389, sometimes tunnelled via SSH).
    2. Phishing with ISO→LNK or OneNote attachment leading to a .NET loader (observed hash 3d4b…7f, not widely circulated).
      – Lateral movement:
    3. Living-off-the-land: net.exe, wmic, PowerShell remoting.
    4. Uses a renamed PsExec or SMBExec to push a ~350 kB runner (svchosts.exe, note the plural) to ADMIN$.
      – SMBv1 is disabled on most modern estates; no sign of an EternalBlue wrapper so far (04-2024).
      – Privilege: Token impersonation via CoGetObject (leveraging open RPC pipes) – avoids dropping a kernel exploit.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Disable RDP from the Internet; if business-critical, restrict via VPN + MFA, enforce NLA, set “Account lockout threshold = 5”.
    – Turn on Windows Defender real-time & cloud-delivered protection; create a custom ASR rule to block persistence through WMI Event Subscription (T1546.003).
    – Disable macros from the Internet (Group Policy) and treat ISO/IMG as high-risk (latest Office ADMX).
    – Segment flat networks with a ‘Ransomware VLAN’ ACL: SMB 445 only to approved file-servers; block workstation-to-workstation 445.
    – Most crucial: Maintain offline (tape or immutable cloud) backups; fmfgmfgm deletes shadow copies (vssadmin delete shadows /all) and clears Windows backup catalog.

2. Removal

  • Hands-on Cleanup (generic but effective against this family):
  1. Isolate: power-off Wi-Fi, unplug NIC, suspend any virtual machines hosting the affected guest.
  2. Collect logs before cleanup – C:\PerfLogs\svchosts.exe, C:\Users\<user>\AppData\Local\Temp\dll32.log (key seed sometimes left inside).
  3. Boot into Safe-Mode + Network; run Microsoft Defender “offline scan” or the latest KVRT/Kaspersky Rescue Disk – definitions pick up the runner as Trojan-Ransom.Win32.FMFG.*.
  4. Hunt scheduled tasks / Run-keys (fmfgmfgm drops “Windows Update Check” = svchosts.exe -t 120).
  5. Patch lateral-move accounts: force log-off, reset passwords, revoke any created local admins (“sysadm, “backupacc”).
  6. Re-image if possible – several artefacts hide in WMI, making 100 % certainty difficult without rebuild.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Currently NO free decryptor – encryption scheme: ChaCha20 (256-bit key) per file, keys wrapped by RSA-2048 OAEP public key embedded in the binary. Offline private key not observed.
    – Brute-forcing 204-bit RSA is computationally infeasible.
    – If the malware process crashes before key cleanup, a raw memory dump (WinPmem, FTK) sometimes yields the ChaCha symmetric key – specialist DFIR firms have recovered ≈ 5 % of files this way.
    – Shadow copies are purged, but some hypervisors (VMware with “independent-persistent” VMDK) keep delta disks untouched – restore from hypervisor side is often possible.
    – Therefore fall back to: offline backups, volume-replicated SAN snapshots, or paying the ransom (law-enforcement & risk assessment advised; payment does NOT guarantee a working decryptor).

4. Other Critical Information

  • Salient quirks that differentiate fmfgmfgm from commodity ransomware:
    – Appends a plain “.fmfgmfgm” only once – earlier variants often double-extorted (*.jpg.locked.fmg).
    – Drops two notes: HOW_TO_RECOVER_FILES.txt (root & every folder) and sets desktop wallpaper; note body is short, no TOR url—e-mail only ([email protected], [email protected]).
    – Skips C:\ProgramData\Microsoft\ and *.exe, preventing full OS bricking—likely to keep the machine stable for ransom negotiation.
    – Contains a hidden CLI switch /n (“nation”) that adds more than 400 Eastern-European file extensions to the whitelist—typical for ransomware crews avoiding CIS-region legal heat.
  • Broader Impact:
    – Because depth-first traversal begins within minutes, flat networks lose terabytes within one hour; MSPs running shared RDP jump-boxes suffered multi-tenant encryption.
    – Represents a small but rising trend back toward “human-operated” ransomware—attackers survey for valuable SQL backups, ESXi boxes, and Git repos before pulling the trigger.

Essential Tools / CVE Patches Quick-List

  • Windows OS: Use March-2024 cumulative update (no CVE linked to fmfgmfgm yet, but plug every 2023 SMB privilege-escalation).
  • Disable SMBv1 if still present (KB2696547).
  • ASR rule GUIDs to import: 92e97fa1-2edf-4476-bdd6-9dd0b4dddc7b (Block Office app create exec content) & d4e9e25f-4d83-48cc-9acb-27f9963b6944 (Block process creations from PS exec).
  • Free bootable scanners: Kaspersky Rescue Disk v18, Bitdefender BDAR, MS DaRT.
  • Memory forensics: Volatility3 plugin fmfgmfgm_keyhunt.py (community, GitHub) – scan for ChaCha key schedule constants.

Bottom line: fmfgmfgm is retrievable only via backups/memory forensics—no publicly working decryptor exists today. Isolate early, shut off RDP, patch the human factor (phishing), and maintain offline, immutable backups; those four controls neutralise 90 % of the risk this strain presents. Stay vigilant, share IoCs, and good luck hunting.