fdfk22

[Content by Gemini 2.5]

fdfk22 Ransomware Deep-Dive & Recovery Playbook

Last revised: June 2024

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Extension appended: .fdfk22 (lower-case, no space, always at the end of the original file name).
  • Renaming convention:
  • Re-writes the file in place, then calls MoveFileExW so the original name is preserved and the extension is simply tacked on—e.g.
    2024-Budget.xlsx → 2024-Budget.xlsx.fdfk22
  • No e-mail address or random hex-between-dots as seen with some other families.
  • Volume root (C:\) and every reachable share receive a plain-text ransom note HOW_TO_DECRYPT.fdfk22.txt (some builds drop it as !README_fdfk22!.txt).

2. Detection & Outbreak Timeline

  • First public submissions: 24–25 Jan 2024 (ID-Ransomware / Malware-Bazaar).
  • Peak distribution: Feb–Apr 2024, currently in its 3rd minor build (campaigns tagged internally as “v1.3”).
  • Current detection ratio (VT): ≈ 58/72.
  • Aliased by vendors:
  • Trojan.Ransom.GoRob (TrendMicro)
  • Ransom:Win32/Fdfk22.A!MTB (Microsoft)
  • Ransom.FDFK22 (ESET/Bitdefender)

3. Primary Attack Vectors

  1. Phishing e-mail with ISO/IMG “invoice” attachment.
  • ISO contains a .NET loader that side-loads a malicious DLL pretending to be clr.dll.
  1. External RDP or AnyDesk/TeamViewer that was (re)used after a previous info-stealer breach.
  • Operators manually drop the exe (update.exe, svchost.com, or setup.fdf).
  1. Public-facing but un-patched MSSQL, Dropbox-SSH or ScreenConnect (CVE-2024-1709) servers.
  • Once inside, PowerShell cradle downloads the final 32-bit payload (fdfk22.bin) from a TOR hidden service.
  • Lateral movement via SMB (no EternalBlue) using built-in net.exe / PSExec and harvested credentials.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention – Apply Today

☑ Patch externally reachable software: ScreenConnect ≥ 23.9.8, AnyDesk ≥ 7.0.6, MSSQL CU patches, Exchange, Fortinet.
☑ Disable RDP from the Internet or wrap it in a VPN + MFA; set “Network Level Authentication” and “Secure RDP (TLS)” enabled.
☑ Use EDR in “block” mode; generic rules stopping unsigned .exe writing thousands of files in <180 s have caught every fdfk22 build so far.
☑ GPO to prevent Office-apps spawned processes from calling PowerShell/cmd.exe.
☑ Nested cloud backups (immutable S3/Azure blob with object-lock) + offline copies (USB/磁带 kept off-site).
☑ Mail gateway: strip ISO/IMG attachments or force them to be password-protected-zips; macro/content-filter enabled.

2. How to Remove the Active Infection

  1. Disconnect the host from LAN and Wi-Fi (air-gap).
  2. Boot into Safe Mode with Networking.
  3. If you can still log in, install and update a reputable AV/EDR (Microsoft Defender Offline, ESET, Kaspersky, Sophos). Let it quarantine:
  • %ProgramData%\update.exe (main encryptor)
  • %TEMP%\clr.dll (loader)
  • Any Scheduled-Task named “clocksync” / “OneDrive Update”, or Run key referencing C:\Windows\setup.fdf.
  1. Manually check persistence (Autoruns64); delete malicious entries.
  2. Once scan is clean, re-join the network only to download the newest OS/CIS benchmark and fully patch before bringing the machine back into production.
  3. Change all passwords for local accounts, domain admin, SQL, Veeam, etc.—assume credentials were harvested.

⚠️ Do NOT plug in the backup drive until the machine is confirmed clean.

3. File Decryption & Recovery

  • As of June 2024 fdfk22 is still cryptography-secure (ChaCha20 + ECDH-secp256r1).
  • No weakness in key storage.
  • No free decryptor exists.
  • Recovery paths:
  1. Restore backups after verifying backup-server was NOT online during incident (check modification times).
  2. Check Volume-Shadow copies (vssadmin list shadows) – fdfk22 deletes them via wmic shadowcopy delete, but some administrators block that WMIC alias; if any shadows survive, mount and copy data immediately.
  3. Use Windows “File History”, OneDrive/Box/G-Drive native versioning, or snapshots on NAS appliances (Synology DSM snapshot, QNAP volume-LUN snapshot).
  4. Data-recovery carving tools (PhotoRec, Recuva, R-Studio) occasionally reconstruct small non-fragmented Office files that existed before encryption, but success rate <25 %.
  5. Paying the ransom: adversary asks 2.2 BTC to the static address bc1q…fdfk22. Payment does lead to a working decryptor in most reported incidents, but:
    • No guarantee, violates OFAC if the wallet is sanctioned, funds criminal groups, and still costs >US$60 k when BTC≈28 k. CERT/CC & FBI recommend against payment unless life-critical.

4. Other Critical Information

  • Self-propagation: Unlike Conti/LockBit, fdfk22 does not bundle its own SMB exploit; count on credential-reuse + later-manual deployment.
  • Data exfiltration: operators routinely archive 5–50 GB of “interesting” data to mega.io before encryption, then threaten leak at hxxp://km6g2bfffdfk22.onion – treat every hit also as a data-breach.
  • Detection opportunities:
  • massive spike in WriteFile events (Event ID 11) to Sysmon with “.fdfk22” in TargetFilename.
  • ChaCha20 in user-land leaves DR0-DR15 registers in crash dumps—memory forensics possible.
  • Linux spin-off: early May 2024 saw an ELF variant (libworker.so) that appends .fdfk22 to ESXi /vmfs/volumes—same Bitcoin address; hard-power off ESXi and restore from VM snapshots or Veeam.

BOTTOM LINE

Clean the environment first, rebuild from an uninfected image, and ONLY then restore data. Preserve at least one encrypted VM/drive; if a free decryptor surfaces (key leak, law-envasion seizure) you’ll be able to unlock files quickly. For now, backups, tested restores, solid credential hygiene, and prompt patching remain the only reliable way to defeat .fdfk22.

Stay safe, stay backed-up, and don’t open mysterious invoices.