filock

[Content by Gemini 2.5]

Technical Breakdown

(Ransomware that appends the extension “.filock”)

1. File Extension & Renaming Patterns

  • Confirmation of file extension: .filock
  • Renaming convention:
  • Original: Quarterly_report.xlsx
  • After encryption: Quarterly_report.xlsx.filock
  • Filename, path, and directory structure remain intact—only the extra suffix is added.
  • Because the base name is preserved, victims can still see what was lost, which helps when rebuilding from clean backups.

2. Detection & Outbreak Timeline

  • First public submissions: mid-August 2022 (earliest VirusTotal hashes tagged “.filock”).
  • Wider distribution spike: October-December 2022, when multiple MSSPs recorded co-occurring incidents in LATAM and Southern-EU manufacturing SMEs.
  • Still circulating: as of Q2-2023, albeit at a slower, more targeted pace.

3. Primary Attack Vectors

  1. Phishing e-mails with ISO/IMG attachments → mounts a virtual drive to bypass Mark-of-the-Web → LNK shortcut executes PowerShell stager.
  2. Living-off-the-land lateral movement: uses Invoke-WMIExec/PsExec after harvesting credentials with Mimikatz.
  3. Exploits older, un-patched AD/ERP software:
  • CVE-2021-44228 (“Log4Shell”) in Java-based ERP web front-ends.
  • CVE-2021-34527 (“PrintNightmare”) for LOCAL-SYSTEM foothold on Windows servers.
  1. Exposed, brute-forced RDP secondary ingress when external 3389 is open; often preceded by dark-web purchased credential lists.

Remediation & Recovery Strategies

1. Prevention

  • Patch: Log4j (>2.17), Windows Print Spooler fixes, and all 2022-23 cumulative updates.
  • Disable RDP if not essential; otherwise enforce NLA + 2FA + IP allow-list + account lockout.
  • Disable Office→PowerShell/ISO-attachment execution through Group Policy ASR rules.
  • Segment LANs: separate ERP, OT, and user VLANs; use ACLs to block SMB/RPC crossing VLANs.
  • Deploy modern AV with behaviour-based engine (e.g., Microsoft Defender + network protection, or CrowdStrike, SentinelOne, etc.).
  • Immutable backups: 3-2-1 rule + “offline-copy” (disk-array or cloud-object with object-lock) that requires MFA to modify.

2. Removal (step-by-step)

  1. Physically isolate the infected machine(s) (pull cable / disable Wi-Fi).
  2. Collect logs (C:\Users*\AppData\Local\Temp*, PowerShell history, C:\Windows\System32\winevt\Logs) before purging—use write-blocker or mount disk read-only.
  3. Boot into Safe-Mode-with-Networking and run:
  • Malwarebytes 4.x or Kaspersky Virus-Removal-Tool → full scan → quarantine all hits.
  • Manually delete tasks labelled FilockRun, PowRun, or random-GUID found in Task Scheduler → \Microsoft\Windows\AppTask.
  • Remove registry autoruns (HKCU\Software\Microsoft\Windows\CurrentVersion\Run, RunOnce) pointing to C:\ProgramData\*.exe.
  1. Check persistence: clean WMI Event-Subscriptions (Get-WmiObject __EventFilter -Namespace root\subscription) and scheduled PowerShell run-keys.
  2. Reboot normally, verify network is still isolated; repeat scan until clean.
  3. Only re-join the domain after ALL DCs and remaining hosts have been verified clean (AV telemetry clear for >24 h).

3. File Decryption & Recovery

  • Decryptability: Files encrypted by Filock, at the time of writing, are NOT decryptable without the attacker’s private key. It uses Curve25519 + ChaCha20 + AES-256 in ECIES-like construction, eliminating practical brute-forcing.
  • Recovery paths therefore are:
  1. Restore from offline backups.
  2. Negotiation/payment (not recommended; no guarantee, funds criminal ecosystem, and may violate OFAC sanctions—victim due-diligence required).
  3. Shadow-copy check: Filock deletes \?*\GLOBALROOT\Device\HarddiskVolumeShadowCopy* but occasionally fails on multi-volume servers; run vssadmin list shadows and test with ShadowExplorer or icacls first.
  4. File carving/photorec: recovers original pre-encryption content only if disk sectors were not overwritten; works mainly for large media, not databases.
  5. Free decryptor: none available; ignore YouTube/“.filock-decryptor.exe” scams demanding further payment. Bookmark NoMoreRansom.org and Emsisoft Decryptors for authentic updates.

4. Other Critical Information

  • Double-extortion: before encryption, Filock uploads interesting file-types (contracts, NDAs, accounting archives) to Mega.nz using hard-coded API keys—expect data-leak pressure in ransom notes (HOW_TO_DECRYPT.hta).
  • Victim portal (.onion) assigns a 5-byte hexadecimal ID and offers a 1-file free decrypt “proof,” used to calibrate negotiation.
  • Infection marker: drops C:\Users\Public\Libraries\fk.lock – presence of this zero-byte file is an easy way for IR teams to confirm Filook vs. look-alikes.
  • Interop note: Filock uses Windows’ built-in wevtutil cl System to clear event log; hence gaps in System.evtx during incident timeframe are a red flag.
  • Wider impact: Although victim list is modest compared with LockBit, Filock actors hit mid-range manufacturers whose downtime cost is ~$50k-$70k per day—making >$1 M in aggregated revenue (Chainalysis 2023 crime report).
  • No macOS or Linux builds seen; purely Windows-focused.

Key takeaway: Because a working decryptor does not yet exist, the only reliable path is airtight backup hygiene plus the hardening checklist above. Isolate quickly, audit credentials, patch Log4j/PrintNightmare, and keep incident-response retainers or playbooks updated. Stay safe!