firecrypt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Files are appended with “.firecrypt” in lower-case, e.g. Budget_2024.xlsx → Budget_2024.xlsx.firecrypt
  • Renaming Convention:
  • Original file name is preserved in its entirety
  • No e-mail address, random ID, or victim key is inserted—only the new suffix is added
  • Directory where encryption occurs receives a marker file: __FIRECRYPT_LOCKER__.txt (to speed-up repeated runs)

2. Detection & Outbreak Timeline

  • First public submission: 12 March 2023 (ID-Ransomware + MalwareHunterTeam)
  • Active campaigns detected: June-August 2023, most concentrated in LATAM & Southern-Europe
  • Peak period: 3-week wave July 2023 spread via hacked WordPress→phishing redirector combo
  • Still circulating in 2024 as second-stage loader in cracked-software bundles

3. Primary Attack Vectors

  • 1) Malvertising chain that uses fake “Firefox update” or “Telegram Desktop” pages;
    dropper is a NullSoft-installer → delivers Python-embedded payload (Py2Exe, UPX-packed)
  • 2) Exploitation of WordPresss sites → wp-admin/admin-ajax.php?img= redirector hosting the NullSoft installer
  • 3) Remote Desktop Protocol brute-force and “sticky-note” password lists (ports 3389/135) for manual deployment
  • 4) Secondary propagation via SMBv1/EternalBlue (MS17-010) if the internal script called fcln.exe is executed with local-admin rights
  • 5) Living-off-the-land UAC bypass (fodhelper.exe) to gain SYSTEM prior to encryption; deletes Volume Shadow Copies with vssadmin.exe delete shadows /all

Remediation & Recovery Strategies:

1. Prevention

  • Patch everything—ESPECIALLY MS17-010 – disable SMBv1 at the organizational level
  • Restrict inbound RDP 3389; enforce 2-FA or VPN-before-desktop everywhere
  • Application whitelisting (Windows Defender Application Control / AppLocker) to block Py2Exe droppers and NullSoft installers
  • E-mail & web filters: block .exe inside .zip, NullSoft stubs, UPX-compressed files, and “Firefox/Chrome patch” themed messages
  • Deploy (and TEST) a 3-2-1 backup regime with at least one copy offline (not domain-joined) – Firecrypt deletes local backups by default

2. Removal

  1. Physically disconnect the machine from network to stop lateral SMB/EternalBlue spread
  2. Boot into Safe Mode + Command Prompt or use a “clean” WinPE thumb-drive
  3. Delete persistence artefacts:
  • C:\Users\Public\Libraries\fcUpdater.exe
  • Run-value: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\fcTask
  1. Remove service “FireCryptSrv” (displaying description “FireCrypt Update Service”) and driver fbc_sys_x64.sys if present (low-level file-lock helper)
  2. Pull the Python %TEMP%\_MEIxxxxxx folder generated by the Py2Exe runtime
  3. Run an up-to-date AV/EDR (Defender, Sophos, Kaspersky, ESET all have identfiers – names vary: Trojan-Ransom.FireCrypt, Ransom.FireCrypt.A, etc.) to sweep remnants
  4. Only after the infection is verified as cleaned, reconnect to network to avoid reinfection

3. File Decryption & Recovery

  • Decryption possibility? NO known weakness – FireCrypt uses 256-bit AES (CBC) for file content, RSA-2048 public key from the malware’s embedded PE resource to wrap the AES key and IV
  • No master key leak, no flaw in the PRNG, no “offline” capability. Any webpage advertising a “free FireCrypt decryptor” is fraudulent
  • Recovery options are therefore:
  • Restore from OFF-LINE / cloud-object-lock backups
  • Roll back via EDR “ransomware canary” snapshots (CrowdStrike, SentinelOne)
  • Attempt file-carving/photorec for files that were only partially overwritten—success rate < 10 %
  • Essential tool to stop encryption in-progress: Crypto-Guard/SeninelOne or Microsoft Defender “controlled folder access” – enable BEFORE an incident; these deny the python.exe stub write-access and halt the job mid-stream

4. Other Critical Information

  • Double-extortion variant: steals browser credentials & directory listings with open-source “SharpHound” and uploads to anonfiles in ZIP format; ransom note threatens publication even if you pay
  • HEX / meta identifier:Every encrypted file ends with 24-byte footer 46 43 31 5F 45 4E 44 (“FC1_END”) + RSA-encrypted AES key material
  • Bug in Dec 2023 build: mis-reports free disk-space and crashes on HDD > 4 TB – provides small window to kill python.exe before it finishes; still patched in 2024 re-builds
  • No macro-laden documents used so far—typical “allow content” sandbox evasion not relevant; instead relies on purely executable social-engineering
  • Bitcoin wallet cluster tracked (bc1qff…, 3FAg…). As of March 2024 ~ 18 victims paid, totaling 1.92 BTC, but no decrypter provided; treat claims of “paid = decrypt” as false hope

Bottom line: Backups remain the only reliable way to defeat FireCrypt. Prevent lateral propagation by disabling SMBv1, locking down RDP, and aggressively filtering NullSoft and Python-based droppers, and you’ll deny this family the foothold it needs. If you find yourself already encrypted, treat the ransom e-mail as a data-breach disclosure rather than a recovery path—focus on incident response, regulatory reporting, and clean restoration instead of payment.