fcrypt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The “fcrypt” strain appends “.fcrypt” as a 6-byte, lower-case extension to every file it encrypts (e.g., Invoice.xlsx → Invoice.xlsx.fcrypt).
  • Renaming Convention: In addition to the new extension, the malware often rewrites the original file name with a “marking” structure:
    [original name][original extension].fcrypt
    This keeps the old name visible (which helps the note look legitimate) while still producing a clear ransom flag.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public samples and victim forum reports appeared in April 2019, with a larger wave reported in Q3–Q4 2019.
    Occasional “spin-off” campaigns (same builder, different distribution affiliates) were seen through 2020–2021, but primary volume subsided after spring 2020.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Malicious spam delivering a first-stage .JS, .VBS or macro-laced Office document; when enabled, the script pulls the 32-bit C++ “fcrypt” binary from a hacked web server.
  • Exposed RDP (port 3389): brute-forced or credential-stuffed logins remain the second most common entry point. Once inside, attackers manually drop the ransomware.
  • Pirated software bundles / keygens / fake “cracked” game installers masquerading as the ransomware dropper.
  • No evidence of worm-like SMB exploits (EternalBlue, etc.); infection is typically “hands-on keyboard” by affiliate actors or through user-executed trojans.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Segment LANs; block smb/tcp 445 between user VLANs if not explicitly required.
  • Disable RDP from the Internet or place it behind a VPN with MFA.
  • Enforce strong, unique passwords and lockout policies for RDP/local admin accounts.
  • Patch OS & third-party software—fcrypt often arrives after initial loaders exploit older Office or PDF flaws.
  • Deploy application whitelisting (Windows Defender Application Control / AppLocker) to prevent unsigned binaries from executing under %TEMP%.
  • Maintain 3-2-1 backups (3 copies, 2 different media, 1 off-line/off-site).
  • Disable Office macros by GPO; block executable content in mail gateways (*.js, *.vbs, *.wsf, etc.).

2. Removal

  • Infection Cleanup:
  1. Power-down but do NOT reboot the machine yet – some variants overwrite MBR if you reboot without paying.
  2. Boot from clean WinPE / Linux USB and back-up the encrypted volume’s MFT/shadow copies before any further writes.
  3. Re-image the system from known-good media (or restore from pre-infection snapshot) and DO NOT reconnect to production network until patched & AV/EDR installed.
  4. Scan adjacent machines with reputable EDR (Defender, CrowdStrike, SentinelOne, etc.).
  5. Change all local/domain credentials the infected host cached.

3. File Decryption & Recovery

  • Recovery Feasibility: Fcrypt uses Curve25519 + AES-256 in ECB for each victim (random session key, public-key encrypted). No design flaw or leaked master key has surfaced; therefore DECRYPTION WITHOUT THE ATTACKER’S PRIVATE KEY IS CURRENTLY NOT POSSIBLE.
  • There is no free public decryptor.
  • You can:
    – Restore from offline backups;
    – Check Volume Shadow Copies (vssadmin list shadows) – some early samples forget to delete them;
    – Scrape free recovery tools (PhotoRec, EaseUS, R-Studio) to retrieve deleted originals IF the malware only copied/encrypted rather than safe-wiped originals.
  • Essential Tools/Patches:
  • Windows 10/11 fully patched (ESU for Win7).
  • Office 2016/2019/O365 with macros disabled.
  • Up-to-date endpoint protection (Microsoft, Kaspersky, ESET, Sophos all have fcrypt signatures).
  • BitLocker or credible data-at-rest encryption does NOT help against ransomware (already running with your privileges) but does stop thieves who physically steal drives.

4. Other Critical Information

  • Additional Precautions & Traits:
  • Drops ransom note “# fcrypt-DECRYPT.txt” (sometimes “# DECRYPT MY FILES #.txt”) in every folder and on the desktop; content is frequently in broken English demanding 0.08–0.15 BTC to a static wallet that changes per campaign.
  • Deletes local shadow copies via vssadmin & wbadmin, disables Windows recovery, and turns off the firewall to aid lateral movement by affiliates.
  • Does not target critical system files (.exe, .dll, .sys) because it needs the machine functional to display the ransom note—works off a “whitelist” of ~190 extensions.
  • Early builds appended “_locked” before “.fcrypt”, which can confuse triage—still the same family.
  • Broader Impact:
  • Primarily slammed small–medium businesses (architecture firms, dentists, small municipalities) that relied on single on-premise servers with an external RDP port.
  • Average “ask” was modest, resulting in a higher percentage of victims paying—feeding an affiliate ecosystem and inspiring copy-cat builders that retained the “.fcrypt” branding even when keys changed.
  • No evidence of data exfiltration; focus is purely destructive/encryptive—but affiliates routinely stage Cobalt Strike beacons first, so assume compromise of all data stored on the machine.

Bottom line: There is no shortcut to unlock “.fcrypt” outside of the criminals’ key. Robust, isolated backups and hardened RDP/macro hygiene remain the only reliable ways to bounce back without funding the attackers.