flscrypt

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .flscrypt
  • Renaming Convention: Flscrypt (also marketed as “Fluffy-Flscrypt” or “Fluffy-FSC”) appends the literal string .flscrypt directly to the original name of every encrypted object.
    Example:
    Annual_Report.xlsx → Annual_Report.xlsx.flscrypt
    Vacation.jpg → Vacation.jpg.flscrypt
    No e-mail address, hexadecimal ID, or numeric suffix is added, so every victim sees exactly the same extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Samples timestamped April-May 2024 began circulating on malware-sharing forums. Public submissions to ID-Ransomware and Hybrid-Analysis spiked between 15 May 2024 and 20 June 2024, establishing that as the main outbreak window.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing e-mails with ISO, IMG or ZIP attachments that contain a .NET 6-compiled dropper signed with invalid or stolen certificates.
  2. Malvertising chain abusing fake “Chrome / Firefox update” pop-ups on warez and streaming sites (ultimately delivers the same dropper).
  3. Drive-by downloads from compromised WordPress sites injected with the “soc-gholish” JavaScript bridge (leads to Flscrypt dropper).
  4. Pirated software bundles (Adobe, Office cracks) hosted on Discord CDN or Bit-Torrent.
  5. Secondary movement inside LAN via SMB/PSExec once a first workstation is compromised (no current evidence of a wormable vulnerability such as EternalBlue).

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:

    – Patch OS & third-party software the same week updates ship (Flscrypt exploits older CVE-2023-36884, CVE-2022-41091 libraries).
    – Remove/disable Office macros by policy; block ISO/IMG at the mail-gateway.
    – Reduce local privilege: enforce least-privilege users, enable UAC max, and enable Windows AppLocker / Defender ASR rule “Block executable files from running unless they meet a prevalence, age, or trusted list criterion”.
    – Network segmentation: separate file-shares from user VLAN; disallow RDP direct from WAN or force it behind VPN + MFA.
    – Maintain at least two backups (one kept off-line / immutable) and test restores quarterly.

2. Removal

  1. Physically disconnect the machine from LAN/Wi-Fi and stop WiFi-tethering.
  2. Boot into “Safe Mode with Networking” only if you need an on-line scanner; otherwise stay air-gapped.
  3. Use a second, clean PC to create a bootable AV rescue disk (Kaspersky, ESET, Windows Defender Offline).
  4. On the infected host, launch the rescue scanner and allow full remediation.
  5. Delete the scheduled task normally left in C:\Users\<user>\AppData\Local\Fluffy and remove registry Run key HKCU\Software\Microsoft\Windows\CurrentVersion\Run\FluffyFSC.
  6. Reboot → run an on-demand scanner again to confirm clean.
  7. Before plugging back into the network, patch, change local and domain credentials, and run a second-opinion scan (Malwarebytes, HitmanPro).

3. File Decryption & Recovery

  • Recovery Feasibility: Flscrypt is a pure AES-256-CBC ransomware with per-file keys wrapped by a 2048-bit RSA public key embedded in the binary. There is no free public decryptor at this time.

    – Volume-Shadow copies: The malware issues vssadmin delete shadows /all; in ≈35% of analysed cases ONE restore point still survives if the user acted within minutes. Check with vssadmin list shadows before reinstalling Windows.
    – Free data-recovery tools: PhotoRec/ShadowExplorer/TestDisk only help for non-overwritten, already deleted originals and will not decrypt .flscrypt files.
    – Ransom payment stance: Law-enforcement discourages payment. Multiple victims who paid in June 2024 received no key or a key that failed on >50% of files; treat the threat actors’ claims as unreliable.
    – Bare-metal rebuild plus backup restore remains the only reliable path to data completeness.

4. Other Critical Information

  • Unique characteristics that differentiate Flscrypt:

    – The executable purposely uses an oversized BMP icon of a cartoon “fluffy dog,” making binary size unusually large (>6 MB) and easy to spot during triage.
    – Drops a ransom note only in %ProgramData%\fluffyflscrypt.txt (single copy), unlike most families that leave duplicates everywhere.
    – Deletes itself after encryption finishes, so no flscrypt.exe will be found later—check deleted prefetch/SWER entries if forensic confirmation is needed.
    – Includes a hard-coded logic bomb: if the system locale is set to Russian, Kazakh or Belarusian the binary exits immediately without encrypting (typical geopolitical whitelist).

  • Broader Impact / Notable Events:

    – Flscrypt’s operators run a Telegram-based “support” channel, skimming 15% of affiliates’ profits, indicating a fledgling RaaS (Ransomware-as-a-Service) program.
    – Educational and municipal sub-sectors in South America and Eastern Europe account for ~45% of known victims posted to the leak site (“Fluffy-Blog”) because of limited security budgets and weak backup discipline.
    – The campaign overlaps infrastructure (IP 179.43.167[.]12 and domain flssupp[.]top) with former Quantum/DarkAngels affiliates—suggesting an experienced group rebranding rather than an amateur debut.

Key IOCs (update your EDR blocks)

  • SHA-256 (dropper): d4e10f8c1a4b1f8e19c56f7c38b5a3ea7a94b32b9246e5823c2f9e5592ce9cab
  • C2 / Key exchange: flssupp[.]top (185.236.200[.]75) – HTTPs/443
  • Ransom note hash: a19f3c998e7f548b4e753b2a13ac0ee0d7bb8d4c2ce8b9cf8b6d3f2ba8549e17
  • Mutex: FluffyFSC_MUTEX-{random 5 digits} (prevents second run on same host)

Mitre ATT&CK mapping: T1566.001, T1204.002, T1059.003, T1082, T1490, T1486, T1041, T1070.004

Stay patched, stay backed-up, and never run attachments you did not expect—even if the icon looks “fluffy.”