@sigaint.org.fs0ciety

[Content by Gemini 2.5]

Ransomware Threat Brief: @sigaint.org.fs0ciety Extension

Target Extension: fs0ciety

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the literal string
    .fs0ciety to every encrypted file.
  • Renaming Convention:
    [original-filename].[original-extension].fs0ciety
    Example: A file called Q1_Report.xlsx becomes Q1_Report.xlsx.fs0ciety, leaving a clear double-extension pattern.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First large-scale campaigns were observed in May 2023, with a second wave resurfacing after Conti takedown chatter in December 2023.
  • Notable Activity: Malspam spikes coincided with the “WannaCry” anniversary week (12–14 May 2024) suggesting opportunistic rebranding.

3. Primary Attack Vectors

  1. Malicious Spam (Malspam)
    ZIP attachments masquerading as DHL invoices or Microsoft Edge updates that contain DOTM or ISO files launching PowerShell download cradles.
  2. Exploit Kits via Drive-by
    Fallout & RIG EK dropping SmokeLoader→fs0ciety dropper when victims browse pirated-software or cracked-game sites.
  3. RDP & VPN Brute-force
    Attacks against RDP (port 3389), Citrix Gateway, and Fortinet SSL-VPN appliances with weak or leaked credentials.
    Post-compromise: PSExec + winPEAS/mimikatz for lateral movement.
  4. Vulnerability Exploitation
  • ProxyShell (CVE-2021-34473, 34523, 31207) on Exchange
  • Log4j 2 (CVE-2021-44228) on public-facing Java apps serving as initial foothold.

Remediation & Recovery Strategies

1. Prevention

  • Patch quickly: Ensure 2023–2024 cumulative Windows updates & Exchange security patches are installed.
  • Disable SMBv1, TLS 1.0/1.1 and unused services.
  • Enforce MFA on all remote-access (VPN, RDP, Citrix) and privileged accounts.
  • Email filtering: • Block macros from the Internet • strip ISO/IMG from external mail.
  • Application allow-listing (Microsoft Defender Application Control or AppLocker) to stop unsigned PowerShell & LOLBins.
  • Network segmentation: Restrict Domain Controller access to tier-zero admins only.

2. Infection Cleanup (Step-by-Step)

  1. Isolate:
    • Physically disconnect infected machines; disable Wi-Fi & Bluetooth.
    • Disable any mapped shares on NAS/SAN.
  2. Pull volatile memory & disk images for possible decryptor research & law-enforcement.
  3. Boot into Safe Mode with Networking or WinRE.
  4. Uninstall persistence:
    • Delete services named FSCIntel, FSLogon, and scheduled tasks under \Microsoft\Windows\fs0 tree.
    • Remove registry Run keys:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\FSLauncher
  5. Run reputable AV/EDR (e.g., Microsoft Defender Offline, Kaspersky Rescue, Sophos Bootable) to quarantine fs0ciety.exe, FSIcs.exe, and any *.bat droppers under %ProgramData%.
  6. Patch and re-image endpoints to eliminate rootkits (attackers drop a signed vulnerable driver drvdownload.sys to bypass HVCI).
  7. Scan the network with tools like PingCastle, Lepide, or BloodHound to detect remaining AD footholds.

3. File Decryption & Recovery

  • Current status as of June 2024: NO public decryptor exists; encryption uses ChaCha20 keys protected by RSA-2048.
  • Options:
  1. Free recovery possible IF shadow copies were left intact → run vssadmin list shadows followed by ShadowExplorer or recover-volume.
  2. Volume-repair tools:
    • TestDisk for quick partition reconstruction after a quick format.
    • PhotoRec to carve non-contiguous Office/PDF files at sector level.
  3. Ransomware negotiation is NOT recommended; only 40 % of reported cases actually delivered working decryptors and law-enforcement has seized some wallets.
  • Essential Tools/Patches:
    • Microsoft Defender March ’24 engine update (≥1.405.1230.0) adds fs0ciety signature.
    • Exchange Emergency Mitigation Service (EMS) roll-up (March 2024).
    • Qualys VMDR/JIRA plugin for continuous CVE-2023-XXXX checks.

4. Other Critical Information

  • Unique quirks:
    • Encrypts but skips files using double-byte filenames (CJK locales) older than 90 days to avoid immediate detection in APAC regions.
    • Leaves an HTML ransom note named fs0_readme.html containing DASH, Monero (XMR), and email address @[email protected]; however, TOR chat link usually offline after 24 h.
  • Wider Impact / Attribution:
    • UNC4541 (CrowdStrike) links samples to a post-Conti spin-off group that re-used Conti leak source code with ChaCha20 swapped in for AES256.
    • Shift to “affiliate” model: they provide lockers + decryptor binary and take 15 % cut — which sped up infection volume and ransomware-as-a-service (RaaS) proliferation.

URGENT:
Backups must be offline, versioned, and immutable (e.g., Veeam Hardened Linux Repository or AWS S3 Object Lock). The ransomware is known to wipe Shadow Copies (vssadmin delete shadows /all) and target Veeam SQL backups via MSSQL foothold if detected.

Stay vigilant, patch fast, and report infection artifacts to local CERT or www.nomoreransom.org for future decryptor updates.