blacksuit

[Content by Gemini 2.5]

Technical Breakdown: BlackSuit Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Encrypted files receive the suffix .blacksuit (lower-case).
  • Renaming Convention:
    – Original: Annual_Report.xlsx
    – After encryption: Annual_Report.xlsx.blacksuit
    – Same pattern for folders: a plaintext ransom note (README_TO_RESTORE_FILES.txt or RECOVER-blacksuit.txt) is dropped into every affected directory.
    – Certain new BlackSuit droppers also prepend the victim identifier to each file name (e.g., C-1234_Annual_Report.xlsx.blacksuit) when exfiltration data has been confirmed (dox operation).

2. Detection & Outbreak Timeline

  • First Public Sighting: May 2023 (containment began mid-May, but telemetry spikes strong on 24 May 2023).
  • Active Surge: June-Aug 2023 became its largest infection wave (esp. healthcare & higher-ed).
  • Recent Variants: Minor iterations seen up to March 2024 (primarily new onion domains & improved speed in file encryption).

3. Primary Attack Vectors

  • Remote Desktop Protocol (RDP) brute-force / credential-stuffing – Single largest ingress (~60 % of incidents).
  • CVE-2023-0669 (Fortra GoAnywhere MFT pre-auth RCE) – Used by affiliates for large enterprise footholds.
  • Valid API keys & application credentials exfiltrated from prior info-stealer infections (Raccoon, Vidar, Lumma) to move directly into cloud file-shares without lateral traversal.
  • Phishing + ISO/LNK payload (mimics invoice or subpoena attachments). When executed, drops BlackSuit core DLL (usually x64).
  • Malvertising campaigns redirecting to exploit kits patched in June-2023; now in decline but still seen in older Chrome/Edge browsers.

Remediation & Recovery Strategies: BlackSuit

1. Prevention

  • Immediate blocks:
    – Disable or restrict RDP to VPN-only; enforce IP allow-lists & MFA.
    – Deploy EDR with ASR rules “Block credential stealing” & “Block process injection”.
    – Segment networks: put DMZ file-transfer servers (GoAnywhere, FileZilla, IIS) in their own VLAN—no direct SMB access to production fileservers.
    – Filters/O365 rules: block incoming archives that contain .iso, .img, .lnk, .vhd extensions pre-delivered.
    – Regular offline (immutable) backups at least 3-2-1 model—test restore monthly.
  • Patch cadence:
    – Apply GoAnywhere 7.4.1+ (patch released 17 Feb 2023).
    – Pick up the March 2023 cumulative Windows Security Update to silence any remaining PrintNightmare edges.

2. Removal

  1. Evidence preservation: Isolate, but do not shut down; snapshot RAM before pulling power.
  2. Stage 1 – Containment:
    – Disconnect host from network/Wi-Fi.
    – Suspend all privileged service accounts whose passwords may have been scraped.
  3. Stage 2 – Forensic identification:
    – Look for:
    %TEMP%\****__random_dll_payload.dll (64-bit) invoked by rundll32.exe or regsvr32 /i BlackSuit64.dll.
    Scheduled task named “ServiceBroker” or “WusaUpdate” (typical autostart keys).
  4. Stage 3 – Eradication:
    – Boot from offline media (Windows PE) → run Kaspersky Rescue Disk 18 or Bitdefender Ransomware Remediation Toolkit to quarantine the dropped DLLs plus registry persistence entries.
    – Once offline → wipe only system partitions. Reimage; do not restore user profile or %APPDATA% dirs yet (in case residual stealers).

3. File Decryption & Recovery

  • Recovery Feasibility (Aug 2024 status): No publicly-viable decryptor yet. BlackSuit employs Curve25519 (victim key pair) + AES-128 CTR; the private key is offline at attacker’s side.
  • Pay-or-Restore: Refuse to pay? Your only route is backups, volume-shadow copies (if not wiped), or creative recovery through mail-item stems.
    – Check VSSAdmin list shadows — in ~15 % of incidents an early kill-switch saved at least a few shadow drives.
    – Try Kroll Recovery Explorer (forensic undelete) where the malware’s “-Wiper” switch appears to scavenge MFT instead of secure-wiping.
  • Essential Tools / Patches:
    – Detection by AV signatures:
    • CrowdStrike Falcon “Ransom.win.BLACKSUIT.C”
    • SentinelOne for Mitre T1486 (tamper-protected recovery backups)
      – Vendor-provided patches:
    • Fortra advisory FA-20231201 – hot-fix for CVE-2023-0669.
      – NirSoft ShadowCopyView (portable) – quick sanity check before wiping drives.

4. Other Critical Information

  • Distinguishing Traits:
    – “Double-extortion” model: steals data via Rclone or age-encrypted ZIP before encryption, exfiltration to Mega.nz, File.io, and paid proxies/reseller TDS.
    – Linux variant ELF/BlackSuit targeting ESXi & NAS – uses /usr/bin/dd if=/dev/zero + sponge alternately for performance.
    – Ransom demand UI on Onion site is branded “BlackSuit Leaks” and includes a countdown timer + partial leak tree (typical 1 GB share preview).
  • Risk of clean-sets furious: BlackSuit now auto-executes disk-limited “-cyberwipe” switch if it detects certain EDR filenames (crowdsec.exe, cb.exe, sentinelctl.exe)—so removal strategy must be complete before first reboot.
  • Sector Impact:
    – U.S. & U.K. healthcare: disclosed downtime averaging 12.7 days.
    – Higher-ed & MSPs: significant SME helpline uptick—demand median $4.7 M USD (trend Q2 2024).

Deploy the playbook above and continue to monitor the usual threat-intel feeds (#BlackSuit, @intelX_trade). Stay safe & share IOCs responsibly.