blackmatter

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: BlackMatter officially appends .blackmatter (in some campaigns .blm) to every encrypted file.
  • Renaming Convention: The malware first copies the victim’s hostname and time-stamp to the new filename, then appends the extension, e.g.
    Document.docx → hostname_2021-09-18_15-08-32.Document.docx.blackmatter

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First significant public sample(s) were submitted to VirusTotal on 27 July 2021. Large-scale intrusions were observed mid-August 2021 and continued through November 2021, when the group announced a voluntary shutdown of their Tor leak site.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Compromised credentials + Remote Desktop Protocol (RDP): Actor choice; once they obtain valid AD or local admin credentials they move laterally via RDP.
  2. Exploitation of unpatched vulnerabilities:
    • CVE-2021-20016 (SonicWall SMA100 SQL injection)
    • CVE-2021-34527 (“PrintNightmare” Windows Print Spooler)
    • CVE-2021-31207 (Microsoft Exchange ProxyShell chain)
    • CVE-2020-1472 (Zerologon Netlogon) – used to elevate to domain admin.
  3. Malicious e-mail attachments and links: Classic phishing with ISO or macro-laced Office documents acting as initial droppers.
  4. Purchased initial access: In several breaches analyzed, BlackMatter affiliates bought VPN or compromised RDP credentials from underground marketplaces/brokers.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Patch Priority: Immediately patch the Rapid7 “ProxyShell” triad (CVE-2021-34473, CVE-2021-34523, CVE-2021-31207) and apply the PrintNightmare cumulative (KB5005010+) and Zerologon patches.
  • Disable legacy protocols: Disable SMBv1 everywhere, enforce SMB signing, restrict NTLM if possible.
  • Restrict lateral movement:
    • Require MFA for all remote-desktop and VPN connections.
    • Create tiered admin model (Tier 0, Tier 1, Tier 2).
  • Network segmentation & outbound filtering: Block TCP/445, TCP/135 egress from non-authorised hosts, prevent WMI lateral abuse with host-based firewalls.
  • Email security: Remove .iso attachments at the gateway; require macro content to be signed and whitelisted.
  • Sub-minute backup schedule + immutable storage: Implement WORM (Write-Once-Read-Many) cloud snapshots or offline “cold” backups inside an air-gapped tape vault.

2. Removal

  • Infection Cleanup (Step-by-step):
  1. Isolate affected systems: Cut the NIC or disable Wi-Fi/BT; but do NOT power-off if you need forensic artifacts.
  2. Capture evidence: Create memory dumps (winpmem, Belkasoft RAM Capturer), then image system disks or at least collect master file table (MFT).
  3. Identify active persistence items:
    – Look for scheduled-task GUID with Base64-encoded rundll32 commands launching dllhost.dll in C:\Windows\System32\spool\drivers\color\ directory.
    – Check Registry HKCU\Software\BlackMatter and HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time-Protection.
  4. Delete the loader and dropped DLL: Generated mutexes contain BLACKM- prefix; kill corresponding dllhost.exe processes.
  5. Remove scheduled tasks & registry keys and nuke volume shadow copies (vssadmin delete shadows /all) only after you are sure you can trust the backups—BlackMatter clears them automatically.
  6. Run modern EDR/AV engine: Microsoft Defender with P2 EDR blocks BlackMatter (Sig 1.351.1.0+). Re-scan with offline boot media (CrowdStrike Falcon Live USB, Sophos Bootable AV).
  7. Verify integrity: Re-image or rebuild domain controllers from golden-image if compromise suspected.

3. File Decryption & Recovery

  • Recovery Feasibility: Public decryptor exists.
    In September 2021 a bug in the BlackMatter encryption routine was found by Emsisoft analysts. Emsisoft released a free decryption tool (v.1.0.0.24) that recovers data encrypted by BlackMatter up to v2.2.
  • How to use the decryptor:
  1. Download Emsisoft_Decryptor_for_BlackMatter.exe from https://www.emsisoft.com/ransomware-decryption-tools/blackmatter
  2. Launch as a local-admin user with network shares mapped (tool will iterate UNC/network drives).
  3. Provide a pair of encrypted & healthy files from the same folder so the decryptor can recover the file-specific encryption keys.
  4. De-select infected EXEs/DLLs to avoid false positives, then press “Decrypt”. Typical recovery rate ≈ 100 % if the files have not been overwritten post-encryption.
  • Essential Tools/Patches:
    • Windows cumulative update for PrintNightmare: September 2021 B-series (or later)
    • Exchange Security Updates August 2021
    • Microsoft Defender Antivirus: Update ~~platform 4.18.2108.x~~ or higher – sign. ver. 1.351.1.0+ adds BlackMatter signature.
    • Microsoft Defender for Endpoint behavioral rules: enable “Blocked ransomware behavior” Attack Surface Reduction (ASR) rule (GUID 01443614-cd74-433a-b99e-2ecdc07bfc25).
    • Rapid7 InsightVM / Nessus plug-ins to scan for targeted CVEs; free offline scanner: Nessus Home.

4. Other Critical Information

  • Unique Characteristics vs Other RaaS Families:
    • Uses Windows restart-manager API to terminate SQL Server, Oracle, MongoDB, MySQL, Veeam, and other business-critical processes before encryption, minimizing data corruption.
    • Contains large victim whitelist to avoid encryption in Russia, Ukraine, Belarus, Armenia, Moldova etc.; this is hard-coded in plain Russian language.
    • Offers victims a one-time negotiation chat over Tor; attackers typically demand 1-3 % of victim’s annual revenue.
    • Employs double-extortion model: they always steal data prior to encryption (via Cobalt Strike + Metasploit beacons), then threaten public release on their “Wall-of-Shame” leak site.
  • Broader Impact:
    – Hit critical infrastructure (New Cooperative feed provider, Olympus cameras, architecture firm Woods Bagot, U.S. Department of Agriculture co-op) and left farms without perishable animal-feed logistics.
    – Inspired later REvil / LockBit tactics; source code reuse with DarkSide is evident (50 % common functions).
    – Since November 2021 the gang pivoted its branding to BlackCat/ALPHV (Rust-based, .alphv extension), indicating a continuity—so some defenses learned here carry over.