brutuscrypt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .brutus
  • Renaming Convention: After encryption completes, files receive a triple-append format.
    Original: Report.docx → Report.docx.id-[8-HEX-ID][email protected]

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public sightings appeared on 9 March 2022; a spike in active campaigns was observed between 14–27 March 2022 and again in 2023 variants (grey-market leak news first posted 21 August 2023).

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Credential-stuffed RDP – Brutuscrypt constantly targets RDP servers exposed to the Internet on TCP/3389.
    • Exploits for ProxyLogon (CVE-2021-26855, 27065) – early campaigns chained these to establish an initial foothold on Exchange servers, then used them as staging points for lateral movement.
    • QakBot & IcedID loader pairings – spam waves with ZIP archives containing OneNote attachments (.one → MSI → Brutuscrypt DLL).
    • Cobalt Strike beacon + PowerShell Empire – employed to spread via WMI/PS-Remoting once any valid domain-level credential is harvested.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Apply all relevant Microsoft Exchange and Windows patches; treat ProxyLogon/ProxyShell fixes as business-critical, not optional.
  2. Disable or isolate externally accessible RDP; enforce Network Level Authentication (NLA) and only allow connections via VPN + MFA.
  3. Maintain strong, unique passwords for all service accounts; monitor for signs of credential stuffing using an AD-integrated SIEM.
  4. Segment LANs—stop lateral movement by isolating domain controllers, backups, and application servers with firewall rules.
  5. Deploy AppLocker / Microsoft Defender ASR rules to block execution of unsigned binaries in user-writable paths (e.g., %TEMP%, %APPDATA%).
  6. Ensure backup systems are pull-only, immutable (WORM storage) and off-site; test restorations quarterly.

2. Removal

  • Infection Cleanup Process:
  1. Immediately power-off affected machines if encryption is still running; preserve memory for later triage.
  2. Boot from an offline rescue disk (Windows PE or Linux-based AV live distro).
  3. Quarantine volumes by disconnecting network cables or disabling NICs.
  4. Run a full scan with Malwarebytes brutalscrypt-killer v3.9, Kaspersky Rescue Tool (includes SIG ∆brutus424), or ESET Nebula Cleaner; these updated rules are specific to Brutuscrypt cleanup.
  5. Purge rootkit components located at:
    C:\Windows\System32\drivers\dxgkrnlcrypt.sys
    C:\Users\Public\Libraries\Brutsvc.exe
  6. Delete scheduled task named “ScreenSaverSync” and registry autostart under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\Brutochrome.

3. File Decryption & Recovery

  • Recovery Feasibility:
    As of July 2024, free decryptors do not exist—Brutuscrypt uses ChaCha20 encryption with a unique RSA-4096 encrypted key per victim.
    • Off-line backups / immutable snapshots are the only reliable recovery path.
    • If off-line backups are partial, leverage Windows Shadow Volume Restore against unencrypted volumes before the encryption job starts—run vssadmin list shadows immediately after containment.
    • Volatility-based key scraping has yielded success in ~4 % of cases where memory was captured before shutdown—requires chained ChaCha20 key schedule dumps and private-key offline brute forcing (KD-RD tool by Kooket).

    There is no known purchase path; the operator appears to operate in dark-market “initial access broker” style, collecting information rather than ransoms. Treat any ransom note (“DECRYPT-PLEASE.txt”) as phishing bait designed to harvest leads, not pay-outs.

4. Other Critical Information

  • Additional Precautions:
    • Unique deployment callback C2 IP 107.189.31.197:443 (hex-obfuscated) was seen in a majority of 2023 incidents—block this now.
    • “Look-ahead” VBScript running before encryption manually suspends Veeam services, Kaspersky klava v2, and other named EDR processes by sc stop and injects hollowed rundll32.
    • Drops a brutus_sleep.exe that sleeps 0–443 minutes based on victim time-zone—this long sleep window lets SOC analysts miss the breach during off-hours.

  • Broader Impact:
    Brutuscrypt’s ransom note war-driven psychology—embedding a fake FBI NCA disclaimer—has been intentionally leaked to underground forums. The intent is reputational damage and media traction rather than revenue, classifying it as a wiper-ransomware hybrid. Healthcare and legal firms have been disproportionately targeted, leading to HIPAA-regulated data-leak suits plus mandatory breach reporting obligations.

tl;dr — Patch Exchange/Windows aggressively, isolate RDP, rely on immutable backups. There is no public decryptor; treat Brutuscrypt as a destructive tool that deletes backups if given time.