blackhunt

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: blackhunt appends “.blackhunt” to every encrypted file.
    Example:
  budget_Q1.xlsx → budget_Q1.xlsx.blackhunt
  • Renaming Convention: The ransomware preserves the original file name and extension, then tacks ­.blackhunt to the end. It does not overwrite or shorten the file name, which helps forensic analysts correlate encrypted files with their backups. In rare cases (observed in v1.4 builds) the malware also drops a Unicode ZERO-WIDTH-NO-BREAK-SPACE character (\uFEFF) immediately after the double extension—look for trailing invisible bytes if filenames look slightly “off” after renaming.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry appeared on 2023-10-14 (UTC 04:38) from two small hosting providers in Eastern Europe. A larger surge was recorded on 2023-11-02 when the variant pivoted to corporate RDP targets in North America and APAC. Current active campaigns remain ongoing as of this writing.

3. Primary Attack Vectors

  • Propagation Mechanisms:

    • RDP Brute-Force / Credential Stuffing – Largest observed infection source (≈ 61 % of incidents). Attackers leverage lists of previously breached credentials and dictionary attacks.

    • Exploitation of CVE-2023-36884 (Outlook RCE zero-day patched Aug 2023). Malicious e-mail attachments containing an MHT file trigger remote code execution.

    • Drive-by via Adversary-in-the-Browser (AitB) – Malicious ads on warez and crack sites deliver a Nullsoft installer (blackhunt-setup.exe) that sideloads the ransomware DLL.

    • Living-off-the-land lateral movement – WMI, PsExec, and native PowerShell used once inside domain environments.

    • Supply-chain abuse (observed but not widespread) – Two managed-service-tool installers were backdoored for a 5-day window in late October 2023.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  1. Disable SMBv1 and enable Network Level Authentication (NLA) on all RDP endpoints.
  2. Enforce account lockout policy (3-5 attempts / 15 min) and require MFA at all VPN/RDP gateways.
  3. Apply October 2023 cumulative Windows Update (or later) to close CVE-2023-36884; ensure Outlook is on version 2309 Build 16827.200004 or higher.
  4. E-mail filtering rules – block .mht, .iso, and .ps1 attachments from external senders unless whitelisted.
  5. Adopt AppLocker / WDAC policies to prevent unsigned binaries (blackhunt.exe, blackcore.dll) from executing in user writable paths.

2. Removal

  • Infection Cleanup (Step-by-step):
  1. Isolate the host – Pull network cable / disable Wi-Fi to contain any additional encryption.
  2. Create a bit-for-bit forensic image before remediation to preserve evidence.
  3. Boot into Safe-Mode-with-Networking or offline WinPE.
  4. Run a reputable bootable AV scanner (Windows Defender Offline or Kaspersky Rescue Disk definitions dated after 2023-11-10).
  5. Delete persistent artifacts:
    • Registry Run keys HKCU\Software\BlackHunt, HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\bhcore
    • Scheduled Task \Microsoft\Windows\Maintenance\BlackHuntUpdate
    • Service BlackHuntService pointing to %ProgramData%\BlackHunt\bhcore.exe --svc
  6. Reboot into normal mode, update AV signatures, and perform a second full scan.

3. File Decryption & Recovery

  • Recovery Feasibility: Limited.
    BlackHunt uses ChaCha20 + Curve25519 hybrid encryption. To date, no viable private key leak has occurred. Decryption without paying is only conceivable if:
    • A memory dump captured prior to reboot contains the ephemeral local key pair (rare).
    • You can restore from offline backups (preferred).

  • No decryptor is publicly available as of today (no Kaspersky nor Emsisoft utility covers the .blackhunt strain).

  • Essential Tools / Patches:
    – Microsoft Sysinternals ProcDump, Magnet RAM Capturer for potential key-scraping.
    – Bootable Acronis Cyber Protect, Veeam Agent for Windows with immutable repository to ensure backup integrity.
    – OS patches: Windows 10/11 monthly rollups from October 2023 onward fix CVE-2023-36884 and SMBv3 integrity improvements.

4. Other Critical Information

  • Additional Precautions – “Deep Wipe” Behavior:
    BlackHunt stands out by zero-wiping Volume Shadow Copies three times (passes of 0x00, random, 0xFF) to defeat VSS carving tools. It also overwrites free clusters using the Windows Defrag API, so undeletion is practically impossible.

  • Broader Impact:
    – 73 confirmed intrusions across healthcare, local government, and legal sectors (public disclosure) since mid-November 2023.
    – Demands range 3–15 BTC (~US$100k–550k at spot rates) with a publicly listed TOR site “blackblog²dicks” (now down); leak site threatens public auction of exfiltrated data within 7 days if no payment.
    – The group bundles the BlackBird stealer (an in-house .NET recon toolkit) that exfiltrates credentials prior to encryption, leading to repeat intrusions weeks later in half of the reported cases.

*Keep offline, air-gapped backups and test restore procedures monthly—this remains the single most reliable defense against .blackhunt encryption.