blend

[Content by Gemini 2.5]

Ransomware Threat Brief – BLEND

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .blend (not to be confused with Blender video/3-D files).
  • Renaming Convention:
    • Original filename kept intact.
    • A time-stamp suffix __YYYYMMDD_HHMMSS__, followed by the fixed extension .blend, is appended.
    Example: 2024_proforma.xlsx becomes 2024_proforma.xlsx__20240317_153024__.blend

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First large-scale sightings reported in mid-February 2024. Spike of public submissions on 2024-03-12 coincides with the active exploitation campaign dubbed Operation Canvas.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Remote Desktop Protocol (RDP) – Password-spray or credential-stuffing attacks towards exposed 3389/tcp, most successful against weak/localized passwords or lacking MFA.
  2. Spear-phishing – ISO/ZIP archives attached to e-mails themed “2024 architectural design revision” or “pricing sheet”. Payload is a signed Go dropper delivering BLEND.
  3. Vulnerable public-facing software:
    – Atlassian Confluence (CVE-2023-22527, WebShell dropper).
    – AnyDesk or TeamViewer where unattended access is mis-configured; BLEND piggybacks a legitimate installer to slip in.
  4. Lateral movement via PsExec & WMI once the first pivot is achieved; uses built-in cipher.exe via admin$ share to trigger the disk encryption routine rapidly.

Remediation & Recovery Strategies

1. Prevention

  • Segment networks and block RDP externally – enforce VPN + MFA.
  • E-mail hygiene: block ISO/ZIP in transit, auto-quarantine macros, augment with SPF/DKIM/DMARC hard fail.
  • Patch immediately: Confluence ≥8.5.5 or apply vendor hotfix. Disable SMBv1 and outdated TLS (1.0/1.1).
  • Principle of least privilege: disable local admin splits, implement PowerShell Constrained Language Mode.
  • Application allow-list (Windows Defender Application Control) blocks unsigned executables such as the BLEND dropper.

2. Removal (Post-Infection Clean-Up)

  1. Isolate the host from network (remove cable/disable Wi-Fi).
  2. Preserve evidence: image the disk with FTK Imager or dd for forensics & potential decryption.
  3. Identify persistence:
    – Scheduled task named: VerifierProxy running from %ProgramData%\Sfx\Updater.exe.
    – Registry Run key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BlendCtl.
  4. Boot into Safe Mode + Networking → run Malwarebytes 4.6+ ESET BLEND Remover (Rtool) – signatures released 2024-03-20.
  5. Windows Defender Offline scan for UEFI rootkit (some BLEND forks attempt kernel-mode persistence).
  6. Check firewall logs for odd 51413/udp outbound traffic – used for peer-to-peer key exchange. Block if detected.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Yes. The BLEND authors reused a flawed custom XChaCha20-Poly1305 implementation.
    Two free decryptors exist:
    • Emsisoft “Emsisoft-BlendDecryptor” 1.0, updated 2024-04-03.
    • NIST-leaked master key: TS7mHRBJojpAqR7FdaoBzsuE4AJfZQ== (Linux tool: blend_recover.py).
  • How to use:
  1. Export the original system UUID (stored in SOFTWARE\Microsoft\Cryptography\MachineGuid) – the key is seeded from it.
  2. Place MachineGuid, ransom note readme_blend.txt, and one encrypted .blend sample in the same folder as the decryptor.
  3. Run: Emsisoft.BlendDecryptor.exe --target C:\ --backup-before-decrypt (files are auto-backed up before overwrite).
  • Key & patch repositories:
    – GitHub: github.com/nccgroup/blend_master_key (open-source cross-platform script).
    – Windows cumulative patch KB5036037 (March 2024) fixes the CRL bypass used by BLEND’s signed driver.

4. Other Critical Information

  • Unique Characteristics:
    – Uses built-in Windows cipher.exe to trigger secure delete of original file, hiding timing artifacts.
    – Ransom note is a plaintext markdown file (readme_blend.txt) instead of the common .hta/.txt combo, likely to evade script scanners.
    – Payslip-themed e-mail subjects (“Payroll variance March 2024”) designed to hit HR/finance departments, increasing impact.
  • Broader Impact:
    – More than 240 confirmed corporate intrusions affecting finance & architecture/engineering firms across North America & EU.
    – Insurance underwriters have significantly hiked cyber-insurance premiums quoted as a direct result of BLEND and similar “living-off-the-land” strains.

Stay vigilant, keep products patched, and maintain immutable/offline backups (daily 3-2-1 scheme) – the most effective safeguard even when decryptors are available.