acuna

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: acuna
  • Victims notice that every encrypted file is appended with the literal string .acuna after the original extension (e.g., Report_2024.xlsx.acuna, project.tar.acuna).
  • Renaming Convention:
    – The ransomware leaves the base filename and original extension intact, merely adding .acuna at the end.
    – No additional prefix or randomized component is inserted, so file lists are immediately recognizable after encryption.

2. Detection & Outbreak Timeline

  • First Public Sightings: May 2, 2024 (multiple submissions to public sandboxes and ID-Ransomware).
  • Rapid Escalation: Spiked between May 5 – May 10, 2024, hitting mostly small-to-medium businesses in Latin America and Western Europe through exposed SMB/RDP.

3. Primary Attack Vectors

  • Remote Desktop Protocol (RDP) brute-forcing – Most common entry path.
  • SMBv1 exploitation (EternalBlue-style techniques) – Second-tier propagation after the initial foothold.
  • Malicious email attachments (ZIP → ISO → MSI installer) that impersonate DHL & FedEx shipping updates.
  • Supply-chain abuse via pirated software bundles pushing cracked Adobe & AutoCAD installers.

Remediation & Recovery Strategies:

1. Prevention

  • Network & Authentication Hardening
    – Disable SMBv1 on every Windows host (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
    – Enforce MFA on every publicly accessible RDP endpoint; restrict it behind VPN or a ZTNA gateway.
  • Baseline Backups
    – Offline, encrypted backups (3-2-1 rule) performed daily; store at least one copy fully offline or in immutable cloud buckets (AWS S3 Object Lock, Azure Immutable Blob).
  • Email & Endpoint Control
    – Strip ISO/IMG attachments at the mail gateway.
    – Enable Windows AMSI & Microsoft Defender Exploit Guard; deploy application control (AppLocker / Windows Defender Application Control) to block unsigned MSI files.

2. Removal (Step-by-Step)

  1. Isolate & Quarantine
    – Disconnect affected machine(s) from both LAN/Wi-Fi and VPNs.
  2. Identify Persistence
    – Check Scheduled Tasks (schtasks /query /fo list /v) and Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) for entries pointing to %APPDATA%\AcunaUpdater.exe or similar.
  3. Terminate Malicious Processes
    – In Safe Mode, remove the main binary (usually %APPDATA%\Acuna\AcunaCrypt.exe) and accompanying DLLs.
  4. Registry & Service Cleanup
    – Delete service called AcunaShadowSync.
  5. Full AV/EDR Scan
    – Use updated Microsoft Defender (1.403.115.0+ signatures detect as Ransom:Win32/Acuna.A) or equivalent EDR (CrowdStrike Falcon, SentinelOne).
  6. Patch & Reboot
    – Apply KB5034441 (SMB fixes) and cumulative Windows updates, then return system to service.

3. File Decryption & Recovery

  • Current Status (June 2024): No known flaws in its ChaCha20+ECDSA encryption; free decryption is not yet available.
  • Recovery Options:
    – Restore from verified offline backups.
    – If backups are missing, target Volume Shadow Copies (ransomware only deletes them 20 % of the time); run vssadmin list shadows or use ShadowExplorer.
    – Check cloud sync folders (OneDrive, Google Drive) for file-version history which may survive encryption locally.
  • Essential Tools / Patches:
    – Kaspersky’s RannohDecryptor and ShadowExplorer (for shadow copy salvage);
    – Windows updates: KB5034441 (SMBv1 patches) and CVE-2024-30090 patch (privilege-escalation combo used by follow-up Cobalt-Strike beacons).

4. Other Critical Information

  • Unique Traits:
    – Drops a secondary backdoor (Backdoor.Win32.AcunaStealer) that commits to GitHub Gists for C2, bypassing some traditional DNS/IP monitors.
    – Timer starts at 96 hours rather than 72; every 24 h the decryptor price increases by 20 %.
    – Extensive file-type targeting (>4,800 extensions) including 3D model files (.blend, .obj) used in engineering firms.
  • Broader Impact:
    – Public-sector construction companies in Chile and Spain faced project downtime measured in weeks.
    – Over $2.2 M demanded collectively by end of May 2024, with low-payment rates (<3 %), indicating victims either restored from backups or data was non-critical.

Stay vigilant, keep backups airtight, and apply the hardening steps above promptly; at the time of writing, the only reliable way to retrieve .acuna encrypted data is through offline or immutable backups.