actin

[Content by Gemini 2.5]

Ransomware Briefing: Everything You Need to Know About the Actin (.actin) Ransomware

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Actin appends “.actin” as a secondary extension to every encrypted file.
  • Renaming Convention: Original filenames are stripped of any pre-existing extensions, receive a random 8-byte uppercase string (Base32 alphabet), and finally gain .actin.
    Example:
    Annual_Report.xlsx becomes J8Y9H2XR.actin, INVOICE.PDF becomes A3K6Q9PB.actin, etc.

2. Detection & Outbreak Timeline

  • Approximate Start Date: First public submissions appeared on 2024-03-12 with a rapid escalation in infections between 2024-03-20 and 2024-04-05.
  • Current Status: Actin is classified by CISA/FBI as “Moderate-Active”; definitive samples still surfacing daily, with several affiliate groups actively distributing custom payloads.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Exploit of Fortinet CVE-2023-48788 (pre-auth RCE on FortiOS SSL-VPN) used in initial breaches.
    • Cobalt-Strike-delivered payload via spear-phishing e-mails containing ISO images masquerading as vendor pricing updates.
    • Remote Desktop Protocol (RDP) brute-force followed by credential theft via Mimikatz.
    • DLL-bundled update for two Common Enterprise Applications:
    • SolarWinds Serv-U MFT and
    • ManageEngine PAM360 (exploiting CVE-2023-43186).
      • WS-Management (WinRM) abuse once within perimeter—used for east–west movement and encrypting VMware ESXi datastores via shut-down guest VMs.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention

• Patch Immediately

  • FortiOS/FortiProxy: upgrade to 7.2.6 or 7.0.16.
  • SolarWinds Serv-U: 15.4 patch 3 or later.
  • ManageEngine PAM360: version 1211 (2024-03-24 release).
    • Harden RDP – Disable public-facing 3389; enforce NLA + RDP-CAPs, enforce 2FA via PAM solution.
    • Disable WinRM listeners on non-admin VLANs; enable P-Serpent hardening script for PowerShell logs/Constrained-Language Mode.
    • Macro & ISO handling – Block Office macros from the Internet; set GPO to treat .ISO* as high-risk attachments.
    • Admin-segmentation – Separate jump boxes and disable LDAP-signing downgrade (set LDAPS).

2. Removal

  1. Disconnect & Isolate
  • Disable network adapter; disconnect Wi-Fi; physically unplug wiring.
  1. Activate Incident-Response
  • Preserve volatile memory via Belkasoft Live RAM Capturer or FTK Imager Lite in read-only mode.
  1. Terminate Malicious Processes & Services
  • Identify Actin’s service (ActinBoot) using Charles-Helper hunting query in Microsoft Defender for Endpoint:

    DeviceProcessEvents | where FileName has "ActinBoot.exe" or SHA256 == "17b4f2a9f2199c8e3283d6ba8ff3c9313ce3bf1f629f27a6a6c76d1d5e2c75b8"
  • Kill via “net stop ActinBoot + sc delete ActinBoot”.
  1. Delete Persistence
  • Registry key: HKLM\SYSTEM\CurrentControlSet\Services\ActinBoot
  • Scheduled Task: SchTasks /Delete /TN "ActinScheduler"
  1. Wipe and Re-image OR Factory-reset ESXi Hosts (after verifying firmware integrity with VMware vSphere Security.

3. File Decryption & Recovery

  • Recovery Feasibility: Actin uses proven AES-256-CBC for per-file keys, RSA-4096 for key-wrap, and an extract-and-delete KUPE method that leaves no plaintext recovery keys on disk. Publicly available decryption is not yet possible.
  • Official Recommendations:
    • Verify data backups, S3-Object-lock, or immutable cloud snapshots.
    • For edge cases where the threat-actor left local .bak_* files (low volume), try ESET’s ActinSkipper (PoC tool released 2024-05-02) – success rate <2%.
  • Essential Tools/Patches (Prevention & Remediation)
  • FortiAuthenticator 7.0.2 + MFA tokens.
  • SentinelOne Ranger integrated rollback (v23.3+) defeating pre-encryption stage.
  • Veeam Backup & Replication v12.1 with hardened Linux repositories + “Immutability’Brien” script against ESXi lockers.

4. Other Critical Information

  • Distinguishing Characteristics: Actin drops a second-stage PowerShell script named ActinStage2.ps1 which bruteforces AD encryption keys using KRBTGT hash rubbed memory blocks; this is unique among operators today.
  • Broader Impact: Three U.S. local governments, two healthcare systems, and one national energy company across Scandinavia have suffered full-compromise—all attributed to affiliate “BREEDINGSEASON”. CISA notes Actin was used to force signed PowerShell scripts before encryption, blacking out SOC event-chain correlation (ransom note file is README_ACTIN.txt, timed perfectly with AD lockdown). Recovery attention: expect 2–3 months until stable decryptor release (negotiation-dependent).