alma locker

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: ALMA Locker appends the suffix “.locked” to every encrypted file.
  • Renaming Convention: The malware does not alter the original filename or its path; it simply adds “.locked” to the end (e.g., Report.xlsx.locked, photo.jpg.locked). Directory names are left untouched.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First substantial alerts surfaced late-January 2023 (major spike 2023-01-25 → 2023-02-05). A secondary wave targeting NAS devices was observed mid-May 2023.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Phishing email attachments or links – CHM and ISO archives masquerading as invoices/purchase-orders.
    • Inventory/DCE-RPC brute-force & RDP compromise – automated attacks against exposed RDP on port 3389; note that an uptick in Log4Shell (CVE-2021-44228) was leveraged to drop the ALMA payload on vulnerable Web applications.
    • Supply-chain infection – a mis-configured software-update mechanism was manipulated to push a malicious patch (.MSI) down-stream to end-users (documented March 2023).
    • Lateral movement via PSExec/WMI once an initial endpoint is infected.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures
  1. Harden external access: Disable RDP for WAN / restrict to VPN, require Network Level Authentication (NLA) and strong, unique credentials.
  2. Email filtering & user training: Block inbound CHM, HTA, ISO and archive attachments if unused; enable SPF/DKIM/DMARC.
  3. Patch stack: Prioritize Log4j fixes on Java-based applications, apply the latest cumulative Windows security updates.
  4. Application whitelisting: Approve-list only endorsed executables (WDAC, AppLocker, or equivalent policy-based control).
  5. Tiered backups: 3-2-1 rule with at least one set offline / immutable. Test monthly restores.

2. Removal

  • Infection Cleanup (step-by-step)
  1. Isolate the affected machine (disconnect network cable / disable Wi-Fi).
  2. Boot into Safe Mode with Networking (Windows) or Boot an antivirus-rescue USB (Linux Environment).
  3. Update & run vendor-signed AV signature scan (many engines detect “Ransom.ALMA” variants).
  4. Examine C:\Users\Public\AppData\Roaming\README_recovery.txt or %ProgramData%\README_recovery.txt and quarantine or delete the BIN file located in the same path with identical timestamp.
  5. Clean persistence mechanisms:
    – remove registry Run key HKCU\Software\Microsoft\Windows\CurrentVersion\Run\[GUID]
    – inspect Scheduled Tasks folder for a randomly-named .bat task created around infection time.
  6. Reboot to normal mode; re-scan to confirm eradication.

3. File Decryption & Recovery

  • Recovery Feasibility: Older builds of ALMA used ECDH+ChaCha20 to wrap per-file keys and left the private master key leaked in early leak-shaming blog posts (2023-03-15), enabling full decryption.
  • Essential Tools/Patches:
    • alma-decrypt_v2.exe (en-US/US-CERT verified) – command-line utility that ingests the leaked private key.
    • Patch: Microsoft KB5009616 (Feb-23 CU) – addresses a chain-of-exploits abused post-initial access.
    • Repo: https://dev.n1nty.org/alma-decrypt (PGP-signed releases). Need at least hostname.tid and public.ecc file which ALMA deposited on the infected machine for key licensing purposes.
    Note: Victims on build ≥3.2.1 (May-23 wave) use RSA-4096+AES-256 and cannot be decrypted at time of writing; for such samples, the only viable route is backup restore.

4. Other Critical Information

  • Unique Characteristics:
    • Inserts a 48-hour timer into the ransom note and behaves nation-state-like, starting selective file shredding at expiry.
    • Disables VSS, USN journal, and Windows Defragmenter whilst leaving .lnk files untouched—reducing visual chaos but preserving discovery.
    • Collects volume serial numbers to generate deterministic “checksum” logs; researchers leverage these to correlate campaigns.
  • Broader Impact:
    • The May-2023 rerun took down 1 200+ SME NAS boxes via Log4j—first time low-intensity ransomware caused widespread data-loss directly on NAS platforms (QNAP, Synology v4.4.x).
    • Because the master key leaked, ALMA is now embedded in threat-intel feeds as an historic case study on supply-chain exploitation compounded by poor secret management.

Last reviewed 2024-05-14