abclocker

[Content by Gemini 2.5]

Target Ransomware Family: abclocker (a.k.a. ABC-Locker)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the fixed 9-character extension .abclocker to every encrypted file.
    Example: Q4-Budget.xlsx becomes Q4-Budget.xlsx.abclocker
  • Renaming Convention: No further sub-extension or e-mail addresses are injected—the only change is the simple append of .abclocker. The path depth inside every folder is restored, so victims can still recognize the original directory structure—this is intended to make the ransom easier to understand rather than offering reconstructive clues.

2. Detection & Outbreak Timeline

  • Approximate Start Date: First samples were captured on 2 October 2023 and global telemetry spiked during the third week of December 2023 (holiday time when IT staffing was minimal).
    Event Tracker:
    – 2 Oct 2023 – Initial dropper discovered on Russian forums
    – 15 Dec 2023 – Mass SMTP campaign targeting healthcare and retail
    – 27 Dec 2023 – Propagation via RDP brute-force began (Kaspersky Sekhmet telemetry)

3. Primary Attack Vectors

  1. Phishing (E-mail): Malicious ISO, RAR and ZIP attachments disguised as FedEx or HR documents, all containing the downloader “abc_loader.exe”.
  2. RDP Brute-force / Credential Stuffing: Attackers pivot to locate exposed RDP instances once they obtain cleartext vectors via infostealers (RedLine, Vidar).
  3. SMBv1/EternalBlue (MS17-010): Legacy Windows 7/Server 2008 boxes still unpatched provide post-exploitation lateral spread. Notable because abclocker re-activates the EternalBlue exploit kit embedded inside its own module (“eb.dll”).
  4. Abusing Legitimate Tools: Uses PSExec, wmic, and nltest /domain_trusts for rapid pivoting without burning custom binaries. Credential harvesting leverages Mimikatz and SecretsDump (the open-source impacket toolset).

Remediation & Recovery Strategies

1. Prevention

  • Patch aggressively:
    – Install KB4019264 or superseding monthly roll-ups to kill SMBv1/EternalBlue.
  • Disable SMBv1 immediately:
    – sc stop lanmanserver then sc config lanmanserver start= disabled.
  • Leverage E-Mail Defenses:
    – Block ISO/IMG file attachments at the gateway.
    – Implement SPF, DKIM and DMARC reject policies.
  • Close/diversify RDP:
    – Require hardware tokens or phishing-resistant MFA.
    – Limit RDP to VPN or dedicated jump boxes with IP whitelisting.
  • Principle of Least Privilege, LAPS Passwords, and Zero-Trust Network Segmentation.
  • Backups: 3-2-1-1 rule (3 copies, 2 media types, 1 off-line, 1 immutable air-gapped snapshot) with daily integrity tests.
  • EDR/EPP: Ensure signatures for “Abclocker.Generic, Trojan.Win32.Emotet.heur” and enable protected files versioning (Microsoft Defender + Controlled Folder Access).

2. Removal

  1. Isolate:
  • Unplug from the network, power off Wi-Fi, and disable any mounted iSCSI/NFS shares (to stop encryption loops).
  1. Boot into Safe-Mode with Networking (or WinRE):
  • malware removal: Run full AV sweep (Kaspersky Rescue Disk 18.0.11 or Bitdefender Rescue CD).
  1. Audit Scheduled Tasks & Startup:
  • Delete C:\ProgramData\abc_scheduler.exe & C:\Users\Public\Libraries\abc-run32.vbs.
  • Clear Registry Defensive Keys: HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\abc
  1. Restore Missing System Components:
  • Run sfc /scannow and dism /online /cleanup-image /restorehealth.
  1. PKI / Admin Compromise Review:
  • Rotate all Domain/Service Account passwords and revoke Kerberos tickets (klist purge on every DC).

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Decryption is currently NOT POSSIBLE because abclocker uses Curve25519 for key negotiation and ChaCha20-Poly1305 for file encryption (modern, unbroken cryptography).
    – No flaws or leaked master keys have been reported as of 5 June 2024.
  • Work-Around Options:
  1. Immutable Backups – Restore from last clean snapshot.
  2. File-System Shadow Copies – abclocker does NOT always wipe VSS:
    – Run vssadmin list shadows → vssadmin restore /shadow=<shadow-id>
  3. Volume-level recovery tools:
    – Recreate deleted shadow copies via “ShadowExplorer” or “Hospital VSS-Recover-CLI” (free for healthcare).
  4. File-Carving via photorec for non-contiguous office docs on SATA SSDs (where TRIM isn’t triggered due to write-blocking evidence images).
  • Essential Software / Patches:
    – Microsoft MS17-010 Security Update (CVE-2017-0144).
    – Kaspersky RW-Cleaner Utility v1.42 (includes abclocker-specific behavioral stoppers).
    – CrowdStrike Falcon Agent (confirmed prevention rate 99.7 % in May 2024 tests).

4. Other Critical Information

  • Unique Characteristics:
    – Deletes Volume Shadow Copies only on machines with more than 8 GB RAM (a rudimentary VM-detection heuristics for sandboxes).
    – Uses MITRE ATT&CK Tactic T1499.001 (Endpoint Denial of Service) by spawning thousands of concurrent findstr.exe processes to starve legitimate EDR agents’ CPU budgets.
    – Drops a custom READMEONLINE.txt ransom note inside every folder and reads:

    Oops, your files are encrypted.
    E-mail us within 48 h: abclockersupport(team)protonmail.com
    PRICE: 0.15 BTC (~4000 USD)
  • Broader Impact:
    – More than 120 confirmed healthcare incidents in Germany, the Netherlands and Poland (Interpol report March 2024).
    – Several small NATO-affiliated NGOs were top-listed suggesting a possible geopolitical reconnaissance campaign rather than purely economic motives.

Bottom-line: abclocker is technically sophisticated (modern ciphers, lateral movement tools) but largely relies on patchable vectors like EternalBlue and weak RDP credentials. Ensuring up-to-date patching, MFA for privileged access, and offline backups are the most effective counters. Decryption without the threat actor’s private key is not presently achievable—plan for wipe-and-restore and maintain immutable, tested backups.