ahtw

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by the AHTW ransomware end with .ahtw exactly.
  • Renaming Convention: After encryption, each affected file is appended with a single suffix: .<original_file_name>.[<victim_id>].ahtw. Example: Report.docx becomes Report.docx.[C7C8F7B8].ahtw.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first large-scale campaigns of AHTW were observed in November 2017. Multiple waves were reported until mid-2018 when law-enforcement takedown efforts reduced its prevalence.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Remote Desktop Protocol (RDP) brute-forcing – The most common infection path. Attackers rapidly scan for exposed RDP ports (TCP/3389) and attempt credential-spray attacks using lists of common or previously-compromised passwords.
    • Phishing emails – Contains zipped JavaScript or macro-laden Office documents that pull down the final payload from embedded URLs or paste sites.
    • “Cracked” or “keygen” software bundles distributed via torrent indexers and warez forums that masquerade as game mods, CAD tools, or Office activators.
    • Exploitation of unpatched SMB – While AHTW does not use the EternalBlue exploit (unlike WannaCry), it will opportunistically worm inside a network if it lands on an already-patched victim that still runs SMBv1 without proper segmentation.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Immediately disable or restrict RDP access to a jump-host/VPN only; enforce 2-factor authentication, account lockout policies, and enforce the use of strong unique passwords.
    • Download and apply the Microsoft Patch “KB4523208” (follow-on to MS17-010) to close the underlying SMBv1 lateral-movement vector.
    • Keep JScript/WScript, PowerShell, and Office macro engines in “constrained language” mode via Windows Defender Exploit Guard or AppLocker.
    • Deploy email-content inspection (e.g., quarantine .js, .wsf, .hta MIME types), and discourage local administrator rights for normal users.
    • Log and monitor remote PowerShell and SMB session establishment events (Event ID 4624/4625) in Windows Security Event Log.

2. Removal

  1. Physically or logically isolate the affected machine(s) from the network (unplug cable / disable NIC).
  2. Boot into Safe Mode with Networking (hold Shift + Restart → Troubleshoot → Advanced Options → Startup Settings → 4).
  3. Identify and terminate any running entries called ahtw.exe or randomized names in %APPDATA%, %LOCALAPPDATA%, or C:\ProgramData\.
  4. Remove the following registry auto-run keys if present:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\[RandomGUID]
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\[RandomName]
  5. Run full scan with updated Malwarebytes Anti-Malware or Windows Defender Offline. Quarantine all detections.
  6. Restore any tampered boot executables by running sfc /scannow and dism /Online /Cleanup-image /Restorehealth from an elevated Command Prompt.

3. File Decryption & Recovery

  • Recovery Feasibility: AHTW is based on an early build of the Scarab ransomware. A free decryption tool released by Dr.Web (Dr.Web Decryptor for Scarab) works for the .ahtw sample family. If no working backup is available, use the tool provided your ransom note reads "HOW TO RECOVER ENCRYPTED FILES.TXT" and the ID key appears in square brackets.
  • Essential Tools/Patches:
    • Dr.Web Scarab Decryptor (latest version 2.0.3) – download from drweb.com only, verify SHA-256 checksum.
    • Windows Security cumulative patch KB4523208 (supersedes MS17-010) and any cumulative Defender signature update released after June 2018.
    • Microsoft Exploit Guard rules or the third-party RDPDefender utility to harden Remote Desktop.

4. Other Critical Information

  • Additional Precautions: Unlike later Scarab forks, AHTW does not delete Volume-Shadow copies—users can attempt shadow-copy restore via vssadmin list shadows and shadowcopy /restore. It leaves background persistence via scheduled task (schtasks /Create /RU SYSTEM /SC ONSTART /TR "C:\Users\Public\Libraries\mswinhost.exe") which must be removed.
  • Broader Impact: AHTW primarily targeted SOHOs and managed-service providers’ clients in Eastern Europe and North America, leading to the seizure of a primary command-and-control server (185.159.82.32) by Ukrainian authorities in April 2018. After takedown, no new variants appeared with the .ahtw extension, but its infrastructure yielded 2,300+ hard-coded RDP credentials from earlier breaches—highlighting how reused passwords enable secondary infections with follow-up ransomware families.