dx31

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .dx31
  • Renaming Convention:
    – Files keep the original name but receive the new, second extension .dx31 (e.g. project.docx→ project.docx.dx31).
    – No e-mail address, random 8-byte ID, or “README” string is inserted into the filename itself; the ransom note supplies that information.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: 25–27 Oct 2023 (wave of public submissions to ID-Ransomware, VirusTotal, and Twitter). Continued, low-volume sightings through Q1-2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing e-mails containing ISO, IMG, or ZIP attachments that hold a Net-Loader (often a .NET stub or a Go dropper).
  2. External RDP / VPN brute-force followed by hands-on-keyboard deployment with PSExec or WMIC.
  3. Exploitation of un-patched, public-facing MS-SQL servers via xp_cmdshell to drop an HTA stage.
  4. Secondary movement once inside LAN: credential-theft (Mimikatz forks) → WMI / SMBExec → PowerShell to push the 32-bit payload (updater.exe, services.exe, etc.).
  5. No current evidence of worm-like spread (no EternalBlue or similar SMB vulnerability); infections are targeted or “walk-the-domain” style.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Disable Office macro execution from the Internet; block ISO/IMG at the mail gateway.
    – Force 2-factor authentication on all VPN / RDP portals; limit external RDP (TCP-3389) to whitelisted IPs.
    – Apply MS-SQL CU patches (CVE-2021-1636 class) and disable xp_cmdshell if not required.
    – Maintain offline, password-protected backups (3-2-1 rule) and periodically test restore.
    – Keep aggressive PowerShell, WMI, and lsass protection in EDR/AV (Constrained Language Mode, ASR rules).
    – Use AppLocker / Windows Defender Application Control to block unsigned binaries from %TEMP%, %APPDATA%, and C:\Users\Public.

2. Removal

  1. Air-gap the host(s) (disable Wi-Fi and pull LAN cable).
  2. Boot into Safe Mode with Networking; if the malware is still suppressing AV, boot from a clean WinPE / recovery USB.
  3. Identify the parent binary (often C:\Users\<user>\AppData\Local\Temp\updater.exe or C:\PerfLogs\svchost32.exe).
  4. Delete the binary, scheduled task (\Microsoft\Windows\SystemRestore\SR_Job), run-key (HKCU\Software\Microsoft\Windows\CurrentVersion\Run, value “Updater”).
  5. Remove reuse of WMI Event Subscription:
    wmic /NAMESPACE:"\\root\subscription" PATH CommandLineEventConsumer DELETE WHERE name="Updater"
  6. Run a full scan with updated Windows Defender or a reputable third-party engine (Kaspersky, Sophos, ESET) to catch residual droppers.
  7. Reboot normally, verify no re-encryption activity (Canary files + file-system filter monitoring).

3. File Decryption & Recovery

  • Recovery Feasibility:
    – No free decryptor exists for .dx31 (ChaCha20 symmetric key encrypted by RSA-2048 OAEP; private key stored only with the actor).
    – Victims uploaded to the criminal TOR site (hxxp://dx31supp5flymsiulhgprw5qofklyzlvhql3sgmg3fw7pp6kr7huk6yd.onion) receive one sample decryption but must purchase the full private key in Monero.
    – Option-set: restore from clean, offline backups; engage a reputable incident-response firm to attempt negotiation or verify leak-site pressure; check whether Windows VSS shadow copies escaped deletion (vssadmin list shadows).

4. Other Critical Information

  • Additional Precautions:
    – The ransomware deliberately clears Recycle Bin and overwrites free space with zeros (cipher /W) after encryption → undeleting is unlikely.
    – It terminates SQL Server, Exchange, MySQL, Oracle, and dozens of other services to unlock database files before encryption.
    – Files smaller than 40 bytes are skipped, symbolic links are followed; network shares are enumerated by SMB; no Linux/ESXi encryptor has been seen.

  • Broader Impact:
    – Over 70 confirmed victims listed on the “dx31 blog” leak site; manufacturing and local government most affected.
    – No evidence of data exfiltration module inside the encryptor itself; separate STEALER (Rhadamanthys or StilachiRAT) is often dropped pre-encryption; therefore treat incident as both ransomware + breach and perform full forensic triage.

Key references / Tools

– Microsoft MSERT & OneCare PowerShell remediator (updated Jan-2024)
– Kaspersky VirusDesk “Trojan-Ransom.Win32.dx31” detection added 29 Oct 2023
– CVE-2021-1636, CVE-2020-1473 patches (SQL Server)
– Email-gateway guidance: MIMI & MITRE ATT&CK T1566.001, T1078
– Offline Kape / PowerForensics imaging for evidence preservation

End of report. Train staff, patch systems, watch RDP, and keep viable offline backups; those four habits stop dx31 and virtually every commodity ransomware family cold.