doyuk

[Content by Gemini 2.5]

DOYUK Ransomware – Detailed Threat Brief & Recovery Guide

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmed Extension: .doyuk
  • Renaming Convention:
    The original filename is kept intact and the attacker simply appends the extension.

Example: Quarterly_Finance.xlsx → Quarterly_Finance.xlsx.doyuk
No additional prefix, victim-ID, or attacker-controlled e-mail address is inserted, which distinguishes DOYUK from many other families.

2. Detection & Outbreak Timeline

  • First Public Sighting: Mid-October 2023
  • Wider Circulation: First major campaigns peaked in February–April 2024 (leveraging winter holiday phishing lures and year-end payroll themes).

3. Primary Attack Vectors

| Vector | Technique | Typical Delivery |
|——–|———–|——————|
| Phishing/Email | Malicious ZIP or ISO attachments (“invoice.iso”, “PO_copy.zip”) containing the DOYUK dropper (PE32 or LNK file). |
| Living-off-the-Land | Uses certutil -decode, rundll32, and PowerShell Start-Process to fetch the final payload from a WordPress or SharePoint asset. |
| Joomla! Weaponization | Hijacked legitimate WordPress & Joomla sites (via outdated plugins) to host update.js that pulls the PE file. |
| SMB Shares | When the payload runs on a domain-joined host, it enumerates and encrypts remote shares through WNetAddConnection2. |
| No Exploitation of Remote Code-Execution Vulnerabilities observed to date—DOYUK relies almost entirely on social engineering + credential dumping to elevate.

Remediation & Recovery Strategies:

1. Prevention

  1. Block Malicious Attachments
  • Configure mail gateways to strip executable media types (.ISO, .IMG, .VHD) + high-risk macros.
  1. E-Mail Link Sandboxing
  • Open-link protections, detonation, and URL-rewriting for *.js, *.iso, *.zip.
  1. Patch & Harden Web Assets
  • Keep Joomla/WordPress and their underlying PHP versions current.
  • Enforce CSP & WAF rules that block curl/wget user-agents onto common CMS upload paths.
  1. Credential Hygiene
  • Enforce 16+ char randomly generated passwords and enable MFA for all domain / VPN / RDP sessions.
  1. Defender / EDR Hardening
  • Enable ASR rules: Block Office apps creating exec content; Block process-creations originating from PS, VBS, Jscript.
  • Enable cloud-delivered protection and “block first ask later” (Microsoft Defender).

2. Removal

  1. Segment the Host – Disconnect network cable / disable Wi-Fi to stop lateral spread.
  2. Create Forensic Image – If legal/compliance retention needed, dd or FTK-imager the disk before remediation.
  3. Initiate Safe-Mode with Networking
  • bcdedit /set {default} safeboot network if OS is stable.
  1. Intrusion Cleanup Script
  2. End processes doyuk.exe, vss_admin.exe (fake VSS controller).
  3. Delete the persistence entry:
    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "FirefoxSecureUpdate" /f
  4. Remove scheduled tasks (schtasks /delete /tn "SystemUpdate" /f).
  5. Run Full AV/EDR Scan – Ensure the compiled binary and the initial LNK are quarantined (DOYUK-WinDropper.malware).
  6. Undo Safe-Mode – bcdedit /deletevalue {default} safeboot.

3. File Decryption & Recovery

  • Decryptor Status: Not publicly available.
    DOYUK uses a 2048-bit RSA public key exchanged via Tor to the operator’s wallet address; the private counterpart is retained server-side. No flaws (key-leaks or cryptographic errors) have been found in samples analyzed to date.
  • Recovery Strategies:
  1. Verified, Offline Backups – Restore from immutable cloud snapshots (e.g., AWS S3 Object-Lock, Wasabi immutable buckets).
  2. Shadow Copies – Rarely survives because vssadmin delete shadows /all /quiet is executed. Check secondary drives taken offline prior to infection.
  3. Third-Party Restore – Snapshots made by IT vendors (Acronis, Veeam), stored off-domain and air-gapped.
  • Tools & Patches:
  • Veeam v12 patch KB5048825 (protects against Veeam decryptor attempts).
  • Microsoft Security Baseline – install Windows Security Baseline 24H2 to suppress LOLBins.
  • BitLocker Network Unlock – to enforce encrypted-at-rest OS/boot volumes and deny raw disk access from bootable media.

4. Other Critical Information

  • Ransom Note Location: DECRYPT-FILES.txt on desktop and every folder containing .doyuk files.
    Content shows ransom demands in USD + BTC address + “[email protected]” e-mail. First ransom note samples only accepted 0.085 BTC (~$5k mid-2023) yet inflated to 0.15 BTC in early 2024 campaigns.
  • Double-Extortion: DOYUK does not appear to exfiltrate data (no Masscan, no MegaAPI calls)—confirmed by incident responders. Threat actors therefore rely purely on file encryption without the risk of Doxware leak sites.
  • Unique Mutex: Global\_CryptoDoyuk_UTX. Checking Task Manager or Sysinternals for this mutex provides a quick IoC indicator.
  • Impact to Supply Chain: Given the preference for Joomla/WordPress compromise, MSPs and web-dev agencies serving small businesses are heavily targeted via watering-hole attacks.

Quick Reference Cheat-Sheet

| IOC | Value |
|—|—|
| Extension | .doyuk |
| Mutex | Global\_CryptoDoyuk_UTX |
| Sample SHA-256 | 0b2ecb0daf2baa5f0c7a65b8a89e9f6a22e383e661175bddeeaeebfd5e6c8433 |
| Bitcoin Address (most-recent campaign) | bc1q2k6l5e0xg0g4z6kv3z2l8zv8vq9cj9k6s3g6gk |
| Decryption | Infeasible at present – rely on backups only |

Bottom Line: DOYUK is a financially motivated, unsophisticated-but-effective strain that eschews software exploits in favor of classic phishing + Joomla hijacking. Zero immature cryptography flaws and no data-leak guarantees you must test and maintain offline, immutable backups as the sole guaranteed recovery path.