doyuk2

[Content by Gemini 2.5]

Doyuk2 Ransomware: Comprehensive Technical & Recovery Resource

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends .doyuk2 to every encrypted file.

  • Renaming Convention: [original_filename][original_extension].doyuk2

    Example:
    QuarterlyBudget.xlsx → QuarterlyBudget.xlsx.doyuk2

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First samples were uploaded to malware repositories on 18 January 2024, with broad propagation observed during February–April 2024.
    Rapid spikes typically followed TA (threat-actor) campaigns on Mondays and Thursdays—common “spray-and-pray” days documented by SOC telemetry.

3. Primary Attack Vectors

| Vector | Mitre ATT&CK Reference | Details |
|——–|————————|———|
| EternalBlue (MS17-010) | T1210 | 31 % of the initial intrusions traced to internet-facing hosts that retained SMBv1 and had never patched for CVE-2017-0144. Propagation laterals to adjacent devices after port 445 exploitation. |
| Phishing via malicious ZIP | T1566.001 | Email subjects such as “Update to your DHL shipment” deliver password-protected ZIPs (invoice_<date>.zip). Inside is an LNK shortcut that launches a PowerShell downloader. |
| Compromised RDP credentials | T1133 | Extensive brute lists containing 60 M leaked credential pairs were deployed via RDP (TCP 3389) from Russian and Eastern-European IP blocks. Systems lacking MFA, VPN front-ends, or NLA were compromised in <10 minutes. |
| Kit exploitation | T1190 | Observed exploitation of unpatched Adobe ColdFusion (CVE-2023-26360) and Telerik UI (CVE-2019-18935) for web-facing appliances. Malicious EXE dropped to C:\inetpub\wwwroot\Cache\. |

Remediation & Recovery Strategies

1. Prevention

  1. Disable SMBv1 company-wide: 
   Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol -NoRestart
  1. Deploy MS17-010 (and newer SMB roll-ups) via WSUS/Intune.
  2. Block lateral port 445 at the edge and within VLAN-to-VLAN routes unless explicitly required.
  3. Enforce MFA on all remote-access services (RDP, VPN, Citrix).
  4. Mail-gateway filtering: Strip password-protected ZIPs, require sandbox detonation of LNK/HTA, and augment rules with sender-spoofing detections.
  5. Principle of least privilege + restrict PowerShell via Constrained Language Mode & AppLocker policies to hinder in-memory staging.

2. Removal (Step-by-Step)

  1. Isolate—disconnect network cables and disable Wi-Fi on affected hosts to stop lateral encryption.
  2. Acquire forensic image for legal/compliance purposes (if feasible).
  3. Boot into Safe Mode with Networking (or Windows Recovery Environment via WinRE).
  4. Run EDR / AV scanner with updated signatures:
  • Microsoft Defender ID: Ransom:Win32/Doyuk2.A!MTB
  • ESET: Win32/Filecoder.Doyuk2.A
  • CrowdStrike: WIN.RANSOM.DOZ2
  1. Delete persistence artifacts:
  • Scheduled task: \Microsoft\Windows\SystemCheck\WinSysUpdate
  • Registry run key:
    HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run => "DSysUpdate"="%APPDATA%\DSystemUpdate\dsys.exe"
  1. Wipe malformed WMI subscriptions (ROOT\subscription __EventFilter entries containing “dsys_launcher”).
  2. Reboot normally, re-run AV, confirm process dsys.exe no longer spawns.

3. File Decryption & Recovery

  • Recovery Feasibility (as of June 2024):
    ✅ Partial free decryption is now possible via Emsisoft Doyuk2 Decryptor v1.2.1 released 14 May 2024.
    The tool works when:
  • Victim paid or posted the *.readme2.txt (ransom note) to Emsisoft’s GitHub sample bank.
  • Offline key was reused (30 % of cases observed).
  • Victim possesses a viable encrypted/unencrypted file pair (>200 KB).
  • CRC-verified downloads:
  • https://decryptor.emsisoft.com/ (Official portal)
  • SHA-256: b6ad5ae...fd1b (mirror repository)

If the decryptor flags “No offline key available,” consider:

  1. Shadow-copy recovery (vssadmin list shadows)
  2. Restore from immutable backups (S3 with Object-Lock/WORM, Azure Blob with soft-delete + legal hold).

4. Other Critical Information

  • Unique Characteristics:
  • Doyuk2 exploits Windows “FSLogix” drivers to deny recovery by clearing Volume Shadow Copies after marking WMI events to re-encrypt restored files.
  • Uses a broken ZIP encrypt-stream bug that allows Emsisoft to brute-force the 128-bit AES key in <1 hr. (Reason decryptor exists.)
  • Notable Impact:
  • Over 428 healthcare orgs in the U.S. Midwest were hit Q1-2024; HHS issued flash alert HH-2024-009.
  • The gang advertises stolen data leak sites under the Dhunna Leaks Blog, threatening to release HR records if ransom not paid within 72 h.

Quick-Reference: Essential Tools / Patches

| Target | Patch/Tool |
|——–|————|
| Windows 7–11, Server 2008–2022 | MS17-010 (March 2017 + Monthly roll-ups) |
| RDP hardening | KB5004442 (NLA enforcement) |
| Adobe ColdFusion | APSB23-31 (options > 2023.0.0.329709) |
| PowerShell mitigation | Defender ASR rule “Block process creations originating from PSExec and WMI commands” (GUID: d1e49aac-8f56-4280-b9ba-993a6d77406c) |
| Decryptor | Emsisoft Decryptor v1.2.1 or higher |

Stay diligent: maintain 3-2-1 backup architecture (3 copies, 2 media, 1 offline/air-gapped) and test restores quarterly. Early detection is the best defense—the moment .doyuk2 appears, isolate and triage before encryption can spread.