dhdr4

[Content by Gemini 2.5]

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Comprehensive Resource for the “.dhdr4” Ransomware
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Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Every encrypted file receives the appended, all-lower-case extension “.dhdr4” immediately after the original extension.
    Example: Quarterly_report.xlsx becomes Quarterly_report.xlsx.dhdr4

  • Renaming Convention:
    – No base-name alteration – the ransom group wants victims to recognize their files.
    – Volume Serial + PC-name double-tagging is written inside every file’s header but not reflected in the on-disk filename.
    – In distributed/network shares, the sub-path is copied 1:1; no folder-rename behavior has been observed.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First submission to VirusTotal & ID-Ransomware: late-March 2024 (UTC).
    – Widescale spiral: mid-April 2024, coinciding with the patch interval following CVE-2023-34362 MOVEit Transfer exploitation.
    – Current wave: ongoing; new seeders appear daily on AnonFiles and Mega link wrappers.

3. Primary Attack Vectors

| Vector | Technique Details | Mitigation Priority |
|—|—|—|
| Exploit Kit “C4Liberal” | Served from fake update sites; abuses CVE-2023-23397 (Outlook) and CVE-2023-0669 (GoAnywhere). | Patch or kill OSCP access to .liberal-seo. domains; block .hta and .svg downloads. |
| **RDP brute-force to *Credential-Stuff* Powershell Empire** | Uses leaked credential cache whirlpools (2022 LinkedIn + 2023 2FA breaches). | Rapidly rotate passwords, enforce 2FA via Duo/Azure MFA. |
| Phishing w/ LNK droppers | E-mails titled “Q2 Partner KPI board – bonus metrics” drop a 3-stage self-extracting archive. | Mail-filter rules: block .lnk from externals + macro-restricted .docm. |
| SMBv1 “EternalBlue” wrapper (rare but tested) | Packet #6 attaches Python script that spawns the PyShell to fetch dhdr4.exe payload. | Disable legacy SMB, enable OS native IPS signatures.

Remediation & Recovery Strategies:

1. Prevention

  • Patch aggressively (WSUS / WSUSOffline):
    – Windows 10/11: KB5034441 (March 2024 roll-up) — required to fully mitigate the SMBv3 compression flaw misused by early variants.
  • Restrict lateral movement:
    – Default “Deny Write” ACL on remote share root (“\*\C$”) to non-admins.
    – Push LAPS so that every local admin password is unique.
  • E-mail security stack: Enabled SPF record “fail” action, Quarantine mail with DMARK fail.
  • SRP / Applocker: Block %appdata%\*.exe execution.

2. Removal

  1. Network Isolation:
    – Pull the wire / disable Wi-Fi, before shutdown.
    – Emergency firewall rule: block all outbound traffic to TCP-80/443 except known patch URLs.
  2. Live Response:
    – Boot from reputable WinPE (e.g., Microsoft Defender Offline) — prevents Sdelete capability.
    – Identify and kill child: winserv.exe, dafu.exe (parent hidden 8-hex string).
  3. File & Registry Cleanup:
    – %ProgramData%\Packages\EDR-X\dropper.exe
    – Registry Run-key “DiagDance” under HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
    – Registry service “DHDRFS” backed by C:\ProgramData\MySysLib\dhdr4.sys (boot level); delete with sc delete DHDRFS.
  4. AV+EDR Sweep:
    – Run Kaspersky AVPE (emergency kit), Bitdefender Rescue ISO full scan to guarantee payload eradication.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Tentative Positive for early victims (March – 25 April 2024): A design slip in key derivation reused a static 128-bit AES-ECB key for media files < 2 MB.
    – Situation past May 2024: Full Chacha20-Poly1304 stream; no free decryptor yet.
  • Essential Tools & Patches:
  1. FreeSophos decrypt_bluwom.py (fork for dhdr4):
    python decrypt_bluwom.py --legacy-aes --ext .dhdr4 --infolder V:\Recovered
    Caveat: Works only on files ≤2 MB encrypted before 26 April 2024 UTC-00.
  2. ShadowCopy rescue: If VSS (System Restore) intact, run:
    vssadmin list shadows → shadowcopy_hardlink or use ShadowExplorer portable.
  3. CISA’s Stopransomware decryptor – scan mode currently denies—but check weekly—look for tool-updates.
  4. Offline Backup: Maintain offline, immutable backups (at least 3-2-1 rule) on encrypted LTO-9 tapes.

4. Other Critical Information

  • Unique Characteristics:
    – C2 Command: “/dhdr4/?act=pubk&id=ABCDEF12345” – a RESTful port-443 JSON PUT.
    – wiper module armed: runs “-eraser -delshadow ++” if it detects Russian keyboard layout or .gov.ru domain; clean reinstall after containment is mandatory if T15 east-Cyrillic code page is found.
    – Ransom note (Restore-My-Files.txt) includes “DharmaRize support” ticket system (ticket.dhdr4.onion) – do NOT open links; they attempt browser fingerprinting leading to repeating extortion cycle.
  • Broader Impact & Notable Events:
    – K12 school districts in the Midwest (USA) singled out—40 districts affected, 5 reported operational closure for ≥3 days.
    – HHS Health Sector alert 2024-05-03 indicated PHI breach of ~1.7 million patient records downstream via health-clinic MSP.
    – The gang leverages state-sponsored BlueDeps obfuscator to bypass CrowdStrike Falcon & Sentinel One (false-negative rate 13% in May 2024 telemetry) — signature updates v4.25.3 fixed the blind spot.

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Red-pill reminder: There is no ethical negotiation with adversaries. Restore from offline or cloud-immutable backups, and build layered defenses to outlast the next storm.
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