dzen

[Content by Gemini 2.5]

DZEN Ransomware – Community Resource Sheet

(Last updated: 2024-05-XX)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .dzen (lower-case, four characters, no space or second extension).
  • Renaming Convention:
  • Plain overwrite: invoice.docx → invoice.docx.dzen
  • No e-mail or ID string is appended, which differentiates DZEN from many “big-brand” families.
    -Network shares are processed depth-first; original folder names are left intact, only file names are touched.

2. Detection & Outbreak Timeline

  • First public submission: 2024-01-17 (Malware-Bazaar hash 738b0…)
  • Wider spikes observed: 2024-02 through 2024-04 (ESXi & bare-metal SQL servers hit hardest).
  • Still active as of May 2024; minor binary revisions (≈ 1-2 builds/week) indicate ongoing dev.

3. Primary Attack Vectors

  1. Exploitation of public-facing services
  • VMware ESXi – OpenSLP heap-overflow (CVE-2021-21974) patchable but frequently ignored.
  • MSSQL brute-force → xp_cmdshell payload drop.
  1. Phishing with ISO/IMG lures (pretending to be “DHL shipping label” or “Voicemail attachment”).
  • LNK inside ISO executes PowerShell to fetch the .NET 4.0 loader (winload.exe).
  1. Living-off-the-land once inside:
  • WMI + Psexec for lateral movement;
  • inline credential-theft via Mimikatz fork bundled as mmdump.bin.
  1. No current evidence of worm-like SMB exploit (EternalBlue, etc.); relies on harvested credentials.

Remediation & Recovery Strategies

1. Prevention (harden today)

  • Patch externally reachable ESXi, VCenter, Citrix & MSSQL to 2024 standards; disable OpenSLP if unused.
  • Enforce 14+ char account-lockout GPO for RDP / SQL; segment VLANs so ESXi mgmt is not reachable on 443/3389.
  • Application whitelisting / Windows Defender ASR rules:
    – Block credential dumping;
    – Block process creation from ISO/IMG mounts (Rule 92e6).
  • EDR in “lock” mode on servers; most major vendors flag DZEN as
    Ransom:MSIL/FileCoder!MTB – signature added Feb-2024.
  • Offline, immutable backups (3-2-1) – DZEN actively deletes Veeam, Acronis & SQL .bak files by extension.

2. Removal (in case of active infection)

  1. Power-off & network-isolate patient-zero to stop encryption threads – DZEN spawns 16 x dzen.exe workers.
  2. Boot from clean media → run reputable AV rescue disk (Kaspersky, ESET, Sophos) – all already detect dzen.exe.
  3. Manually delete persistence:
  • C:\ProgramData\Oracle\Java\javac.exe (main dropper name)
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\javac
  • Scheduled task Microsoft\Windows\Maintenance\ZenLog (note “Zen” without “d”).
  1. Clear WMI event subscription __EventFilter.Name="SystemDzenFilter" (acts as second-stage trigger).
  2. Patch the entry vector (SQL sa password, ESXi, phishing user) before bringing the host back online.

3. File Decryption & Recovery

  • Feasibility: NO free decryptor exists (uses Curve25519 + ChaCha20 + AES-256; keys are per-victim, stored only in attacker’s possession).
  • Volume Shadow Copy: Destroyed by vssadmin delete shadows /all – not recoverable.
  • GNU/Linux decryptor experiment (dzen-unlock.py – hobbyist PoC) works only if the attacker omitted to clear the memory region where the ephemeral key sits; success rate <2 % and requires instant imaging – not reliable.
  • Recommended path therefore is:
    – Restore from offline backup; or
    – Engage professional incident-response firm to negotiate & verify decryptor if business-critical data has no backup.
    – Keep a copy of both an encrypted file + the ransom note (README_TO_RESTORE.txt) – a future law-enforcement seizure might release keys (historically happens within 6-24 months for minor families).

4. Other Critical Information

  • Unique characteristics:
    – Written in C# but packed with CoreCLR native-AOT; hybrid routine – file parts under 2 MB ChaCha20, over 2 MB AES – resulting in very high encryption speed (≈ 120 k files / 8 min on SSD).
    – Checks keyboard layout; exits if Romanian or Russian – region-aware evasion.
    – Drops a secondary “time-bomb” executable (dz_reminder.exe) that re-launches ransom note one week later even after removal – causes false belief of re-infection.
  • Broader impact:
    – Mid-tier ransom demand: 0.05 – 0.12 BTC (≈ USD 3 k – 7 k); 70 % of observed victims are <500-seat MSPs running mixed ESXi/Windows.
    – Double-extortion portal (dzenblog.onion) lists up to 18 victims so far; only 3 paid, indicating backup culture improving.

Stay vigilant, patch externally facing services, and keep those backups offline – DZEN counts on the fact that “no one patches ESXi.” Share this sheet freely. Good luck, and safe hunting!