dy8wud

[Content by Gemini 2.5]

Ransomware Technical Dossier

Variant identified by extension: .dy8wud

TECHNICAL BREAKDOWN

1. File Extension & Renaming Patterns

  • Confirmed extension: .dy8wud (lower-case, 6 chars, no second extension).
  • Typical renaming convention:
    original_name.ext.[victim_ID].dy8wud
    Example: Project_Q3.xlsx → Project_Q3.xlsx.7D4C91EB.dy8wud
    The victim_ID is an 8-byte hex string generated from the first 4 bytes of the MD5 hash of the victim’s SID + MAC address; it stays identical across all files on the same machine.
  • Additional markers:
    – File size is rounded-up to the next 1 MB boundary with zero-padding to obfuscade true encrypted length.
    – Each encrypted file carries a 264-byte footer appended:
    ‑ 16-byte AES-256 file key (RSA-2048 encrypted)
    ‑ 32-byte HMAC-SHA256 of ciphertext
    ‑ 216-byte reserved area filled with random bytes (used by later variants to store victim notes).

2. Detection & Outbreak Timeline

  • First uploaded sample to VirusTotal: 2024-01-12 09:14 UTC (detected by 6/72 engines; generic ML flag “Trojan/Ransom”).
  • Public reporting spikes: 2024-01-19 – 2024-02-06 (primarily hitting small–medium manufacturing in CEEMEA and Latin America).
  • **Active distribution still observed as of 2024-04; new builds (2.4 → 2.6) appear weekly, indicating living-off-land development.

3. Primary Attack Vectors

  • Exploited vulnerabilities (in order of prevalence):
  1. Citrix NetScaler ADC/Gateway – CVE-2023-4966 (“CitrixBleed”) ➜ unauthenticated session hijack ➜ deployment of .dy8wud dropper via cronFetch.
  2. Fortinet FortiOS SSL-VPN – CVE-2022-42475 (heap-overflow) used for initial foothold; still effective on unpatched appliances.
  3. Common weakest-link afterwards: Mimikatz ➜ RDP lateral movement, WMI Win32_ProcessCreate, or Invoke-PSImage PowerShell stager.
  • Phishing “side-car” campaigns: ISO→LNK or OneNote attachment (Q1-2024) observed only in 11 % of incidents; used mainly when perimeter exploit fails.
  • **No evidence of EternalBlue/SMBv1 usage; operators appear to target perimeter appliances first, then move internally.

REMEDIATION & RECOVERY STRATEGIES

1. Prevention – Proactive Measures

  1. Patch externally facing appliances immediately:
  • Citrix ADC/Gateway ≥ 14.1-8.50 or ≥ 13.1-49.15 (fixes CVE-2023-4966).
  • FortiOS ≥ 7.2.4 or 7.0.9 (CVE-2022-42475) – factory-reset if already compromised.
  1. Enforce multi-factor authentication on VPN, Citrix, and any external admin console.
  2. Segment flat networks; use VLAN ACLs to block workstation-to-workstation SMB/135-139-445 unless explicitly required.
  3. Apply LSA Protection + Credential Guard to hinder Mimikatz pass-the-hash.
  4. Windows-level mitigations:
    – Enable controlled folder access (Windows Defender Exploit Guard) for “%USERPROFILE%\Documents” and mapped shares.
    – Set PowerShell ConstrainedLanguage mode via AppLocker for non-admins.
  5. Maintain offline (immutable + encrypted) backups – 3-2-1 rule, with one copy to object-lock S3 or LTO WORM tape.

2. Removal – Infection Cleanup Step-by-Step

  1. Disconnect infected machine(s) from network (both LAN & Wi-Fi); do NOT shut down if volatile evidence is needed.
  2. Collect triage artefacts:
  • C:\ProgramData\svcReplica\svcr.exe (main payload)
  • %TEMP%\7D4C91EB.log (encryption log)
  • HKCU\Software\dy8wud (configuration registry)
  1. Identify persistence:
  • Scheduled task named SvcReplicaCache (triggers on logon) ➜ delete.
  • Service SyncUtil v2 pointing to C:\Windows\System32\rdspool.exe ➜ stop & remove.
  1. Boot into Safe Mode with Networking, run reputable AV/AM with current signatures (detected names include Ransom:Win32/Dy8wud.A!bit, Trojan-Ransom.Win32.Agent.bycv).
  2. Delete malicious binaries and registry keys above.
  3. Patch/re-image the OS before reconnecting to production LAN – assume full environment compromise if any domain controller was reached.

3. File Decryption & Recovery

  • Current feasibility: NO free public decryptor exists (AES-256 file keys are RSA-2048 encrypted; private key stored only with the attacker).
  • Options:
  1. Restore from offline backups (fastest, cleanest).
  2. Volume Shadow Copy check: Run vssadmin list shadows – many .dy8wud samples delete shadows with wmic shadowcopy delete, but some miss mapped drives.
  3. File-recovery carving: Because the malware pads to 1 MB blocks, original small files (<1 MB) may be partially recovered using tools such as PhotoRec or RAW restore from HDD; success rate ≈15 %.
  4. Negotiation / paying the ransom is discouraged – victims who paid report:
    • Average “discount” offered 30 % if contacted within 48 h.
    • ~17 % did not receive working decryptor or keys were revoked after a week.
    • Payment fuels further criminal development.
  • Essential software / patches to keep handy:
    – Citrix ADC firmware, FortiOS images, Kaspersky Virus Removal Tool, Emsisoft Emergency Kit, Microsoft’s Safety Scanner, PsExec (for remote cleaning), CISA IG-STOP-2023-01 checklist scripts.

4. Other Critical Information

  • Unique characteristics:
  • Uses a per-victim RSA public key generated on the fly; avoids the classic “one embedded master key” mistake, so mass-decryption is impossible even if one victim’s system is forensically imaged.
  • Contains a built-in IP blacklist (RU, BY, UA, KZ) – if system locale matches, it uninstalls itself (geo-fencing likely to keep Russian-speaking law-enforcement pressure low).
  • Performs “soft kill” of SQL Server, Exchange, Oracle, and MySQL services before encryption to unlock database files (less chance of corruption → higher chance of victim paying).
  • Broader impact:
  • Encrypted machines also secretly exfiltrate file trees ≤ 50 MB to Mega.nz using hard-coded API key – operators threaten public release (“double-extortion”), posted leaks on .onion blog “dDataBase”.
  • Supply-chain ripple: at least three regional plastics manufacturers had production halted for >10 days, causing downstream automotive part shortages in Eastern Europe.

Bottom line: .dy8wud is a modern, appliance-first ransomware family with robust cryptography and hybrid extortion.
Priority actions: patch your edge services (Citrix, Fortinet) today, enact strict MFA, and verify that your backup strategy is truly offline and immutable—because once the .dy8wud extension appears, your only reliable friend is a clean restore. Stay safe!