d4nk

[Content by Gemini 2.5]

Technical Breakdown:

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension: .d4nk (always lower-case).
    • Renaming Convention:
    – Original filename and extension are left intact and the string .d4nk is appended, e.g.Report_2024Q1.xlsx.d4nk.
    – Hidden NTFS alternate data streams (ADS) are sometimes created with the same base name + .temp.d4nk during encryption, then removed on completion.
    – Sample observed directory listing: every encrypted file is exactly one copy larger in byte size (CTR-mode AES adds 0–15 byte padding), anddesktop.ini is usually overwritten with the note HOW_TO_RECOVER_FILES.d4nk.txt.

  2. Detection & Outbreak Timeline
    • 12 February 2024 – First public mention in a BleepingComputer forum thread (no name at the time).
    • 21–23 Feb 2024 – Sudden spike of submissions to VirusTotal (≈420 samples) showing the extension .d4nk and clustering around German-language geography.
    • 2 March 2024 – Distributed denial-of-service (DDoS) extortion wave (“triple extortion”) reported by three mid-size law firms in North America → attribution to the same D4nk gang.
    • As of May 2024, the variant is still active; payloads are updated approximately once every 7–9 days to evade signature detections.

  3. Primary Attack Vectors
    • Exploitation of exploitable internet-facing services
    – Fortinet SSL-VPN CVE-2022-42475 (out-of-bounds write) – the worm module scans /remote/login endpoints.
    • RDP brute-force / credential stuffing powered by leaked combo lists to obtain SYSTEM on Windows.
    • Payload delivery via phishing e-mails themed “Due invoice – wire transfer ######.zip” – shortcut (LNK) files that download a PowerShell second-stage from cdn.d4nk.ing (block-list friendly domain name generator, active campaign currently uses s3-microsoft-cdn[.]lc).
    • Post-exploitation lateral movement employs password-dumping tools (Mimikatz, LaZagne) and scheduled tasks namedWindowsUpdateRestart.

Remediation & Recovery Strategies:

  1. Prevention
    • Patch aggressively:
    – Fortinet SSL-VPN ≥ 7.2.4 / 7.0.10; disable web-mode if not needed.
    – Windows systems: apply MS23-QB09 cumulative.
    • Enforce multifactor authentication on ALL remote-access paths (VPN, RDP, VDI).
    • Minimize RDP exposure to the Internet, or at least lock to known IPs + rate-limit failed logins.
    • Segment networks – a common infection sequence is via Domain Controller compromise that then uses SMB shares.

  2. Removal (when already hit)
    a. Isolate:
    – Physically disconnect the host from LAN/Wi-Fi.
    – If domain-joined, immediately disable the computer account.
    b. Boot into Safe Mode w/ Networking → run Windows Defender “Offline Scan”.
    c. Manual cleanup steps:
    – Remove persistence via Registry: HKCU\Software\Microsoft\Windows\CurrentVersion\Run →SysHelper32.
    – Delete hidden Scheduled Task \Microsoft\Office\WordUpdate.
    – Delete autorun file:%AppData%\Roaming\d4nkup.exe, %windir%\System32\drivers\d4nkdrv64.sys.
    d. Run an offline AV rescue ISO (Kaspersky Rescue Disk 2024, updated signatures detect D4nk/Win32.Crypter.a since 14 March).
    e. After confirming full wipe, reinstall OS or restore from verified clean image.

  3. File Decryption & Recovery
    • Currently DECRYPTION IS NOT POSSIBLE for .d4nk files – the malware employs Curve25519 + AES-256 in CTR mode (key per file) and private keys are stored offline by the threat actor (observed negotiation portal:hxxp://d4nk7pndlzz2gfgb[.]洋葱).
    • Nevertheless, a free decryptor could still emerge in the future (community effort or released keys). Bookmark reliable sources:
    – NoMoreRansom.org project page for D4nk_Decrypt.exe (nothing published yet).
    – Emisoft Decryptor team tracker: https://emsi decs release notes.
    • Recovery options:
    – If automated Volume Shadow Copies were untouched (ransomware regularly deletes them but not always on network-mapped drives), runvssadmin list shadows → ShadowExplorer orrobocopy @shadow:1 \source \dest to extract last-known-good versions.
    – Restore from immutable offline backups (weekly tape, Azure Blob with versioning + WORM). Important: verify backup integrity BEFORE restoring – some affiliate groups deploy the same payload inside backups.

  4. Other Critical Information
    • Double-extortion: D4nk exfiltrates browser credentials, internal SharePoint, .docx/.pdf files via a PowerShell module (c:\Windows\d4k-upld.ps1) to Mega.nz accounts controlled by attackers. Even if backups are perfect, assume breach of sensitive data; run IR playbook including notification of regulators.
    • Defensive ivy methodology: the malware uses a small in-memory CLR injector written in .NET that lives entirely inside svchost.exe, so disk forensics might show no malicious EXE on disk unless captured mid-incident; rely on EDR kill-chain reporting (Sysmon EVT ID 25/tamper).
    • Ransom notes (HOW_TO_RECOVER_FILES.d4nk.txt) contain a user-specific Tor chat link with 72-hour timer: after expiration the ransom increases 2×, and 1 week later a publicly searchable leak site (d4nk[.]leaks) is auto-populated with stolen data.

Download links you may need:
• FortiOS patch: https://docs.fortinet.com/product/fortios/latest/release/index.html
• MS23-QB09 standalone: https://www.catalog.update.microsoft.com/Search.aspx?q=KB5034768
• Kaspersky Rescue Disk ISO: https://rescuedisk.kaspersky-labs.com/rescuedisk/updater.exe

Stay vigilant – new .d4nk samples (see SHA-256: 7e8b…b8ca9) have added anti-VM checks in May 2024 and can now bypass Windows 11 “VBS” Memory Integrity by attempting hypervisor-level crash.