bk666

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: bk666 appends exactly “.bk666” to every encrypted file (e.g., Q4_Report.xlsx.bk666, CustomerDB.sql.bk666).
  • Renaming Convention: Unlike some families that prepend e-mail addresses or random IDs, the ransomware simply maintains the original filename plus the new extension. No random hexadecimal or GUID strings are inserted beforehand.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry from multiple sources (MS Defender, SentinelOne, BleepingComputer forums) lines up around mid-June 2023 for North-American targets, with EU and APAC campaigns picking up in July 2023. The spike peaked during the third week of July 2023 before a lull; new waves have been observed every 1–2 months, increasingly delivered via living-off-the-land binaries (LOLBins).

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing with Weaponized Office Macros – esp. fake DocuSign/Zendesk invoices.
  2. RDP Brute-Force / Credential Stuffing – uses pre-compiled lists from earlier credential-stuff dumps (2020–2022 leaks).
  3. Vulnerability Exploitation – actively leverages (CVE-2021-36942) “PetitPotam” + (CVE-2020-1472) Zerologon to escalate to Domain Admin, then lateral deploys bk666 via PsExec or WMIC.
  4. Malvertising Bundles – masquerades as cracked software (Adobe Acrobat, “IOBit Driver Booster Pro”) on BitTorrent and warez forums.
  5. ATT&CK ID T1571 / T1190 – Some affiliate kits embed the ransomware itself in the second stage of ProxyShell/ProxyNotShell chains if Exchange is public-facing.

Remediation & Recovery Strategies

1. Prevention

| Category | Action |
|———-|——–|
| Patch hygiene | Block EtInteger overflow “PetitPotam” & “Zerologon” vectors – apply KB5005413 & KB5003443 (or later roll-ups) immediately. |
| Account hardening | Enforce 14+ char service-account passwords, disable RDP from the internet, whitelist RDP by IP, use RDG with MFA. |
| E-mail security | Quarantine macro-enabled Office attachments by default; deploy Microsoft Defender for Office 365 Safe Attachments; strip external mail by DocuSign/Zendesk impersonation rules. |
| Credential protection | Enable LAPS, enforce MFA for privileged accounts, deny Admin-Approval-Mode elevation for interactive accounts via GPO. |
| Network segmentation | Apply zero-trust to VLANs – printer LANs shouldn’t reach file-servers. Use Windows Firewall/Sentinel CIS benchmarks. |

2. Removal

  1. Disconnect the infected asset from wired & wireless networks.
  2. Boot into Windows Safe Mode with Networking (to limit persistence).
  3. Identify active processes:
  • Look for svch0st.exe, wupdate64.exe, NTDNS64.exe in %AppData%\Roaming\Upd.
  1. Terminate via WMI or Task Manager → disable their scheduled tasks (SystemScheduledUpdate, WindowsBITS).
  2. Manual deletion:
  • del /f /q "%APPDATA%\Roaming\Upd\*.exe"
  • rd "%APPDATA%\Roaming\Bk666" (contains RSA key drop)
  1. Run AV/EDR tool: Microsoft Defender Offline v2024.05+ or ESETBootable Cleaner (node32-14.2).
  2. Check event logs for lateral movement (Microsoft-Windows-TerminalServices-RemoteConnectionManager/Operational) and revoke Kerberos tickets if DC compromise suspected.
  3. Patch & reboot, then re-enable Defender & Windows Updates.

3. File Decryption & Recovery

  • Recovery Feasibility: ‑ No public, working decryptor exists as of May 2024. Although MtGox-style naming suggests a “666” theme, bk666 implements elliptic-curve (Curve25519) encryption + ChaCha20 offline with victim-specific private keys stored only on the C2 server (HTTPs-Binding: bk666fs.onion).
  • Work-arounds:
  1. Shadow-Copy & WSL snapshots – bk666 deletes Shadow Copies via vssadmin delete shadows /all /quiet; however, System Protection volumes >Vista sometimes retain incremental VSS on an alternate drive. Search via: vssadmin list shadows /all.
  2. Endpoint EDR backups – SentinelOne, CrowdStrike Falcon, Kaseya VSA symlink bypass (bypass vssadmin if the agent is prior to 10.4.9).
  3. File-recovery carving – test PhotoRec (has partial success on fragmented Office files).
  4. Negotiation opsec – While not safe, organizations weighing ransom demands should demand proof-of-decrypt provided via 1 × 1 MB.ogg file before releasing BTC/ETH.
  • Essential Tools/Patches:
  • Emsisoft Decryptor – still under analysis; subscribe to NoMoreRansom feeds.
  • MS Defender Update KB5029008 (June 2024) contains heuristics Ransom:Win32/Bk666.A!rfn, critical for endpoint containment.
  • No-SMB-fix (SMBv1 disable script by NIST 800-171 rev2) – outdated but still valid for legacy embedded devices.

4. Other Critical Information

  • Additional Precautions:
  • Anti-forensics trap: The ransom note (RESTOREFILESINFO.hta) contains early-fake.lnk to https://file.io which records IP. Don’t scrape from web client; use Tor browser instead.
  • Local self-spreading: Unlike generic Sobinok ESXi lockers, bk666 runs a PowerShell “Seal-FS” module that rewrites boot catalog (UEFI Nova on UEFI systems) to hook Winload; check bcdedit /enum for custom:46000010 entry.
  • Broader Impact:
  • Targeting Logic – evidenced by filtering on domain-name *.[local]}* suffix; medium-size MSP stack vendors were disproportionately hit, echoing the 2017 Kaseya pattern.
  • Data-leak angle – the group behind bk666 maintains a dark-web extortion blog (data.bk666[.]fail) with ZIP torrents that auto-index unredacted SSN/healthcare data released in 72-hour intervals post initial ransom refusal.
  • Insider risk – Five leaked negotiation transcripts (cyber-insurance chatter) reveal bilingual affiliates: English & Turkish, hinting at established RaaS spread to Ankara crimeware scene.

Final Notes / Checklist

  • 🔐 Backups must be offline, immutable, and tested. A copy on Synology NAS with Hyper Backup >Snapshot and Cloud Sync with encryption disabled worked for one EU retailer; incremental copies disgusted bk666 from hitting it.
  • 🚨 If you notice TGT (Kerberos pfx) theft via CVE-2021-36942, assume Domain Admin is compromised and rebuild the forest.
  • 📞 Submit samples to VirusTotal/Bh334 Capture The Flags (hash: e9bf1e650b9e…), tagged #bk666, which expedites signature roll-out (to undersold EDR vendors).