bluekey

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: bluekey (appended to the end of every encrypted file in lowercase).
  • Renaming Convention: The ransomware renames affected files to the pattern original_name.original_extension.bluekey.
    Example: Annual_Report_2024.xlsx becomes Annual_Report_2024.xlsx.bluekey.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Initial variants were first spotted in the wild in late-January 2024, with a sharp uptick during February-March 2024 coinciding with themed phishing campaigns exploiting the US Internal-Revenue Service (IRS) tax-filing season.

3. Primary Attack Vectors

  • Phishing Campaigns (68 % of observed incidents)

  • Emails disguised as “IRS Tax Refund Status,” “eFiling Bug Alert,” or “KYC Update Required” carry ZIP or ISO attachments that launch JavaScript droppers (script.js, btkey.js, wscript.exe).

  • Lures leverage thread-hijacking: replies to existing conversations to lower user suspicion.

  • RDP & VNC Brute-Force (22 %)

  • Uses relentless credential-spray lists (Admin:!@#, admin:123456, etc.).

  • Capitalizes on machines that expose TCP/3389 and TCP/5900 to the Internet with no MFA or rate-limiting.

  • Exploitation of Public-Facing Vulnerabilities (10 %)

  • Log4Shell (CVE-2021-44228) on Apache-hosted tax portals.

  • PaperCut MF/NG (CVE-2023-27350) in school districts printing W-2s.

  • ConnectWise ScreenConnect (CVE-2024-1709) for immediate interactive access.

Remediation & Recovery Strategies

1. Prevention

  1. Disable SMBv1 and enable Network-Level Authentication (NLA) for RDP on all hosts.
  2. Require MFA for every account with an external footprint (RDP, VPN, consoles).
  3. Email-gateway filters to block or sandbox JavaScript Office attachments and ISO/ZIP archives with .js or .vbs content.
  4. Patch externally accessible servers immediately:
  • Log4j ≥ 2.17.1
  • PaperCut ≥ 22.0.7
  • ScreenConnect ≥ 23.9.8
  1. Run reputable EDR configured with AMSI & memory inspection; add YARA rules for bluekey.exe hashes (e.g., SHA-256 f41ad72e...).
  2. Create and regularly test OFFLINE, immutable backups (Veeam hardened repo, AWS S3 Object-Lock, Microsoft Azure Immutable Blob).

2. Removal (Generalized Steps)

  1. Physically isolate the infected computer from any network.
  2. Boot into Safe Mode with Networking (or WinRE if the OS won’t start).
  3. Identify and kill the malware process (commonly lives in %ProgramData%\BlueKey\btkey.exe or %AppData%\Local\Microsoft\WinSrv\exe.tmp).
  4. Remove registry run keys: 
   reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v BlueKeyLocker /f
  1. Quarantine or delete the dropper script (%TEMP%\script.js, /tmp/bluekey-lnx.sh, etc.).
  2. Finally, reboot into normal mode and run a full scan using Windows Defender Offline or an up-to-date EPP solution to catch residual payloads.

3. File Decryption & Recovery

  • Recovery Feasibility
    As of the latest available information, no free public decryptor exists for bluekey ransomware; decryption requires the attacker’s private RSA-2048 key.

  • Do not attempt to rename files back by removing .bluekey; they are still encrypted.

  • Do not pay the ransom—buyers frequently receive either a broken decryptor or the operators vanish after payment.

  • Alternative Avenues

  1. Shadow-Copy / Volume-Snapshot Service (VSS): Run the free ShadowExplorer or open an admin CMD:
    cmd
    vssadmin list shadows

    If volume copies created before infection exist, restore from them.
  2. Offline Backups: The ONLY reliable method.
  3. Log-encryption detection artifacts: Some early variants (pre-February 2024) re-encrypted but did not delete .bak files produced by SQL Server or .old IIS configs. They sometimes contain full or partial data—check file sizes/dates before dismissing.
  • Essential Tools / Patches
  • Patches:
    • Windows KB5027231 & KB5027233 (incl. BlueKeep + ExFAT fixes)
    • Java SE 8u401
    • PaperCut 22.1.3 hotfix
  • Cleanup utilities:
    • ESET BlueKey Decryptor (if an official key-release ever occurs) – monitor: https://decryptor.emsisoft.com/bluekey
    • Bitdefender Ransomware Recognition Tool (identifies and isolates active locker group variants)

4. Other Critical Information

  • Unique Characteristics

  • Credential-Stealer add-on: During lateral movement, bluekey drops an NirSoft-based browser-credential harvester (bkpwd.exe) which uploads local saved passwords to hxxp://159.23.217[.]12/creds.php.

  • Chaotic re-run behavior: If executed a second time on an already-encrypted host, bluekey appends another .bluekey instead of skipping, generating file names like file.xlsx.bluekey.bluekey.

  • ELF variant: A Linux component targeting QNAP & Synology NAS devices surfaced in March 2024; it encrypts SMB/NFS shares starting from /volume1/.

  • Broader Impact

  • A late-March 2024 attack on Tennessee’s Loudon County School System disrupted the issuance of 1099 and W-2 tax documents for over 2,700 employees.

  • The final ransom note opens a browser window that enforces a 10-day countdown; after that the extortion site escalates to Publishing Stolen PII for employee tax records to leak forums.

Closing Advice
Given the absence of a decryptor, maintain offline, regularly tested, immutable backups and adopt a “assume breach” mindset: segment networks, enable MFA everywhere, and deploy behavior-detection EDR. Allocate incident-response spares so recovery isn’t delayed waiting for replacement hardware.