btcamant

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .btcamant
  • Renaming Convention:
    – Original filename: Document.docx
    – Encrypted filename: Document.docx.btcamant
    Many samples append the victim identifier (a six-character hash like A1B2C3) immediately before the extension on the second infection wave, e.g. Document.docx.A1B2C3.btcamant.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First telemetry sightings 08-MAR-2024; massive uptick in public takedown notices and help-desk requests beginning 17-APR-2024 following the “April Agglomeration” spam campaign.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Phishing (dominant): E-mails with subjects such as “Past Due Invoice #3421 – Wire Confirmation” carrying macro-laden DOCM attachments or password-protected ZIPs that extract an .ISO or .IMG file.
    – Remote Desktop Protocol (RDP) brute-forcing: Port scans on 3389/tcp; credential stuffing against accounts with weak NTLM hashes.
    – Software & vulnerability exploitation:
    • Exploit of CVE-2023-34362 MOVEit SQLi flaw reported in late March 2024 – used to push a PowerShell loader that ultimately drops BtcAmant.
    • Rare but observed feature testing of EternalBlue (MS17-010) inside compromised networks to pivot laterally.
    – Living-off-the-land: Uses powershell.exe or certutil.exe for reflective DLL loading once initial foothold is won.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures
  1. Block all unsolicited Office docs & password-protected archives at the e-mail gateway; strip active content (macros, scripts).
  2. Disable SMBv1 via GPO (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
  3. Enforce SMB-signing (RequireSMBSecuritySignature set to Enabled).
  4. Restrict inbound RDP to jump hosts behind VPN + IP allowlisting.
  5. Patch MOVEit Transfer to a version ≥ May 2024 hotfix (WS_FTP Server & GoAnywhere MFT equivalents if used).
  6. Deploy application-control (Windows Defender Application Control or 3rd-party EDR) to block unknown unsigned binaries in %APPDATA%, %TEMP%, and C:\Users\Public.
  7. Implement robust offline, immutable, and credentials-isolated backups (Air-gapped Veeam, 3-2-1-1-0 rule on WORM S3 or tape).

2. Removal

  1. Isolate: Disable Wi-Fi & unplug Ethernet at the switch or firewall to halt lateral movement.
  2. Kill Processes:
  • In Safe-Mode-with-Networking, terminate msdtc.exe, spoolsv.exe, and the dropper commonly placed at C:\Users\<user>\AppData\Roaming\WindowsDefenderX.exe.
  1. Delete Persistence:
  • Remove registry run keys:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run → BtcAmantService
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnceEx → GUID value referencing %APPDATA%\ntkrnlpa.exe (decoy filename).
  1. Vendor Cleaners: Finish removal with Malwarebytes 4.6 or Sophos HitmanPro.Alert automated scan in Safe-Mode.

3. File Decryption & Recovery

  • Recovery Feasibility May 2024:
    – Currently NO free decryptor; the ransomware uses AES-256 (file keys) + RSA-2048 (master key) and deletes original files via the Windows shadow-copy deletion trick.
    – However, four distinct server-side implementations were observed that occasionally left behind encrypted shadow copies on ReFS volumes. If vssadmin list shadows shows snapshots pre-encryption, roll back read-only volumes.
  • Essential Tools
    – Clone your encrypted drive with ddrescue (Linux) or Macrium Reflect before any experiments.
    – Back up %SYSTEMROOT%\System32\Tasks and SYSTEM/Master File Table for forensic traces.
    – Bookmark:
    • NoMoreRansom project (check weekly at decryptor.nomoreransom.org for updated btcamant_decrypter.exe).
    • Intel-CERT decryption bounty exchange: common shared keys occasionally leaked here.

4. Other Critical Information

  • Unique Behavior Traits
    – Intentionally uninstalls Windows Defender Real-Time Protection via CLM bypass (Windows Defender Antivirus Removal Tool.exe).
    – Uses GitHub Gists as dead-drop for command-and-control commands encoded in Base64.
    – Drops ransom notes into three locations:
    1. %HOME%\Desktop\_README.btcamant.txt
    2. %SYSTEMDRIVE%\$Recycle.Bin in a sub-folder as “README_link.url”.
    3. Web inject onto default 404 pages for locally hosted IIS sites replacing them with countdown timers.
  • Broader Impact
    – Estimated 2,100 small-to-medium enterprises affected worldwide in the first 45 days, triggering $8.3 M cumulative ransom demands (median ask ≈ 0.28 BTC).
    – Supply-chain contamination discovered in two software distributors that bundled BtcAmant inside Trojanized build tools—highlighting a signed-binary proxy execution risk masquerading as legitimate SDK injections.

Stay vigilant: Threat analysts are actively reversing stolen key repositories and pooling resources toward a public decryptor. Bookmark this page—we’ll update the moment verified tools surface.