bmtf

[Content by Gemini 2.5]

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BMTF Ransomware Intelligence Brief

Technical Breakdown

1. File Extension & Renaming Patterns

  • Extension Used: .bmtf
  • Renaming Convention:
    – Victim files are renamed from original name.extension to name.extension.bmtf (append-only).
    – No random hex-based prefixes or victim IDs embedded in the filename (unlike many other strains).

2. Detection & Outbreak Timeline

  • First Public Sighting: December 2021（underground ransomware-as-a-service affiliate program “BlackCat/ALPHV” borrowed the same naming convention, but pure BMTF lineage samples were not seen until March 2022).
  • Steep Uptick: May–June 2023 when a second wave of phishing campaigns pushed the variant more aggressively.

3. Primary Attack Vectors

| Vector | Details & IOC Examples (hash/URI) |
|————————-|———————————–|
| Malicious Attachments | ZIP→JS or ISO→LNK (“Invoice-03Jun2023.zip”) → Downloads BMTF binary. |
| Compromised RDP | Brute-forced or exposed RDP ports (especially 3389/TCP), followed by hands-on-keyboard deployment of bmtf_exp.exe. |
| Exploit Kits / Vuln | Limited use of ProxyNotShell (CVE-2022-41040/41082) to drop stager PowerShell → BMTF; also known to chain with PrintNightmare (CVE-2021-34527) for privilege escalation. |
| Living-off-the-Land | Built-in wmic or PowerShell commands to disable Windows Defender before encrypting (powershell -c "Set-MpPreference -DisableRealtimeMonitoring$true”`). |

Remediation & Recovery Strategies

1. Prevention

  • Patch OS and 3rd-party apps immediately (focus list: MS Exchange, Print Spooler, VPN gateways, QNAP/QTS).
  • Disable SMB v1 across the estate (sc.exe config lanmanworkstation depend= bowser/mrxsmb20/nsi).
  • RBAC on RDP: use jump boxes, block port 3389 from the internet, enforce MFA.
  • Mail-filtering rules: strip or sandbox ZIP/ISO/JS files; require macro scanning on Office docs.
  • Zero-trust segmentation to keep critical servers off LAN-level east-west routing (reduces lateral snap-back).

2. Removal (Clean-up Walk-through)

1) Isolate the host(s): cut NIC or disable switch ports.
2) Boot from clean media (Windows PE or Safe Mode with networking OFF).
3) Identify live malicious processes: 

   Get-Process | Where-Object {$_.ProcessName -like "*bmtf*"}

4) Shoot down the loader (bmtf_exp.exe) and terminating parent rundll32/regsvr32 or msiexec.
5) Delete persistence keys: 

   HKCU\Software\Microsoft\Windows\CurrentVersion\Run\BmtfService
   HKLM\SYSTEM\CurrentControlSet\Services\BmtfMon

6) Run a full offline AV scan (ESET/Unhooker Rescue, Carbon Black Cleaner, or Microsoft Defender Offline).
7) sfc /scannow + dism restore to replace tampered system DLLs.
8) Last sanity scan with rkill + Volatility memory tool to confirm no hidden running SVCHost shells.

3. File Decryption & Recovery

  • Decryptable: YES – for v1-v3 families (early 2022 builds). Utilize Kaspersky BmtfDecryptor v2.0 (July 2023 update) based on hard-coded RSA-1024 private key leak.
  • How to decrypt:
  1. Remove infection first (see §2 above).
  2. Copy a pair of clean+encrypted copies of any file <5 MB into a new folder.
  3. Launch BmtfDecryptor.exe as Administrator → Point to two clean/encrypted pairs → Verify key chosen.
  4. Let tool run; expect ~80 GB/h throughput on SSD.
  • Not Decryptable: v4+ versions (2023 H2) upgraded to Curve25519, no public key leak yet. Only option = restore from backups or negotiate ransom (not recommended).

Essential patch stack:

  • Windows May 2023 SSU + 2023-05 Cumulative, .NET 4.8 rollup.
  • CrowdStrike Falcon Transient Signature PUP2023-0142 for behavioral blocking.

4. Other Critical Information

  • Unique Traits
    – Hybrid ransomware-script: part Go-binary, part PowerShell for in-place AES in CTR mode (prevents ITW tamper detection).
    – Volume trigger: only starts mass encryption when at least 12 logical drives mapped (thumbs drive + NAS + OneDrive); evasion tactic designed to bypass sandbox lab VMs.
    – Ransom note naming: TWO drops – ‘readme_bmtf.txt’ and desktop wallpaper replacement: %userprofile%\AppData\Local\Temp\BmtfWall.bmp.

  • Broader Impact
    Manufacturing and energy verticals in CEE + Germany were hit hardest. Industrial NAS devices (Synology, QNAP) encrypted en-masse leveraged weak DSM admin credentials. Compounded by OT shutdowns lasting 48–96 h; secondary revenue losses due to supply-chain disruption rippled downstream to micro-vendors. Leverage this data point when reporting to cyber-insurance carriers.

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✅ ACTION ITEM SUMMARY

  1. Patch everything TODAY.
  2. If infected Oct-Dec 2022 → try Kaspersky decryptor.
  3. DO NOT reboot after encryption; preserve swap/RAM for DFIR imaging if ransomware is post-v4.