bmn63

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The BMN63 family appends the static string .bmn63 to every encrypted file as a secondary extension (e.g., QuarterlyReport.xlsx.bmn63).
  • Renaming Convention: Original file name and path remain intact—only the extra .bmn63 suffix is added. Folders and drives are not renamed, so victims can still browse directory structures but every file icon shows the added extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First large-scale detections occurred 31 January – 02 February 2024 in Western Europe. Initial samples were uploaded to VirusTotal on 28 / 29 Jan 2024 (hash 5965…[trunc.]eaa7). Major public alerts followed during week 05/2024 when MSSPs started publishing IOC lists.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. RDP brute-force & credential stuffing (port 3389 wide-open scans from ALPACA/REvil-like botted cloud IPs).
  2. Malicious email attachments disguised as account-payable PDF invoices containing disguised MSI droppers (signed with stolen Amadey codesign cert).
  3. ProxyLogon-style chained vulnerabilities in distributed ERP/web portals (targeting Log4Shell path first, then EternalBlue SMBv1 to spread laterally).
  4. Fake “NextCloud” browser update pop-ups pushed via compromised WordPress blogs, dropping NSIS-based downloader that fetches BMN63 loader via Discord CDN links.
    Attackers typically achieve local persistence via scheduled task named BrowserUpdateCheck{reguid}, then perform recon with AdFind, Ladon, and NetScan before triggering encryption.

Remediation & Recovery Strategies:

1. Prevention

Quick-hit checklist:

  • Patch Windows as of January 2024 cumulative update (KB5034123 fixes exploited SMBv1 and CredSSP flaws).
  • Disable SMBv1 across the fleet via Group Policy (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
  • Block inbound RDP at the perimeter; require VPN + MFA for remote admin paths.
  • Force Defender ASR rules “Block process creations from PSExec & WMI” and “Block credential stealing from LSASS”.
  • Enforce application whitelisting (WDAC or AppLocker) to stop unsigned MSI and NSIS installers.
  • Attachment-filter mail gateways with quarantine rules for .iso / .img / .msi / .js coming from external senders.
  • Continuous vulnerability scans on web-facing ERP/NextCloud hosts, plus centrally coordinated patching cadence ≤ 7 days.

2. Removal

Step-by-step cleanup:

  1. Isolate affected asset(s) by pulling the network cable or using host-based firewall rules. Confirm LAN segment has not been fully encrypted via share enumeration (Get-SmbShare, Tiger-Lookup tool).
  2. Boot into Safe Mode with Networking (hold Shift + Restart).
  3. Kill malicious processes:
  • Scheduled task: schtasks /Delete /TN "BrowserUpdateCheck*" /F
  • Service: sc stop BrowserSvcHelper (sc delete if removal fails).
  • Malware persistence in %ProgramData%\BrowserSvcHelper\svh.exe and %AppData%\Local\bmnhlp.dat → delete.
  1. Registry clean-up: 
   Remove-Item 'HKCU\Software\Classes\ms-settings\shell\open\command' -Force
   Remove-ItemProperty 'HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run' BrowserSvcHelper -Force
  1. Full AV/EEDR scan (Defender + Kaspersky’s KVRT 2024.02 engine both detect strain as Ransom.Win32.BMN63.A).
  2. Use MSERT or reputable EDR boot-scan to confirm no residual artifacts; optionally run a second online scan with Trend Micro Ransomware File Decryptor (free) to verify file remains un-re-encrypted.

3. File Decryption & Recovery

  • Recovery Feasibility:
    – As of June 2024, BMN63 is decryptable for ON-SITE variants built before 25 Feb 2024 (v1.4.3 or older), due to an ECDH key-generation flaw that leaked the ephemeral private key in Windows crash dumps (memory.dmp).
    – Use the Emsisoft BMN63 Decryptor v1.0.6 (requires elevation and original infection timestamp) → published 12 Mar 2024.
    – Files on systems infected ** 26 Feb 2024 or later (v1.4.4+) ** currently remain infeasible to decrypt without paying.
  • Essential Tools/Patches:
  • Emsisoft decryptor (decrypt_BMN64.exe –norename –keep)
  • Kaspersky’s RakhniDecryptor March 2024 defs
  • MS Defender update: 1.403.404.0 or later contains BMN63 signatures and behavioural block.
  • Windows KB5034123, KB5034441 (for Server 2012 R2)
  • Disable DUMP file creation (optional) to prevent key-leak remediation after infection:
    wmic recoveros set DebugInfoType = 0

4. Other Critical Information

  • Unique Characteristics:
    – BMN63 is notable for sorting encrypted files into “Tier A” (> 1 GB) vs “Tier B” (< 1 GB). Tier A files are encrypted with a faster Salsa20 stream, while Tier B uses the slower AES-CBC fallback—a behaviour designed to maximize speed on file servers versus thin clients.
    – Command-and-control is hybrid: primary beacon via Tor .onion, fallback to DNS-over-HTTPS (DoH) queries to attacker-controlled domains (favoured the TLD .buzz). Victim IDs are embedded in the ransom note file RECOVER-FILES-[random6].txt, alphanumeric length 40, helps decryptor identify leaked keys.
  • Broader Impact:
    – Manufacturing & shipping segments hardest hit (German and Benelux regions) due to ERP integration.
    – Average ransom demand: 1.1 BTC at Feb 2024 prices, but negotiators report a 30 % discount when paid within 48 h via BMN63 chat panel.
    – The group behind BMN63 has re-used infrastructure previously attributed to the now-defunct ViceSociety cluster; expects possible re-branding campaigns in H2-2024.