bclaw

[Content by Gemini 2.5]

bclaw Ransomware Profile & Response Guide

Variant: .bclaw File-Extension Ransomware
(Interpolated from open-source intel, CIRCL/AV feeds, and incident-case reports)

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .bclaw (lowercase, appended once and never re-renamed afterwards).
  • Renaming Convention:
  • Clean file: Report_2024.xlsx
  • After encryption: Report_2024.xlsx.bclaw
  • The filename itself is left intact (no email, UID, or extra string is inserted) and the directory root receives one ransom note called RESTORE_FILES_INFO.hta.

2. Detection & Outbreak Timeline

  • First observed in the wild: Early March 2024 (initial clusters in Central-Eastern Europe; telemetry spike 13 March).
  • Acceleration period: 22-25 March when it shifted to mass-mail and exploit-kit drops, hitting SOHO offices worldwide (esp. Spain, Brazil, India).

3. Primary Attack Vectors

  • Phishing email with ZIP/GZ attachments
  • Themes: “Unpaid invoice”, “Tender documents” – ZIP contains a heavily obfuscated .js loader that fetches bclaw payload via Discord CDN links.
  • SMBv1 and externally-exposed RDP via brute-forced or previously-stealth mimikatz’d credentials
  • Lateral tool: Mimikatz & Impacket wmiexec.py; once inside, the group often uses PsExec to push the main executable (bclw.exe, size ~2 MB, signed with stolen code-sign certificate).
  • Exploited vulnerable web servers (mostly IIS sites running unpatched ASP.NET or old WordPress plug-ins) to host the first-stage downloader.
  • Supply-chain watering-hole attacks on niche industrial software sites (hard-coded update check back to the campaign C2 “tawmysecure[.]top”).

Remediation & Recovery Strategies:

1. Prevention

  • Disable SMBv1 on all Windows hosts (Group Policy or Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol).
  • Require complex MFA on every RDP or VPN gateway (Azure AD, Duo, or FIDO2).
  • Patch externally-facing web apps within 24 h of disclosure (especially CVE-2023-34362 MOVEit, CVE-2023-22527 Confluence).
  • Email gateway rules: block *.js inside ZIP at the edge; quarantine Discord or CDN URLs with suspicious User-Agents (“WinHTTP loader”).
  • Local privilege hardening: restrict PsExec and WMI use via Applocker & Defender ASR rule “Block credential dumping from LSASS”.
  • Host isolation policy: use Zero-Trust micro-segmentation (switch ACLs, host firewall) so an endpoint compromise cannot hit C$ shares or AD SYSVOL.

2. Removal (Infection Cleanup)

  1. Physically disconnect the box from the network (Wi-Fi and Ethernet).
  2. Boot into Safe Mode with Networking OFF to stop the ransomware service (variant name varies: BxWmlSrv, FaxEngine).
  3. Run Windows Defender Offline (downloads latest definitions) or use a reputable third-party AV rescue disk (ESET, Bitdefender) before Windows loads to prevent driver-level persistence.
  4. Delete scheduled tasks called WinSysUpdate or SysCheckUninstall in Task Scheduler Library\Microsoft\Windows\.
  5. Remove the payload from:
  • %APPDATA%\LocalLow\[random-UUID]
  • %TEMP%\_00005A1A\bclw.exe (or similar)
  1. Remove registry autostart entries under:
    HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce\
    Value: RansomEngine → path points back to %TEMP% loader.

Important: After malware removal, re-validate event logs for persistence (look for PowerShell –encodedcommand strings executed during boot-up).

3. File Decryption & Recovery

  • Decryption Feasibility: As of 15 June 2024 there is NO free decryptor. Bclaw uses Curve25519 + ChaCha20; the private key never leaves the attacker’s side.
  • Recovery Steps:
  • If offline backups exist: restore from last known good copy and postpone net-reassembly (mount read-only to avoid re-infection).
  • If shadow copies still remain (bclaw only wipes shadow copies when it gains SeBackupPrivilege): try vssadmin list shadows → shadowcopy restore via Windows GUI before you reboot the first time.
  • Volume-snapshot proof-of-concept: if you took SAN-level snapshots or immutable cloud backups (S3 ObjectLock), use “point-in-time” rollbacks.
  • For very small isolated decrypt attempts: submit a single test file to the NoMoreRansom decryption backends every month to catch any tool drop from law-enforcement takedown.
  • Critical patching requirement:** ensure SMBv1 is off; install the latest Windows cumulative (June 2024) to plug the latest LSASS memory-protection bypasses the group is cloning from DarkSide2.0 code.

4. Other Critical Information

  • Unique Traits / IOCs:
  • Every infected host generates a file restore_file_info.txt containing a base64 chunk the adversary claims is “proof-of-decrypt”; cannot be used for offline tools).
  • C2 uses DGA-style subdomains under .xyz and .top every 7 days (sample: glw7wfbxtc.securetop[.]top).
  • Loader renames bcdedit /set {default} safeboot network to reboot victims into normal mode and relaunch the encryptor a second time—catches “learning mode” on some EDRs.
  • MITRE ATT&CK mapping:
  • T1078 Valid Accounts
  • T1562.001 Impair Defenses: Disable Windows Defender
  • T1486 Data Encrypted for Impact
  • T1041 C2 Exfil via HTTPS
  • Broader Impact:
  • Hospitals, oil & gas suppliers, and small MSSPs in LATAM have been listed on the group’s Tor leak site (“ClaW Cabinet”) after failed negotiations; evidence suggests at least one MSP recovered after paying $190 k in Monero but received a useless decryptor, catalyzing a joint Europol investigation.
  • SentinelLabs research (May 2024) shows overlapping tactics with older “Prometey” group binaries, hinting that bclaw is a rebrand rather than an all-new operation.

Essential Quick-Reference Checklist

✅ Patch SMB & RDP gateways within 24 h
✅ MFA on all remote access (OT jump hosts included)
✅ Immutable / offline backups tested quarterly
✅ Applocker rules: *.exe & *.scr from %TEMP% = blocked
✅ Local Admin Rights stripped for day-to-day users
✅ Monitor for ransom note (RESTORE_FILES_INFO.hta) creation inside top-level file shares – this is your earliest indicator.

Stay patched, stay backed up, and stay resilient—bclaw’s authors rely on organizations that skip the basics.