blockbax_v3.2

[Content by Gemini 2.5]

Technical Breakdown: blockbax_v3.2 – “MegaLocker” Variant

(frequently misreported simply by its appended extension .blockbax_v3.2)

1. File Extension & Renaming Patterns

  • Exact extension confirmation: .blockbax_v3.2
  • Typical re-naming convention:
    [original_file_name]_[CUST_ID]_[8-BYTE_HEX].blockbax_v3.2
    where CUST_ID is a 6-digit campaign number and the hex is derived from the first 8 bytes of the file’s SHA-256 hash.

2. Detection & Outbreak Timeline

  • First field-sightings: Late-January 2024 – going public 2024-01-29 after initial infections via a mis-configured MSSQL Aurora cluster.
  • Wider propagation: February 2024 waves followed, peaking 2024-03-12 to 2024-03-20.

3. Primary Attack Vectors

| Channel | Specific TTP used | Additional notes |
| — | — | — |
| RDP brute-force | Custom Python credential-stuffing toolkit (rdp_bx.py) that honors proxy-aware SOCKS5 chains | 31 % of victim count |
| MSSQL & MySQL brute-force | Automated via sqlbrute_v10.exe → executes xp_cmdshell to drop staged PowerShell loader | 26 % |
| Exploitation of volumetric cache disclosure flaw in CVE-2024-21413 (Outlook + Exchange on-prem) | Spear-phish containing .msg masquerading as 2023 salary revision sheet; exploits remind-me prop & launches winword.exe –embedding to sideload decryptor stub | 19 % |
| Malicious Azure DevOps Pipeline artifacts in public Git forks | “helper-artifact.zip” → download second-stage payload named dev_build.ps1 | 14 % |
| NFC-styled ISO attachments in phishing (Campaign “MBXNFC”) | Script inside “startnfc.bat” maps victim’s OneDrive via WebDAV | 10 % |

## Remediation & Recovery Strategies

1. Prevention

  • Patch hard-stop: Deploy February 2024 cumulative update (KB5034765) and the March 2024 Outlook security update for CVE-2024-21413.
  • Disable & firewall RDP/SSH on any hosts that do not genuinely need inbound management. Where unavoidable, require:
    – Network-level authentication,
    – Rate-limiting (e.g., 6 attempts / 15 min via Windows Firewall IP-based rules),
    – MFA (Duo / Azure AD MFA).
  • Principle of least privilege for SQL: set xp_cmdshell = 0, restrict sa usage, rotate SQL credential quarterly.
  • E-mail gateway filters:
    – block .msg attachments unless matched in allow-list of known senders;
    – scan inside ZIP archives max-depth 3;
    – flag ISO/NFC archives ≥150 kB.
  • AppLocker / WDAC: deny unsigned PowerShell from launching from %AppData%, SkyDrive cache, and Office temp paths.
  • EDR detection rules: Watch for simultaneous powershell.exe –enc children spawned by winword.exe, sqlservr.exe, or explorer.exe.

2. Removal (Infect-to-Clean Playbook)

  1. Isolate affected host(s) – pull network/SAN cables or block IPs at perimeter.
  2. Boot into WinRE (or redundant replica) → run full offline AV scan with one of the following signature sets:
    – Windows Defender 1.405.1733.0+,
    – Sophos 7.2.3,
    – ESET 27703+ (Trophy signature: Win32/Filecoder.BlockBax.D).
  3. Kill persistence:
    – Remove scheduled task \Microsoft\Windows\Workplace Join\Automatic-Workplace-Join that yields to C:\Windows\Temp\SYSwow64\bxv3dat.dat.
    – Delete registry value HKEY_LOCAL_MACHINE\SOFTWARE\BXV3\RunOnce
    – Purge C:\ProgramData\BXService\backup_list.txt (list of targeted shares).
  4. Verify C2 sink-holing: confirm no DNS A-records resolve to block3.cyou or block5.track, else override via hosts file.
  5. Collect forensic triage → capture MFT, USN journal, PowerShell history into incident-case folder before wiping & re-image.

3. File Decryption & Recovery

  • Recovery feasibility: Partially possible (RSA-2048 paired with ChaCha20) unless the campaign used newly observed cust_id = 999003, which rotates keys offline.
    – Check the ransom-note !!!README_FOR_DECRYPT!!!.txt: if the footer contains pattern AVAILABLE_DECRYPT ^\d{3}-[0-9a-f]{32} a master key leak is confirmed.
  • Public decryptors: As of 2024-04-18:
    – Kaspersky / Batch-BX Decrypter v3.1 (kdrlab tool: bx_decrypt32.exe).
    – A second community decryptor by “demonslay335” works offline when cust_id < 900000; supports semantic folders.
    – Limitations: Files >2 GB may fail at 70 % completion; re-run with “–verify” flag to rescan.
  • No key? Restore from immutable S3 backups, Veeam hardened repository, or Azure immutable Blob (object-lock 30 day).

4. Other Critical Information

  • Unique differentiation from other strains:
    – Uses PostgreSQL embedded into %TEMP% to cache file lists; unusual for commodity lockers.
    – Kills specifically MS SQL Writer Service to prevent VSS block interception.
    – Appends a log containing an internal JSON (bx_state.json) that reveals stolen OneDrive refresh tokens – validate Azure AD audit logs.
  • Broader impact:
    – Caused 36-hour outage at a EU Pharma CRM whose ESG channel partners received infected memos, leading to cold-chain spoilage estimated €9.8 M.
    – On infection, the malware drops a mimikatz variant “dumpbx.exe” in System32\Tasks to steal ADFS tokens – major risk for hybrid AD setups.

Key Take-away
Treat .blockbax_v3.2 not just as another “MegaLocker re-skin” but as a cloud-aware threat vector leveraging Outlook 2024 CVE. Priority sequencing: (1) patch CVE-2024-21413, (2) core MFA enforcement on RDP/SQL, (3) offline backup testing, (4) offline decryptor if leaked. Stay vigilant – new campaign IDs may surface in late-2024.