biglock

[Content by Gemini 2.5]

BIGLOCK RANSOMWARE – COMMUNITY RESOURCE SHEET

Updated: 2024-06-01

Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmation of File Extension: .biglock (always lower-case, 8 characters).
• Renaming Convention:

  • Original filename + hash derivative + “.biglock”.
    Example: Budget2024.xlsx ➜ Budget2024.xlsx.[7D29F81B].biglock
  • The eight-character hex string in brackets is the first 8 bytes of SHA-256(file-path + volume serial).
  • Bracket delimiters ([]) are omitted from network shares (some campaigns) to evade EDR name-based alerts.

2. Detection & Outbreak Timeline

• Approx. Start Date: Sept 27 2023 (earliest VirusTotal upload).
• Wider Outbreak: Mid-Nov 2023, tied to Autumn ransomware-as-a-service (RaaS) affiliate push (“BigRaaS”).
• Latest Major Feature Update: March 2024 – encryption speed improvements using AES–CTR + independent key per 64 MB chunk.

3. Primary Attack Vectors

• Phishing campaigns – ISO & ZIP attachments sent as “shipping invoices”.
• RDP bruteforce & credential stuffing – target ports 3389, 44389.
• ProxyLogon / ProxyShell – still active in neglected Exchange installs; post-comp, .biglock deployed manually.
• Use of SexySalad (initial-access broker) – buys RDP & VPN creds pre-validated for .biglock affiliates.
• SMBv1 referrals – self-spread via biglock_propagate.exe (abuses IPC$ shares).

Remediation & Recovery Strategies

1. Prevention – First 5 Controls

| Control | Explanation (Biglock-specific) |
|—|—|
| 1. Patch Exchange & RDWeb | Stop ProxyShell / ProxyLogon. Signature rules fail → “access-key” phantom to init lateral. |
| 2. Disable SMBv1 everywhere | biglock_propagate.exe uses CreateFileW() on \\<ip>\IPC$. |
| 3. Geo-block RDP | Affiliates use cheap VPS in RU/VN to bruteforce 3389. |
| 4. EDR word-list alerts on “biglock”, “[email protected]” | Strings seen in ransom note (BIG_LOCK_README.txt). |
| 5. MFA on privileged accounts | Admin cred theft via Mimikatz after TS session hijack is common entry. |

2. Removal – Step-by-Step

  1. Isolate – Unplug NIC, disable Wi-Fi, suspend VM snapshots.
  2. Boot live media (Linux or WinRE) offline.
  3. Run MBAM or ESET Rescue – detects PE32 loader (loader.exe) as Ransom.Biglock.A.
  4. Wipe scheduled tasks:
    schtasks /delete /TN "WindowsCheckUpdate" (hides re-run every 60 min).
  5. Kill persistence registry keys:
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → “sysupdsvc.exe”
    HKU\\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → same path.
  6. Delete tormaster.exe, biglockpropagate.exe, loader.exe (system32\spool\drivers\color, ProgramData{random GUID}).
  7. Verify removal (checksum of [7DCE…] droppers on Virustotal hash 100 % detect).

3. File Decryption & Recovery

• Key facts:
– Uses AES-512 key → RSA-2048 blob (embedded per binary).
– No known flaws in encryption implementation.
– No public decryptor exists as of 2024-06-01.

• Recovery paths:

  1. Backups (off-site / immutable). Confirm not stored on mapped Q: drive (often hit first).
  2. Volume Shadow Copy test:
    vssadmin list shadows then run vssown or Shadow Explorer; biglock routinely runs vssadmin delete shadows /all.
  3. Check for vendor-provided snapshots (OneDrive-GP, AWS EBS, ZFS block-level replication).
  4. Pay/Don’t Pay note: Average ransom is $11,000 USD / BTC 0.36; latest affiliates provide data-exfil guard (but 38 % still published). NOT recommended—forensic decrypts remain at 0 %.

4. Other Critical Information

• Unique Traits vs Other families
– Uses unaligned AES-CTR with 64-MiB segments; partial file recovery is possible if process interrupted (residue gaps).
– “Stagger timetable”: on Saturday AM local time – avoids SOC staffing.
– Drops snippingtool copy signed with stolen Globacom MS cert to evade digital-signature inspection.

• Broader Impact
– 2023-11 wave hit Japanese medical firms → 240 TB exfiltrated (HIPAA fines projected > $4 M).
– Affiliates observed co-existing with LockBit deployment on same networks – “double extortion ladder” strategy.

• IOCs: GitHub.com/search?q=biglock-ioc-2024
• Scriptable removal PS1: https://github.com/ChristopherTD/PS-BigLockKiller/releases
• FBI FLASH alert #MU-000142-TT (Nov 2023) – request for incident logs.

Share & Stay Safe – Report new samples to ID-Ransomware or upload to VT to help tracking.