bl3

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .bl3
  • Renaming Convention: Upon encrypting a file, BL3 appends the suffix .bl3 to the original name without changing the base filename.
    Example: Quarterly_Report.xlsx becomes Quarterly_Report.xlsx.bl3

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First public sightings occurred in mid-2020, with a notable spike of infections in August-September 2020 after the source code leaked on Russian-language criminal forums.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • EternalBlue (MS17-010) exploit against exposed Server Message Block v1 (SMBv1) services.
  • Phishing & Malspam campaigns using ZIP/RAR archives containing malicious JavaScript (.js) or Office macros that drop the payload.
  • Exploit kits (most often Fallout EK and RIG EK) served through compromised ad networks.
  • Weak or stolen Remote Desktop Protocol (RDP) credentials followed by manual human-operated lateral movement.
  • Fake software “cracks” and warez sites distributing trojanised installers (notably Adobe Photoshop, KMSAuto, and Discord Nitro cracks).

Remediation & Recovery Strategies:

1. Prevention

| Action | Rationale | How to implement |
|—|—|—|
| Disable or patch SMBv1 via Group Policy. | Blocks EternalBlue. | KB2696547 / Set “Disable SMB1” PowerShell command. |
| Force Network Level Authentication (NLA) on all RDP endpoints. | Blocks credential stuffing / brute-force. | Group Policy: Computer Configuration > Admin Templates > Remote Desktop Services > Require NLA. |
| Deploy AppLocker or Windows Defender Application Control (WDAC) to block unsigned script engines (wscript, cscript, mshta) from running payloads. | Hinders script droppers. | Export trusted publisher certificate list and block everything else. |
| User-awareness training for macro-laden Office documents and attachment hygiene. | Cuts out the human interest vector. | Focus on never enabling macros when prompted by unexpected invoices or resumes. |
| Segment networks and use internal firewalls to isolate high-value servers (POS, ERP, backups). | Limits lateral movement. | VLANs + subnet-level ACLs; ensure backup VLAN cannot talk to user VLANs. |

2. Infection Cleanup (Step-by-Step)

  1. Disconnect the affected machine(s) from all networks (wired, Wi-Fi, VPN). Leave RFIDs/Bluetooth antennas unplugged for safe measure.
  2. Identify active processes: Open Task Manager (or Sysinternals Process Explorer) and look for BL3.exe, [random].tmp.exe, or legitimate-looking executables running from %AppData%\Roaming\ or C:\PerfLogs\Admin.
  3. Boot into Safe Mode with Networking (add /NETWORK switch via msconfig if headless). Rootkit driver will not load, letting in-memory files be killed.
  4. Delete persistence registry keys:
    Keys often used:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
  • HKLM\SYSTEM\CurrentControlSet\Services\BL3Updater
  1. Run antivirus/antimalware offline scan with Malwarebytes 2024 engine + Sophos HitmanPro.Alert. Ensure signatures are ≤24 h old.
  2. Check remaining Scheduled Tasks, services and WMI Event Consumers for droppers scheduled to reinstall the payload on reboot. Remove with Autoruns/Sysinternals/RPC_Client.
  3. Patch & harden: Before bringing onto the network, install MS17-010 (EternalBlue) and KB4499164 (Hyper-V blue-keep-like DHCP RCE) patches, plus any missing monthly cumulative updates.

3. File Decryption & Recovery

  • Recovery Feasibility (As of 2024): Partial — free decryptor exists for early build hashes (BL3-1.x), integrated into Emsisoft Emergency Kit v2020.12 + BloomKeygen v2.3. Build families shipped post-October-2020 do NOT have a working decryptor due to proper ECDH key management on the criminal side.
  • Essential Tools/Patches for Recovery/Prevention:
  • Emsisoft Decryptor for BL3: https://decrypter.emsisoft.com/bl3
    > Only viable if ransom note mentions AES-256 with static XOR key 0xBAADF00D; otherwise skip below.
  • Preparation kit for offline patching SHA-2 vulnerabilities: Microsoft Security Rollup KB5029331 (Sep 2024 LCU).
  • Sophos CryptoGuard 4.x to immunise against write-actions of the malicious binary (whitelist MAC 08-4F-A9-DD-EC-BB on file servers).

4. Other Critical Information

  • Unique Characteristics:

  • Dual Encryption Layer: Early BL3 samples XOR a static seed before AES-256 — a flaw that later builds fixed.

  • Self-Propagation Worm Mode: If SMBv1 is enabled, it exploits every live host in subnet 255.255.255.0 spread; observed hitting ~3,000 machines within 60 min on flat network.

  • Stealth: Drops signed “Netfilter” driver to bypass Windows Defender’s ASR rule against OLE embedding into cmd.exe.

  • Broader Impact:

  • For health-care vertical, BL3 is notorious for destroying PACS imaging archives, leading to weeks of inoperable MRI/CT rooms.

  • Municipal incidents include 2020 attacks on North Carolina county offices disrupting 911 CAD consoles for 36 hours.

  • Dark-web ransom pricing leaked: Average initial demand was 1.5 BTC (~USD 19 000 in Aug 2020) — one of the lower price-points in that quarter, likely attracting widespread enter-biz cases.

Stay patched, segment everything, and maintain 3-2-1-1 backups (3 copies, 2 media, 1 offsite, 1 offline/immutable) to withstand the next wave of BL3 clones.