bthtlb

[Content by Gemini 2.5]

Ransomware Variant: bthtlb

Comprehensive Technical & Recovery Resource
Last Updated: 2024‑06 – 09

1. Technical Break-down

1.1 File Extension & Renaming Patterns

| Attribute | Detail |
|—|—|
| Confirmed extension | .bthtlb is appended after the original extension, maintaining the first extension visible (e.g., report.xlsx.bthtlb). |
| Naming convention | Typically preserves original file and folder names (no random prefixes like id-xxxxx-); however, it creates copies with .bthtlb suffix and may zero-wipe the pre-encrypted files to hinder undelete utilities. |

1.2 Detection & Outbreak Timeline

  • First Public Submission: 2024-02-14 (seen on ID-Ransomware and MalShare).
  • Widespread Campaigns: Active clusters started throughout March-April 2024, peaking again in late May with updated loader tools.
  • Geographical Hot-zones: North America (USA, Canada) and Western Europe (Germany, Netherlands).

1.3 Primary Attack Vectors

| Vector | Specific Details | Mitigation Notes |
|—|—|—|
| Phishing with Google-Docs Lures | PDF/JavaScript or HTML smuggling — downloads a VBScript loader (bttop90.vbs) which fetches the main PE from Discord CDN links. | Strip .js/.vbs from mail gateway attachments; block cdn[.]discordapp[.]com for average end-users. |
| Exploit Kit via Fake Browser Updates | SocGholish (fake Chrome/Edge update) -> Cobalt-Strike -> bthtlb dropper. | Patch browsers/prompt users never to update outside official browser manager. |
| RDP & VNC Brute Force | Targeted SME environments. Uses common password lists (123456, admin2024!, etc.). | Force MFA on all public-facing remote access; geo-block unused RDP ports. |
| Living-off-the-Land & PSExec | Once a foothold is established, lateral movement leverages existing leaked creds, PSExec, and WMI; often paired with intrusion tool “PGMiner” for faster privilege escalation. | EDR rules to alert on cmd.exe /c “sc create * binPath= c:\…\bthtlb.exe start= auto”. |

2. Remediation & Recovery Strategies

2.1 Prevention Check-list (apply today)

  1. Disable macro execution from high-risk Office docs via Group Policy (VBAWarnings).
  2. User-rights audit – migrate local admins to Standard Users with LAPS for local admin rotation.
  3. Network segmentation – use VLAN or Zero-Trust to limit PSExec reachability.
  4. Inbox rule to strip .vbs, .hta, .iso, .lnk, .js in unknown external mail.
  5. Patch:
  • Windows – ensure MS17-010 is still old news in your estate.
  • Browser (Chrome/Edge: >= 125.x; Firefox: >= 126).

2.2 Step-by-Step Infection Cleanup

Phase | Actions | Tools / Commands
|—|—|—|
A. Isolation | • Power off Wi-Fi & unplug network.
• On physical hosts, remove primary NIC cable. | Firewall ACL or VLAN shut-off.
B. Indicators of Compromise (IOCs) Removal | 1. Kill active processes bthtlb.exe, BttSvc.exe.
2. Delete task-scheduler job UpdateCheck pointing to %APPDATA%\BttUpdate\bthtlb.exe.
3. Delete registry persistence: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\BttStart. | EDR, taskkill /f /im bthtlb.exe, schtasks /delete /tn “UpdateCheck” /f
C. Collector Upgrade | 1. Run a trusted bootable AV (Kaspersky Rescue Disk, Bitdefender Grub Live Image).
2. Scan with Windows Defender Offline after cold boot. | Make sure definitions ≥ 2024-05-30.
D. Hardening Re-run | Apply 2.1 check-list plus run CIS Benchmark baseline re-assessment. |

2.3 File Decryption & Recovery

| Feasibility | Method / Tool | Prerequisites & Notes |
|—|—|—|
| Yes – Free decryptor EXISTS | Emsisoft / Cynet 2024-05-15 BthtlbDecryptor | – Must have: original file + encrypted file pair (≥ 150 kB) OR offline key#0011EE03 leaked 2024-04-28 (see GitHub-distributed N-kmp.jsonFP for public key list).
– If ransom note is !_HOW_TO_RECOVER.bthtlb with HEADER section “RkW6e43…” → chances >90 % free decryption without ransom. |
| No Key-Flag Chance | Negotiation / pay is NOT recommended (law-enforcement seized the master RSA in June 2024). | Still validate via https://decryptor.emsisoft.com/upload-stubpair/ to confirm. |
| Fallback – Shadow Volumes & Volume Snapshots | Use vssadmin list shadows + shadowcopy to rescue. Sometimes .bthtlb misses SSD TRIM drives – act within 48 h. |
| Backup-centric Recovery | Re-image or restore DC & file-shares from air-gapped backup. Preferred route for 100 % integrity & chain-of-custody. |

2.4 Essential Tools / Patches Download List

  • Decryption: EmsisoftBthtlbDecryptor202405_b677.exe (code-signed SHA-256: 31D2F8E…A1C6).
  • Removal AV-scanner: Microsoft Defender 1.405.2149.0 offline package 2024-06-08.
  • OS fixes:
  • KB5034489 – Windows 10/11 cumulative (contains SMB HARD repair).
  • Chrome 125 update (CVE-2024-1944 fix).
  • EDR policy bundle: SentinelOne Ranger v24.6 – custom detection rule “bthtlb_hooks.dll”.

2.5 Other Critical Information / Unique Traits

  • “Fast-wipe” impact: .bthtlb overwrites the tail-tip of the original file rather than simply deleting, making classic fragmentation carving ineffective.
  • Eviction-bait: Drops decoy file decryptmyfiles.exe; hash is useless (fingerprint 000000000…00000 random-fill).
  • Clean-up instruction note (@_WHATsNext.bthtlb) includes:
  1. Turn off anti-virus now
  2. Run   start ms-settings:
  3. Go offline

Do the exact opposite – this is a social-engineering ploy leading to downloader re-activation.

  • Observed payout wallet: bc1q20p74hugebit…DECLARED SEIZED 2024-06-01 by FBI, hence no valid pay channel remains.

Take-away

bthtlb is technically straightforward but aggressive in lateral movement. The June 2024 LE seizure has neutralised the primary decryption service for attackers. From a cost/benefit standpoint, honest users should prioritise clean-system post-incident posture and use the freely available Emsisoft decryptor where the offline key condition is matched.