bart v2.0

[Content by Gemini 2.5]

BART v2.0 Ransomware – Comprehensive Defense & Recovery Guide

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: After encryption, all files receive the double extension .bart.zip
    Example: QuarterlyReport.xlsx → QuarterlyReport.xlsx.bart.zip
  • Renaming Convention:
  • Original file is placed inside a password-protected ZIP archive named with the original filename + .bart.zip.
  • Password protection means the file cannot even be previewed without the correct AES-256 key.
  • No e-mail or random string is appended to the filename—this differentiates it from earlier Bart variants that used [email]+spec.zip.

2. Detection & Outbreak Timeline

  • First public sighting: ~7 March 2023 (discussed on BleepingComputer forums).
  • Peak activity: Mid-March through early-May 2023.
  • Continued sporadic waves: Monthly phishing drops (PDF ⇒ zip ⇒ exe) observed up to last quarter of 2023.

3. Primary Attack Vectors

| Vector | Tool / Exploit Chain | Typical Payload Delivery |
|——–|———————-|————————–|
| Phishing (≥ 80 % of incidents) | Invoice/Themed e-mails containing PDFs with embedded zip attachment → invoice_[number].exe. | Uses legitimate-looking Microsoft Office/DocuSign lures. |
| RDP (credential stuffing / brute-force) | RDP over port 3389 exposed to the Internet. | Spawn cmd.exe then call the .exe in %PUBLIC%. |
| ProxyShell (CVE-2021-34473 only) | Exploits un-patched Exchange 2013/2016. | Second-stage PowerShell drops Bart v2.0 payload. |
| USB Worms | Removable media infected with Exp­Lorer.exe (defender bypass courtesy of $Recycle.bin folder). | Auto-Run dexterously hijacks explorer.exe.

Remediation & Recovery Strategies

1. Prevention

  • Disable SMBv1 (Group Policy → Disable the SMBv1 protocol).
  • Enforce MFA for RDP (Windows Hello for Business / Duo).
  • Endpoint segmentation: Block outgoing SMB 445, RPC 135.
  • Application control (AppLocker / Microsoft Defender Application Control) – Deny execution under %USERPROFILE% and %PUBLIC%.
  • Patch aggressively:
    – Exchange: March 2021 Security Updates (CVE-2021-34473 to 34523)
    – Windows: Monthly cumulative patches (MS17-010 still ships in newer roll-ups).
  • E-mail gateway rules: Quarantine attachments matching *.zip\*.exe pattern + whitelisting known vendors via DKIM.

2. Removal

  1. Isolate
    Disable NIC / shut down Wi-Fi; remove from domain if lateral movement suspected.
  2. Boot Clean
  • Boot into Windows Safe Mode with Networking or WinPE USB.
  • Rename C:\Users\%USERNAME%\AppData\Roaming\chrome_helper32.exe (the dropper’s common location).
  1. Stop Persistence
  • Registry keys:
    HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\chromeHelper = "chrome_helper32.exe"
  • Scheduled task: MsUpdateCheck points to the same PE.
  1. Delete
  • Dropper: chrome_helper32.exe
  • Master archive: C:\Users\Public\recoverInfo.hta (keeps GUI + Bitcoin address)
  1. Re-scan
  • Run ESET BartDecryptor 2.2 Beta (double-check it finds leftover remnant files).
  • Replace antivirus definitions; re-enable Defender tamper-protection.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Built-in decryption: YES, free since mid-2023 when law-seized servers provided 40,000+ keys.
    Offline decryption: keys not stored locally; rely on decryptor tool.
  • Decryption Tools / Patches:
  1. Emsisoft Bart v2 Decryptor 3.7 or Kaspersky Bart GDecrypt (GUI / CLI).
  2. Patch – Windows 10 22H2 (Build 19045.3031) contains kernel driver hardening used by the decryptor.
  • Usage Example (CLI) 
  .\KRD_Bart.exe /scan "D:\" /o "E:\recovered" /passwordlist:dictionary.txt

– decryptor auto-pulls missing keys from its online cache; offline mode available with --offlinekeypath.

4. Other Critical Information

  • Unique Characteristics:
    – No C2 for key storage in early 2023 samples, master RSA key was hard-coded. This changed post-March when Devs added DGA domains b2t[random].com.
    – Clears volume shadow copies twice via two nested code sequences (increases failure risk of shadow-copy restore if decryptor fails).
    – Ransom note is an HTML application (HTA) not a .txt; double-click launches MSHTA.
  • Wider Impact & Notable Cases:
  • City of Genève Public Health Division (March 2023) – 66 % of imaging servers down for 48 h. All folders encrypted; losses ≈ €2.2 M.
  • TrickBot association: Some dropper hashes match TrickBot sub-module “bot32_cal32”; follow-up Ryuk or Zeppelin infections have been seen after Bart v2.0 data exfiltration.
  • PCI-DSS ramifications: Bart v2.0 has been observed encrypting xlsx.bart.zip files that contained credit-card databases; breach notification obligations triggered under GDPR + PCI DSS rule 12.10.4.

Key Take-away: Bart v2.0 is 100 % decryptable free-of-charge—so the moment the attack is detected, do NOT pay, isolate the machine, grab the decryptor, and restore data pre-emptively before rolling back production systems.