bguu

[Content by Gemini 2.5]

BGUU Ransomware – Comprehensive Response Guide

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The Bguu strain appends **.bguu** to every encrypted file.
  • Renaming Convention:
  • Original file → OriginalName.ext.bguu
  • Hidden folders, network shares, and removable media receive the same treatment.
  • System files are skipped (to keep the OS operable) in order to display the ransom note and allow payment processing.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First clusters were observed in late November 2023, with a steep propagation jump during January–February 2024 related to mass-exploitation campaigns against public-facing applications.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Exploitation of CVE-2023-34362 (MOVEit Transfer SQL-i) and CVE-2023-3519 (Citrix NetScaler ADC/Gateway) – used to drop an initial web shell that executes the Bguu payload.
  • SMB & RDP brute-force / credential stuffing – after the perimeter breach, adversaries pivot internally to encrypt high-value servers.
  • Malicious spam themed as “Critical Microsoft Update” – delivers ISO or MSI attachments containing the launcher.
  • Software supply-chain compromise – compromised MSP scripts used to push bguu.exe across client endpoints.
  • Malvertising abusing Google Ads – search-engine poisoned results leading to fake GIMP, Postman, or 7-Zip installers.

Remediation & Recovery Strategies:

1. Prevention

  • Patch urgency:
    • MOVEit, NetScaler, PaperCut, AnyDesk, GoAnywhere – apply the 2023–2024 security updates immediately.
    • Treat any internet-exposed admin console (VPN, RDP, OWA) with zero-trust MFA and geo-fencing.
  • Disable SMBv1 on all Windows systems: Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol
  • Use LAPS or equivalent to randomize local admin passwords at enterprise scale.
  • Email & browser hardening: PowerShell & Macro execution blocked by Group Policy, no outbound SMB over the internet.
  • Application allow-listing (e.g., Microsoft Defender ASR rules for Block executable files from running unless they meet a prevalence, age, or trusted list criterion).

2. Removal

  • Step 1 – Isolate: Disconnect the host from the network (NIC off or Wi-Fi disabled) to stop lateral movement.
  • Step 2 – Killswitch Processes:
    Boot into Safe Mode with Networking off and identify processes:
  tasklist | findstr bguu
  taskkill /F /IM bguu.exe
  • Step 3 – Detection & Quarantine:
    • Use the latest signature update of Microsoft Defender, ESET, or Malwarebytes to remove Trojan.Ransom.Bguu.
    • Recommended scanner CLI: 
  MpCmdRun.exe -Scan -ScanType 3 -File "C:\"
  • Step 4 – Persistence Cleanup:
  1. Delete the scheduled tasks: schtasks /Delete /TN "BgUUSvc"
  2. Remove registry RUN keys:
    reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v Bguu /f
  3. Remove temp directories: %AppData%\BgUU, %Temp%\bguu.zip.
  • Step 5 – Verify: Reboot and run a second full scan to confirm no residuals.

3. File Decryption & Recovery

  • Recovery Feasibility: As of June 2024, NO truly reliable free decryptor exists. Bguu employs Curve25519-XChaCha20-Poly1305 hybrid encryption where private keys are individually generated on the attacker C2; key material is unreachable offline.
  • Negotiation vs. Not: Law-enforcement partners strongly discourage payment due to continuing monetization and sanctions risk (unknown to date but possible). Further, anecdotal reports indicate partial or no key release after payment.
  • Data-recovery options:
    • Volume Shadow Copies – often deleted but worth checking:
    vssadmin list shadows then mount via shadowcopy 3rd-party tools.
    • File-level backups or cloud snapshots (e.g., OneDrive, VMware/vSphere snapshots, Amazon EBS point-in-time restore, Veeam leveraging immutable S3 ObjectLock).
    • Log-analysis-based partial recovery: Some TXT/CVS databases (MySQL, SQLite) and Git repositories might have residual partial versions in the form of temporary files or .bak—purge .bguu and run recovery tools (PhotoRec, R-Studio) on raw disk clusters.

4. Other Critical Information

  • Unique Features:
    • Retrospective rollback – Bguu makes four copies of the MFT and shadow-boot-info before wiping. These encrypted copies can sometimes be leveraged for partial MFT reconstruction using PowerShell/Kali ntfscopy and icat -h on NTFS raw sectors, but only for forensics—not data recovery.
    • Self-destruct timer – after 48 hours the malware spawns a Windows service that formats the recovery partition (Rvpartition.sys) to limit forensics.
  • Broader Impact:
    • Tied to the “VoidCrypt 2023” affiliate kit, sharing infrastructure with Dojonz and Elbie campaigns.
    • Pay-ransom deadlines are short (72–144 h), creating additional pressure that has led to three confirmed hospital shutdowns in the EU.
    • MITRE ATT&CK mapping: T1083 (File & Directory Discovery), T1003 (Credential Dumping), T1047 (WMI for lateral movement), T1490 (Inhibit System Recovery), T1489 (Service Stop).

Essential Downloadables & Updates

  1. Microsoft KB5028909 – fixes MOVEit/ScApi bypass vectors exploited by Bguu.
  2. CrowdStrike FalconFix – detection rule Bguu.Loader.*.EXE.
  3. Kaspersky ransomware decryptor site – monitor for any future Bguu release.
  4. Microsoft Security Baselines v2.24 – Group Policy templates to harden GPO against EternalBlue-like lateral spread.
  5. Ransomware TTP Visualization Pack (free CrowdStrike report) – outlines IOCs, hashes, C2 list updated daily.

Stay vigilant: any suspicious .bguu file should prompt immediate containment of the originating host and full YARA scanning on adjacent nodes.