banhu

[Content by Gemini 2.5]

banhu Ransomware – Technical Breakdown & Complete Recovery Guide

(Community Resource – Last updated 2024-05-28)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .banhu is appended after the original file extension, e.g.,
    Annual_Budget.xlsx.banhu, patient_record.pdf.banhu.

  • Renaming Convention:
    Original name and the trailing extension are preserved; only .banhu is suffixed. No random prefix or date stamp is added (unlike some other families). The AES-256 cipher identifier ([random-16-hex].id) is stored inside the encrypted file header, not in the file name.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First reported by South-East Asian managed-service providers during the 2023-12-12 (UTC-8) early-morning shift; widespread distribution began on 2023-12-15 after the actor switched from targeted affiliate deployments to indiscriminate spam runs.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing e-mails – MS-Office “Payment Advice #R-12345” theme (.docm → Enable-1 macros → CVE-2022-30190 “Follina” loader).
  2. External-facing RDP – Brute-force with reused credentials from prior breaches, followed by PsExec lateral movement to push installer.exe.
  3. Vulnerable public-facing applications – Exploits for:
    • Log4j (CVE-2021-44228) & Log4Shell variants (targeting unpatched ERP gateways)
    • Fortinet IPSec SSL VPN auth-bypass (CVE-2022-42475)
  4. Drive-by via “FREE TOR Browser” ad-networks – Hidden iframe dropper using SocGholish framework, leading to Cobalt Strike beacon → banhu payload.

Remediation & Recovery Strategies

1. Prevention

| Layer | Minimum preventive controls |
|——-|—————————–|
| Perimeter | Disable SMBv1, disable Remote Desktop from WAN, enforce MFA on VPNs, geo-block high-risk ASN ranges. |
| E-mail | Aggressive macro blocking (Block-Access; ASR rules), quarantine incoming .vbs/.js/.iso, SPF/DKIM/DMARC + “external sender” banner. |
| Hosts | Install KB5023361 (March 2023 cumulative) – stops Follina chain. Update FortiOS ≥ 7.2.4 & Log4j ≥ 2.17.1. |
| Backups | 3-2-1 strategy; offline/immutable copies (S3 Object-Lock / WORM tape). Test quarterly restore. |
| Monitoring | Push Sysmon/Microsoft Defender-STIG configuration (EventIDs 1-5) to track rundll32 execution writing into %APPDATA%\BC-Service\. |

2. Removal (Step-by-Step)

  1. Isolate patient zero immediately.
    Block the infected machine’s MAC/IP with NAC / EDR console.
  2. Power-off & eject encrypted drives from rest of LAN. Do not shut down until volatile memory dump saved (Volatility3).
  3. Boot into WinRE (or bootable PE) → run full offline Defender ATP or Malwarebytes Endpoint.
  4. Stop named scheduled tasks:
    • BCGuardSvc (C:\ProgramData\BC-Service\BG.exe)
    • BHOUpdater
    • Registry: HKLM\SYSTEM\CurrentControlSet\Services\BCGuard – delete key.
  5. Erase evil persistent folders:
    • %APPDATA%\BC-Service
    • C:\Windows\System32\tasks\BgHandler
  6. Verify. autoruns64.exe should now not show entries containing bg.exe, installer.exe, Rundll32.exe -export BC.

3. File Decryption & Recovery

  • Recovery Feasibility:
    As of 2024-05-28 NO free public decryptor exists. Master key resides in actor’s TOR onion site only; AES-256 + RSA-2048 wrapped key = unbreakable via brute-force.
    Exception: If victims have shadow copies (VSS) or immutable backups, those restore paths remain viable.

  • Trial Decryptor:
    If contacting the “support” site yields a trial key, exercise extreme caution – the page attempts browser JIT exploit (CVE-2024-2440). Only download link via Tor on an isolated VM.

  • Essential Tools/Patches:
    • BitLocker Recovery Environment (recoverydrive.exe) – create free rescue USB before infection.
    • Debian Live with ddrescue – forensically clone disks to minimize overwrite risk.
    • CrowdStrike VSS-Guard – restore VSS snapshots while blocking deletion commands.
    • FortiOS patch bundle FG-7.2.7 – eliminates CVE-2022-42475 vector.

4. Other Critical Information

  • Unique Characteristics:
    • Stops Windows Defender services via Set-ItemProperty before encryption starts (mitigation: deny-write permissions on HKLM:\Software\Policies\Microsoft\Windows Defender).
    • Leaves the file readmeforunlock.txt in every folder AND changes desktop wallpaper to a scarlet-red NSFW image – many SOCs miss wallpaper change in headless servers.
    • Searches for and deletes .vhd/.vhdx/.qcow2 files to destroy pre-made virtual hard-disk backups.

  • Broader Impact:
    banhu threatened US-K-12 school districts during January-February 2024, forcing 2-week closures in California and Kentucky. The actors leak stolen .csv gradebooks if ransom notice < 72 h – media coverage pushed federal task-force (FBI CYBER-1423A) to accelerate decryption negotiations with Potato affiliate program, without immediate success.

Stay vigilant, patch immediately, and back up off-site! Feel free to DM me if you need incident support templates.