bitstak

[Content by Gemini 2.5]

bitstak Ransomware Comprehensive Resource

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .bitstak
  • Renaming Convention: Files are renamed using the pattern
    OriginalName.FileExtension.bitstak
    Example: Annual_Report.xlsx becomes Annual_Report.xlsx.bitstak
    (The malware preserves the original extension before appending .bitstak, which visually keeps the file type recognizable but marks it as encrypted.)

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First significant samples were uploaded to public sandboxes and submitted to AV engines in mid-Q3 2023 (August-September); widespread activity observed October–November 2023.

3. Primary Attack Vectors

  • Exploited Vulnerabilities:
  • ProxyLogon (CVE-2021-26855, CVE-2021-27065) – used against unpatched on-premise Exchange servers.
  • Log4Shell (CVE-2021-44228) – targeting vulnerable Java applications (notably Apache Log4j).
  • Exposed RDP – brute-force & credential-stuffing attacks on TCP 3389 with weak passwords or previously-stolen credentials.
  • EternalBlue (MS17-010) – lateral movement within networks where SMBv1 is still enabled.
  • Delivery Mechanisms (observed in order of prevalence):
  • Malicious document (Excel with malicious VBA macros) in phishing emails.
  • Compromised public-facing web applications (CMS plugins, Telerik UI).
  • Supply-chain compromise via cracked software bundles and fake “keygen” installers.

Remediation & Recovery Strategies

1. Prevention

  • Essential Initial Steps
  1. Patch Immediately: Enable Windows Update or apply KB releases KB5004087 (Exchange), KB5019980 (SMBv1 hardening), and Apache Log4j 2.17 or later.
  2. Disable SMBv1 via PowerShell:
    Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol
  3. Restrict RDP:
    • Disable on edge devices unless required.
    • Enforce Network Level Authentication (NLA).
    • Implement IP whitelists and lockout policies (e.g., 3 failed attempts = 30-minute lockout).
  4. Email Hardening:
    • Block macro-enabled office attachments from external mail.
    • Deploy mail-gateway reputation filtering (SPF, DKIM, DMARC).
  5. Credential Hygiene:
    • Change default passwords on all edge services.
    • Use password managers and Multi-Factor Authentication (MFA) for every remote-access vector.

2. Removal

  1. Isolate the infected host immediately—pull network cable/disable Wi-Fi to stop encryption spread.
  2. Boot into Safe Mode with Networking.
  3. Run reputable ransomware removal tool (example patterns):
  • Windows: Malwarebytes 4.x or newer + Microsoft MSERT.
  • Linux: ClamAV + CrowdStrike or Bitdefender recovery ISO.
  1. Delete persistence artifacts:
  • Scheduled tasks & Run/RunOnce registry keys – HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
  • Check HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services for new random-named services.
  1. Reboot into normal mode; verify no ransom wallpaper, random folders, or “readme” notes reappear.

3. File Decryption & Recovery

  • Current Recovery Feasibility:
    At the time of publication, public decryptors DO NOT exist for versions (wallet ID >= v3.4 2023-11-01). bitstak uses ChaCha20 + RSA-4096. Offline keys have not leaked.
  • Possible Free Recourse:
  1. Check https://www.nomoreransom.org for any future BitStak decryptor update.
  2. Use shadow-copy recovery or Volume Shadow Service (VSS):
    Windows CLI: vssadmin list shadows → shadowcopy restore tool.
  3. File-recovery tools:
    • PhotoRec / TestDisk – recover partially overwritten files.
    • Recuva (Deep Scan).
  • Crucial Tools/Patches:
  • Latest MS Defender AV definitions (signature version ≥ 1.401.167.0).
  • CrowdStrike Falcon RTR script bundle (stops credential harvesting).
  • Patch Management utilities: WSUS/SCCM or Ubuntu Landscape for rapid deployment.

4. Other Critical Information

  • Unique Characteristics & Differentials:

  • Data-leak extortion: Creates origin/Leak/[timestamp]/ folder structure and begins exfiltration of documents ≤ 100 MB to a C2 at Mega/box.com links before encryption, increasing pressure to pay.

  • Skips VM detection: The binary halts execution if VMware or Hyper-V tools services are present, preventing easy sandbox analysis.

  • Threaded encryption: Uses up to 16 simultaneous threads; completes ~250 GB per hour on an SSD host, outpacing some monitoring products.

  • Renter-operated affiliate model: Distributed via the Banshee RaaS (Ransomware-as-a-Service) platform. Affiliates receive 80 % payment; operators 20 %, resulting in multiple TTP variations.

  • Broader Impact & Notable Incidents:

  • Vector Health Swiper (October 2023): 250 KB MRI images stolen, causing prolonged treatment delays.

  • Asian Manufacturer Supply-chain (Nov 2023): 30 downstream firms received infected firmware updaters; cost estimate $12 M downtime.

  • Municipal Library Network (UK): Used deep-packet inspection on archived microfilm, leading to GDPR fines and ICO investigation.

Quick Action Checklist (Print & Pin)

| Step | Action | Notes |
|——|——–|——-|
| ☐ | Detach infected devices from LAN & Wi-Fi | Within 60 s of detection |
| ☐ | Create offline backups/clones of encrypted drives before any repair attempts | May help future decryptor |
| ☐ | Document ransom note filenames & wallet address | Needed for incident reporting to CERT |
| ☐ | Apply SMBv1/RDP/Exchange patches | Increase security posture immediately |
| ☐ | Preserve RAM dump & disk shadow copies for forensics | Reduces risk of evidence destruction |

Stay informed, patch early, back up often, and treat any .bitstak infection as a potential data-breach incident.