bitenc

[Content by Gemini 2.5]

Ransomware Profile – .bitenc (“MedusaLocker / Bitenc variant”)

Technical Breakdown

1. File Extension & Renaming Patterns

  • File extension used by Bitenc: every encrypted file APPENDS the suffix “.bitenc”.
    Example: Quarterly_Report.xlsx → Quarterly_Report.xlsx.bitenc
  • Renaming convention: no leading prefix, no e-mail addresses, no random hex strings. The ransomware simply appends “.bitenc”, leaving the original filename otherwise intact.

2. Detection & Outbreak Timeline

  • First public sightings: late-November 2019, clustering heavily in early 2020 (December 2019 – February 2020 waves).
  • Peak period: January 2020 (numerous healthcare & SMB incidents).
  • The Bitenc strain is a dedicated sub-build of MedusaLocker promoted on dark-web RaaS portals during that timeframe.

3. Primary Attack Vectors

  • Exploitation of internet-exposed RDP (TCP/3389)
    – Brute-force, credential stuffing, or previously-purchased RDP-access listings.
  • Phishing e-mails containing malicious macro attachments (.docm, .xlsm) or ISO/IMG containers that download the initial loader.
  • Living-off-the-land lateral movement & deployment
    – Uses PowerShell Empire, WMI, PSExec, or Cobalt Strike beacon to stage Bitenc to multiple machines.
  • Vulnerability exploitation that was not a major propagator for Bitenc itself (the actor’s tendency was RDP first), but blue-teams should still patch: EternalBlue (MS17-010), BlueKeep (CVE-2019-0708), and CVE-2019-19781 (Citrix ADC).

Remediation & Recovery Strategies

1. Prevention

  1. Close or restrict RDP to VPN-only; enforce NLA, 2FA, and strong password policy.
  2. Apply 2019–2020 patches (especially MS17-010, CVE-2019-0708, and edge-CVEs above).
  3. Disable Office macro auto-run; train staff against email lures.
  4. Segment networks and restrict lateral admin tools (PSExec, WMI, PowerShell remoting) via GPO.
  5. Maintain offline / immutable backups (3-2-1 rule).
  6. Deploy EDR/NG-AV rules looking for “MedusaLocker” YARA or BITLOCK hash patterns.

2. Removal (step-by-step)

  1. Disconnect the infected host from the network (both LAN & Wi-Fi).
  2. Identify active malware hives:
    – Check unusual Scheduled-Tasks (MicrosoftUpdateX, or randomly-named tasks executing .exe under %APPDATA%)
    – Review Autoruns and Registry Run keys for "C:\Users\<user>\AppData\roaming\svhost.exe" or variants.
  3. Boot into Safe-Mode with Networking (Windows), then run legitimate AV/EDR (use Malwarebytes, Windows Defender Offline, or Bitdefender Rescue CD). Delete:
    – Executable %APPDATA%\svhost.exe (usual name)
    – Scheduled task / registry keys
  4. Verify persistence: run autoruns64.exe (Sysinternals) and eliminate what differs from a clean gold image.
  5. Wipe shadow copies and free space can sometimes be skipped after scanning – Bitenc already deleted VSS via vssadmin Delete Shadows /All /Quiet, but Image-Level backups (Veeam, Acronis) may still exist.

3. File Decryption & Recovery

  • Recovery feasibility: No free decryption tool exists for Bitenc. It uses AES-256 for bulk-volume encryption with RSA-2048 to protect the session key — only the attackers’ private key can recover files.
  • Your options:
    – Restore from offline backups.
    – Locate persistent volume-shadow copies (check with Shadow Explorer or vssadmin list shadows /for=C:).
    – Leverage “Windows File History”, Veeam CBT snapshots, or SAN snapshots that were air-gapped.
  • Crucial patches: The ransomware itself does not require a patch to restore, but patching core OS and disabling RDP will prevent re-infection.

4. Other Critical Information

  • Unique characteristics:
    – Post-encryption it drops a ransom note titled “HOWTORECOVER_FILES.html” in every encrypted folder.
    – Creates a scheduled task named “Mshta.exe” running every 15 min to relaunch the ransom note.
    – Sets a red wallpaper with the message “YOUR PERSONAL ID: ” in BMP format overwritten at C:\Users\Public\Pictures\desktop.jpg.
  • Broader impact: Bitenc disproportionately hit healthcare organizations during the early 2020 COVID-19 surge, causing elective-surgery cancellations and delaying lab services in Europe and North America. Subsequent indicators (source code overlap) suggest the operator used it as a “bridge campaign” before moving to newer MedusaLocker forks.

Stay observant: new RaaS affiliates continually re-brand the same codebase under different extensions.