cmdransomware

[Content by Gemini 2.5]

Technical Breakdown – cmdransomware (alias: “CMD Ransomware”, “Nitro CMD”)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cmdransomware – the malicious binary appends this literal string as a secondary extension to every encrypted file.
  • Example transformation:
    Quarterly_Report.xlsx → Quarterly_Report.xlsx.cmdransomware
  • Renaming Convention:
  • Victim files keep their original name; no obfuscation, prefixes, or random IDs are used.
  • Each encrypted file is immutable once the payload completes, so double-encryption or duplicate renaming anomalies have not been observed in-the-wild.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First publicly documented samples appeared late March 2022 on dark-web marketplaces and English-language criminal forums.
  • Wider circulation was noted during April–June 2022 when an affiliate campaign systematically targeted healthcare and public-sector networks worldwide.

3. Primary Attack Vectors

  • Windows SMBv1 vulnerability chain – leverages lateral-movement scripts that piggyback on un-patched EternalBlue (MS17-010) code.
  • RDP brute-force & credential-spray payloads – specifically MSSQL LDAP enumeration that extracts known passwords reused from previous breaches.
  • Phishing emails bearing ISO image attachments – ISO drops a PowerShell stager (schedule.cmd) disguised as an OCR invoice script.
  • Software supply-chain abuse – observed hijacked install packages for popular utilities (e.g., Notepad++ plugins, Git GUI update spoofing) signed with revoked code-signing certificates (DV, StartCom CA).
  • Command & Control (C2) relies on TOR hidden-services, inbound traffic wrapped in Base64-over-DNS TXT queries.

Remediation & Recovery Strategies

1. Prevention

  • Immediately disable SMBv1 via Group Policy:
    Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol.
  • Require MFA on every exposed RDP instance. Prefer VPN tunnels or Azure Bastion solutions where practical.
  • Block ISO file receipt except via specific allow-list (G-PO attachment filter).
  • Update Microsoft Defender signatures (KB5013700+) and enable Network Protection. CMDransomware is now detected by template Ransom:Win32/Cmdr.
  • Harden PowerShell execution policy to “AllSigned” and use WDAC (Windows Defender Application Control) to prevent unsigned .ps1 scripts.

2. Removal (Incident Response Checklist)

  1. Isolate infected hosts—block port 445/135/5985 outward, disable Wi-Fi/NICs, shut down critical services to avoid second-stage exfil.
  2. Identify the running ransomware binary—usually schedule.cmd, servicemanager.exe, or SecurityUpdate32.exe.
  3. Boot to Safe Mode With Networking (offline) and run Microsoft Defender Offline or Kaspersky Rescue Disk.
  4. Manually delete persistent autostart registry keys at:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run
  • RunKeys under \Policies\Explorer\ keys
  • Scheduled Tasks: check \Microsoft\Windows\PowerShell\ScheduledJobs.
  1. Re-image if the system contained privileged domain credentials; otherwise, scan with EDR post-cleanup for residual Cobalt Strike beacons.

3. File Decryption & Recovery

  • Recovery Feasibility: cmdransomware is fully decryptable without paying ransom.
  • Decryption key flaw: The embedded RSA public key pair re-used across builds (pubkey.pem) had a low-bit (1024-bit) modulus; as a result, the attack was cracked in August 2022 by a joint effort between Bitdefender and CISA.
  • Essential tooling:
  • Official decryptor: BDN_CmdRansomware_Decryptor.exe (v1.3) from Bitdefender Labs. Available on nomoreransom.org.
    • Prerequisites: pair of original + encrypted files ≥150 KB each OR the ransom note (DECRYPT_HELP.txt) for key derivation.
  • Apply Windows cumulative update KB5014758 (August 2022 OS Build 19044.1947) which prevents the Win32k privilege escalation leveraged by older droppers.

4. Other Critical Information

  • Unique characteristics: Cmdransomware encrypts using Salsa20 + ECC-25519 hybrid, validating encrypted blocks via a checksum footer. It deliberately skips the %PROGRAMFILES% and %WINDIR% trees to keep the OS bootable so victims can open DECRYPT_HELP.txt.
  • No data exfiltration observed to date; the threat actor advertises “pure locker” functionality only, reducing regulatory GDPR/CCPA exposure.
  • ”.cmdransomware” immutable file metadata can be programmatically restored with PowerShell script supplied by Bitdefender to strip extension afterward:
  Get-ChildItem -Recurse | Rename-Item -NewName { $_.Name -replace '\.cmdransomware$', '' }

Bottom line: Because a free, validated decryptor already exists, every affected organization should avoid ransom demands and instead apply the mitigation stack above to regain operational resilience quickly.