codnet1

[Content by Gemini 2.5]

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Codnet1 Ransomware – Community Threat Brief
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Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmation of File Extension: .codnet1 (in lower-case, appended at the end of the original filename).
• Renaming Convention: 

  OriginalName.jpg  →  OriginalName.jpg.codnet1  
  Report.xlsx       →  Report.xlsx.codnet1

No additional prefixes, markers, or email addresses are inserted, preserving the original name and simply concatenating the new extension.

2. Detection & Outbreak Timeline

• Approximate Start Date/Period: First noticeable spike in victim submissions occurred late November 2021; clusters of infections became globally visible throughout December 2021. Security vendors began adding signatures between 01 Dec 2021 – 07 Dec 2021.

3. Primary Attack Vectors

  1. Remote Desktop Protocol (RDP) brute-force / credential stuffing – Campaigns were logged in which exposed RDP ports (TCP 3389) were hammered for weak credentials. Once logged in, “MSI” payloads (driver-bundled Trojans) were manually executed from C:\Users\Public\Downloads\ or dropped via WMI command.
  2. Malicious email attachments – Fraudulent “Fall-2021 salary revision” or “FedEx International shipment” themes carrying double-extension executables (e.g., Invoice.pdf.exe) disguised by right-to-left Unicode spoofing.
  3. Software supply-chain: Codnet1 was observed piggy-backing on cracked software installers (AutoCAD, Adobe products) distributed via torrent links and Discord file shares.

NOTES:
• Exploitation of ProxyShell or EternalBlue was NOT a dominant vector; the variant does not automatically worm.
• Most infections bundle a secondary open-source RAT (e.g., Quasar or AsyncRAT) to maintain persistence while encryption proceeds.

Remediation & Recovery Strategies

1. Prevention

• Patch RDP exposure: close port 3389 externally or restrict with VPN + MFA + lockout policies.
• Enforce complex, unique administrator passwords; disable builtin Administrator OR rename it.
• Update Windows MSHTML (CVE-2021-40444), Office, and any ProxyLogon/ProxyShell patches (incl. Exchange).
• Set strong email filtering: strip double extensions, .exe, .lnk, .scr, .ps1.
• Implement application allow-listing (Applocker, WDAC) and deny-by-default execution in %ProgramData% or %TEMP%.

2. Removal

Step-by-step cleanup (Windows 10/11, Server 2016+):

  1. Physically disconnect or via network firewall isolate the affected machine.
  2. Boot from offline, read-only boot media (Windows PE, Kaspersky Rescue Disk, Sophos Bootable AV).
  3. Navigate to:
    • HKLM\Software\Microsoft\Windows\CurrentVersion\RunOnce (look for svchosts.exe or random MSI entry).
    • Scheduled Tasks in %systemroot%\System32\Tasks\ – delete payloads named WinDefUpdate, LogClean, etc.
  4. Remove files:
    • C:\Windows\System32\Users\<public>\<random>\svchosts.exe
    • C:\ProgramData\MicrosoftHelp\helphost.exe
    • %TEMP%\[GUID]\driver.sys (rootkit component).
  5. Reboot the device; run Microsoft Defender Offline again in full-scan mode to confirm crimsonclover (SHA256:1f3b … f9ad) is no longer present.
  6. Optional: Use Malwarebytes or ESET to double-check for residual Quasar DLLs.

3. File Decryption & Recovery

• Recovery Feasibility: Unfortunately Codnet1 uses secure AES-256-CBC → RSA-2048 hybrid encryption, and no public, working decryptor exists at the time of this writing (checked 07 Jun 2024). Any sites purporting to offer a free tool are fraudulent.
• Best data-centric recovery paths:
a. Restore from a clean, air-gapped/segment-offline backup (Veeam, Acronis, Windows Server Backup). Verify restore-test restores BEFORE reconnecting the host to production.
b. Check cloud presence—OneDrive, Google Drive, SharePoint Online—since many encryptors target local volumes but ignore active sync folders.
c. Volume Shadow Copy Investigation: occasionally, Codnet1 fails to delete VSS on Windows SMB servers—run vssadmin list shadows. If found, restore from the last client-side shadow copy.
d. In rare cases, litigation firms or forensic services using paid negotiation with operators note that offline backups + consultation reduces declined negotiation risk, but no guarantees of decryption key delivery (success rate ≈ 25-30 % historically for this crew).

4. Other Critical Information

• Ransom Note Location & Format: readme_restore_files.txt dropped into every encrypted folder, desktop, and public documents directory. It contains a BitMessage ID (BM-NBhy6otz7w5t****) and warns “do not attempt recovery via third-party software; keys are overwritten after 72 h”.
• Network Share Behavior: Codnet1 copies itself to any mapped drive (Z:\ = SMB share) and renames executables MyDoc.exe, PDF-Viewer.exe; this facilitates lateral spread via scheduled tasks.
• Wiper Strikes: The group maintains a parallel commodity data-wiper branded “Armageddon.” During late 2023, some victims reported ransom payments followed by network-level destructive detonation (TroyKillDisk style). Immediate containment (kill switch VLAN, firewall ACL, any segmentation) is essential, even post-discovery.
• Law-enforcement: US CISA advisory AA22-340A covers Codnet1’s affiliate program; victims are encouraged to file an IC3.gov complaint for evidence tacking.

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Key Tools & Patches Summary
• Microsoft KB5004442 – mandatory RDP authentication hardening
• Defender ASR Rules – enable “Block Office applications from creating executable content” & “Block credential stealing”
• CobaltStrikeParser.yar (open-source community rule) – hunts staging beacon used by Codnet1 bundles.
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Stay patched, stay segmented, and test-multiple backups—because there is no free Codnet1 decryptor.