coba

[Content by Gemini 2.5]

Cobra Ransomware ({{ $json.extension }} = “.coba”) – Community Resource

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware appends the exact extension “.coba” to every encrypted file.
  • Renaming Convention:
    Original: Project_Report_Q2.docx → After encryption: Project_Report_Q2.docx.coba
    Folders also receive a ransom note named readme.txt at their root.

2. Detection & Outbreak Timeline

  • Approximate Start Date / Period: First samples reported in late March 2024 through an affiliate campaign of STOP/DJVU family. Widespread detections peaked between April 15 – May 5 2024.

3. Primary Attack Vectors

| Method | Explanation | Practical Example |
|——–|————-|——————-|
| Malvertising & Cracked-Software Bundles | Infections often enter via “warez” torrents or software-keygen sites. |受害者 drops a “Driver Booster Pro 12 + Crack.exe” → drops .coba |
| Phishing Emails w/ Malicious Attachments | Zip or ISO files containing the loader. | Subject: “New PO April 28 (URGENT).pdf.iso” → runs .exe that downloads Coba |
| Exploitation of CVE-2023-34362 (MOVEit Transfer) | Secondary lateral propagation after MOVEit compromise. | Initial foothold on DMZ web server, then executes .coba on file-shares. |
| RDP / SMBv1 Brute Force | Older Windows hosts with poorly-enforced RDP passwords. | Successful login on 3389 → copy of trojan.exe dropped to CIFS share, executed via psExec. |

Remediation & Recovery Strategies:

1. Prevention

  1. Block Threat Matrix at Edge
    • Egress firewall rules denying executables from %TEMP%, %APPDATA%, \Users\<user>\Downloads.
    • EDR rules to terminate unsigned .exe files spawned by browsers or Office executables.
    • DNS sink-hole known C2 domains (SnatchLoader/DJVU list).

  2. User-Focused Controls
    • Disable Macros by default (HKCU\Software\Microsoft\Office\16.0\Word\Security\VBAWarnings=2).
    • Train staff on “cracked-software = ransomware.”
    • Require MFA for all RDP (including jump boxes).

  3. System Hardening
    • Patch MOVEit/Citrix gateways monthly.
    • Disable SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
    • Segment file shares with write restrictions – avoid domain admins having global write access.

2. Removal

  1. Isolate
    • Disconnect from network; disable Wi-Fi and pull cables.
    • Bookmarking Shadow-copy and Volume Shadow Service (VSS) stops automatic removal of shadow copies (task: avenger.exe 24hr loop).

  2. Identify Persistence
    • Open Task Manager → Details → look for updatewin.exe, edge.js, msedge.exe outside Program Files.
    • Autoruns → hide MS/Windows signed → check Run keys, Scheduled Tasks.

  3. Delete Malicious Artifacts
    • Safe-Mode w/ Command Prompt.
    • del /f "%APPDATA%\updatewin.exe"
    • schtasks /delete /tn "SystemUpdates" /f

  4. Scan & Confirm
    • Full offline scan with Windows Defender (engine 1.401.100.0 or later).
    • Optional: Malwarebytes 4.6.13 with “scan within archives” enabled.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Coba == STOP/DJVU variant v0698 (5-digit earlier versions used .mmpa, .nooa, etc.).
    If your file pairs show t1 in personal ID at end of ransom note → offline key → decryptable via Emsisoft Decrypter 1.0.0.23 (May 2024).
    If ID is online (random) → no free decryptor, rely on backups or shadow copies.

  • Essential Tools / Patches

  1. Emsisoft STOP-DJVU Decrypter (SHA256: 3e7d38b28…) – portable, saves logs.
  2. ShadowExplorer 0.9 to rip untouched shadow copies.
  3. Windows 10/11 cumulative patch KB5033372 – addresses 3 exploited CVEs connected to DJVU.

4. Other Critical Information

  • Unique Traits
    – Attempts to terminate Windows Backup, Veeam, Acronis processes before encryption.
    – Writes SOFTWARE\tiqr registry key to log file-count and payment status—a handy IOC.
  • Broader Impact
    – Early alerts show compromise of 150+ small accounting firms in the U.S., primarily via TurboTax cracked versions.
    – Business email compromise (BEC) spiral in 20 % of cases: crooks resell corporate credentials from C2 logs.

Quick Triage Checklist

□ Disinfected & rebooted
□ Shadow copies still present? (vssadmin list shadows) → copy important docs offline
□ Ran STOP-DJVU decrypter with sample .coba + original file from backup → verify decryption success/failure
□ Enabled “Controlled Folder Access” (ASR rule) via Intune post-cleanup

Stay vigilant, update engines daily, and never pay—there’s a rising success rate with free decryptor updates.