Gunra Ransomware: SafeBreach Coverage for CISA Alert AA26-222A

Summary

Gunra is a Conti-derived ransomware-as-a-service (RaaS) operation that follows a double-extortion model. The group targets multiple sectors by exploiting vulnerabilities in internet-facing firewalls and VPN appliances for initial access. After compromise, operators conduct credential dumping, lateral movement, and data exfiltration before deploying ransomware encryption payloads.

Investigation

A joint investigation by the FBI, CISA, NSA, and international partners documented Gunra’s use of Tor-based leak sites and its evolution into a structured RaaS operation. Investigators observed exploitation of FortiOS authentication bypass vulnerabilities and abuse of legitimate administrative tools for malicious activity. The campaign also uses advanced techniques including MFA bypass through authentication process modification and SSH tunneling.

Mitigation

Organizations should prioritize patching internet-facing vulnerabilities, particularly CVE-2024-55591 and CVE-2025-24472. Network segmentation, strong MFA enforcement, and adherence to the principle of least privilege are critical defensive measures. Maintaining offline and segmented backups is also essential because Gunra operators frequently delete volume shadow copies to hinder recovery.

Response

If Gunra activity is detected, responders should preserve encrypted files, file timestamps, and system logs, particularly on Linux systems, to support potential key reconstruction. Security teams should monitor for unauthorized super-user accounts such as forticloud-sync and anomalous WMI activity. Incident response should also determine the scope of data exfiltration through cloud services including OneDrive and SharePoint.

Simulation Execution

Prerequisite: The Telemetry & Baseline Pre-flight Check must have passed.

Rationale: This section details the precise execution of the adversary technique (TTP) designed to trigger the detection rule. The commands and narrative MUST directly reflect the TTPs identified and aim to generate the exact telemetry expected by the detection logic. Abstract or unrelated examples will lead to misdiagnosis.

• Attack Narrative & Commands: The adversary has gained an initial foothold and aims to exfiltrate VDI (Virtual Desktop Infrastructure) credentials. To bypass network inspection, the attacker first initiates an SSH tunnel to their C2 server using local port forwarding (-L). Simultaneously, they execute a custom sniffing tool named sniff.exe with a command-line argument targeting VDI traffic to capture credentials in transit. This dual-action approach is designed to mask the malicious traffic within an encrypted tunnel while the sniffer captures the cleartext/handshake data from the VDI session.

• Regression Test Script:

  # 1. Create a dummy 'sniff.exe' to simulate the sniffing tool
  $sniffPath = "$env:TEMPsniff.exe"
  "This is a dummy sniffer" | Out-File -FilePath $sniffPath -Encoding ascii
  
  # 2. Create a dummy 'ssh.exe' or use the system one to trigger the tunneling logic
  # We will use the real ssh.exe if available, or simulate the process call
  # To ensure the detection logic 'Image|endswith: ssh.exe' matches:
  
  Write-Host "[+] Starting Simulation: SSH Tunneling and VDI Sniffing" -ForegroundColor Cyan
  
  # Step A: Execute the simulated sniffing tool (Targeting VDI)
  Start-Process -FilePath $sniffPath -ArgumentList "capture --target VDI" -WindowStyle Hidden
  
  # Step B: Execute SSH Tunneling (Targeting -L flag)
  # Note: We use a dummy command to prevent actual connection attempts if ssh.exe is present
  # but ensures the CommandLine contains the required flags.
  Start-Process -FilePath "ssh.exe" -ArgumentList "-L 8080:localhost:80 user@127.0.0.1" -WindowStyle Hidden
  
  Write-Host "[+] Simulation commands executed. Check telemetry for detection." -ForegroundColor Green

• Cleanup Commands:

  # Remove the simulated malicious files
  Remove-Item -Path "$env:TEMPsniff.exe" -Force -ErrorAction SilentlyContinue
  Write-Host "[+] Cleanup complete." -ForegroundColor Yellow