How to remediate – Zincite.A (MyDoom.M) Backdoor Detection

1. Introduction

Zincite.A (MyDoom.M) is a backdoor that allows an attacker remote access to compromised systems. It’s typically installed by the MyDoom.M virus, and affects Windows-based machines. Successful exploitation could lead to data theft, system control, or use of the infected host for malicious purposes. Impact on confidentiality, integrity, and availability is likely if exploited.

2. Technical Explanation

• Root cause: The worm installs a backdoor service without proper authentication or authorization.
• Exploit mechanism: After initial infection by MyDoom.M, the backdoor listens for incoming connections on a specified port (typically TCP 3137). An attacker can connect to this port and execute commands as SYSTEM. A simple example payload is `netcat 3137`.
• Scope: Windows operating systems are affected. Specific versions depend on the MyDoom.M variant.

3. Detection and Assessment

Confirming a Zincite.A infection involves checking for the backdoor service and associated files. A quick check is to look for listening ports, while thorough assessment requires scanning with an anti-malware tool.

• Quick checks: Use `netstat -ano | findstr 3137` to see if a process is listening on port 3137.
• Scanning: Nessus signature ID 4b1ba661 and 73403fd6 can detect Zincite.A. These are examples only, as scanner coverage varies.
• Logs and evidence: Check the Windows Event Logs for suspicious service creation events or unusual network connections. Look for entries related to new services starting without a clear owner.

netstat -ano | findstr 3137

4. Solution / Remediation Steps

Fixing this issue requires verifying compromise and potentially reinstalling the system. Follow these steps carefully to ensure complete removal of the threat.

4.1 Preparation

• Ensure you have access to clean installation media and anti-malware tools. A roll back plan is to restore from backup or revert the snapshot.
• A change window may be needed, especially for production systems. Approval from IT security lead is recommended.

4.2 Implementation

1. Step 1: Run a full system scan with an up-to-date anti-malware solution. Remove any detected threats.
2. Step 2: Check the Services list (services.msc) for suspicious entries, especially those without clear descriptions or owners.
3. Step 3: If you find unknown services, attempt to stop them and delete their associated files from the file system. Be careful not to remove essential system services.
4. Step 4: If compromise is confirmed, consider reinstalling the operating system from clean media. This is the most reliable method of removal.

4.3 Config or Code Example

Before

(Example - suspicious service entry in services.msc)
Name: UnknownService
Description: No description available
Status: Running

After

(Example - after removing the service)
No "UnknownService" entry present in services.msc. Associated files removed from file system.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of infection. Least privilege reduces impact, while a robust patch cadence limits exposure.

• Practice 1: Implement least privilege access control. Limit user accounts to the minimum necessary permissions to reduce the potential damage from an exploited backdoor.
• Practice 2: Maintain a regular patch cadence for your operating systems and applications. Promptly apply security updates to address known vulnerabilities that worms like MyDoom.M exploit.

4.5 Automation (Optional)

# PowerShell example - scan for suspicious services (use with caution!)
Get-Service | Where-Object {$_.Description -eq "" -and $_.Status -eq "Running"} | Select-Object Name, Status

5. Verification / Validation

Confirm the fix by re-scanning and checking for the backdoor service. A smoke test should verify core system functionality remains intact.

• Post-fix check: Run `netstat -ano | findstr 3137`. Expected output should show no process listening on port 3137.
• Re-test: Re-run the Nessus scan using signature IDs 4b1ba661 and 73403fd6 to confirm the vulnerability is no longer detected.
• Smoke test: Verify basic system functionality, such as network connectivity, user login, and application access.
• Monitoring: Monitor Windows Event Logs for suspicious service creation events or unusual network connections. Example query: Filter event ID 7036 (service start) for unknown services.

netstat -ano | findstr 3137

6. Preventive Measures and Monitoring

Update security baselines, implement input validation where possible, and maintain a strong patch process to prevent future infections. For example, use CIS controls or GPOs/Intune settings.

• Baselines: Update your Windows security baseline to include restrictions on service creation and execution of unknown files.
• Pipelines: Integrate static code analysis (SAST) into your development pipeline to identify potential vulnerabilities in custom applications.
• Asset and patch process: Implement a regular patch review cycle, aiming for patches to be applied within 72 hours of release.

7. Risks, Side Effects, and Roll Back

Removing the backdoor service may disrupt dependent applications. Reinstalling the OS will result in data loss if not backed up. Roll back involves restoring from backup or snapshot.

• Roll back: 1) Restore from backup. 2) If a snapshot was taken, revert to it.

8. References and Resources

• Vendor advisory or bulletin: http://www.nessus.org/u?4b1ba661
• NVD or CVE entry: No specific CVE for Zincite.A itself, but see MyDoom.M related entries on the NVD website.