How to remediate – Netdynamics ndcgi.exe Previous User Session Replay

1. Introduction

The Netdynamics ndcgi.exe Previous User Session Replay vulnerability allows attackers to potentially hijack user sessions on a remote web server. This means an attacker could gain access as legitimate users, compromising sensitive data and system functionality. Web servers running vulnerable versions of the ndcgi.exe file are affected. A successful exploit may lead to complete confidentiality, integrity, and availability loss for targeted sessions.

2. Technical Explanation

The vulnerability exists because some versions of the ndcgi.exe file do not properly manage user session data. This allows an attacker to potentially replay previous sessions, gaining unauthorised access. The CVE-2001-0922 identifier is associated with this issue. An example attack involves sending crafted requests to the vulnerable ndcgi.exe script, mimicking a legitimate user’s actions.

• Root cause: Insufficient session management within the ndcgi.exe file.
• Exploit mechanism: An attacker sends malicious requests designed to replay existing sessions. This could involve manipulating cookies or other session identifiers.
• Scope: Web servers running Netdynamics web server software with a vulnerable version of ndcgi.exe.

3. Detection and Assessment

Confirming the presence of the vulnerable file is the first step. A thorough assessment involves checking for specific versions known to be affected.

• Quick checks: Use the ls -l /cgi-bin/ndcgi.exe command to check if the file exists on your server.
• Scanning: Nessus vulnerability ID [ID number not provided in context] may detect this issue, but could be a false positive.
• Logs and evidence: Check web server logs for unusual activity related to ndcgi.exe or session handling.

ls -l /cgi-bin/ndcgi.exe

4. Solution / Remediation Steps

Removing the vulnerable file is the recommended solution.

4.1 Preparation

• Ensure you have a rollback plan in place, which involves restoring the backup if needed.
• A change window may be required depending on your organisation’s policies.

4.2 Implementation

1. Step 1: Remove the ndcgi.exe file from the /cgi-bin directory using the command rm /cgi-bin/ndcgi.exe.
2. Step 2: Restart the web server to apply the changes.

4.3 Config or Code Example

Before

-rw-r--r-- 1 root root [file size] [date] /cgi-bin/ndcgi.exe

After

ls -l /cgi-bin/  (ndcgi.exe should not be listed)

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue.

• Practice 1: Least privilege – limit the permissions granted to web server processes and files to reduce potential impact if exploited.

4.5 Automation (Optional)

#!/bin/bash
# Check if ndcgi.exe exists
if [ -f /cgi-bin/ndcgi.exe ]; then
  # Remove the file
  rm /cgi-bin/ndcgi.exe
  echo "Removed vulnerable ndcgi.exe file."
else
  echo "ndcgi.exe file not found."
fi

5. Verification / Validation

Confirm that the file has been removed and that the vulnerability is no longer present.

• Post-fix check: Run ls -l /cgi-bin/ndcgi.exe. The output should indicate that the file does not exist.
• Re-test: Re-run the Nessus scan to confirm the vulnerability is resolved.
• Smoke test: Verify basic web server functionality, such as accessing a standard webpage.
• Monitoring: Monitor web server logs for any errors related to missing files or session handling issues.

ls -l /cgi-bin/ndcgi.exe (should return "No such file or directory")

6. Preventive Measures and Monitoring

Update security baselines and implement regular patch reviews.

• Baselines: Update your web server security baseline to include a check for the presence of vulnerable ndcgi.exe files.
• Pipelines: Implement static analysis tools in your CI/CD pipeline to identify potentially insecure configurations or code.
• Asset and patch process: Establish a regular schedule for reviewing and applying security patches to all web server components.

7. Risks, Side Effects, and Roll Back

Removing the file may impact functionality if other applications rely on it.

• Roll back: Restore the backup of your web server configuration to revert the changes.

8. References and Resources

• Vendor advisory or bulletin: https://marc.info/?l=bugtraq&m=100681274915525&w=2
• NVD or CVE entry: CVE-2001-0922
• Product or platform documentation relevant to the fix: No specific documentation provided in context.