How to remediate – UPnP Internet Gateway Device (IGD) External IP Address Reachable

1. Introduction

The UPnP Internet Gateway Device (IGD) External IP Address Reachable vulnerability allows an external party to read the public IP address assigned to your router. This information can be used for reconnaissance, potentially leading to targeted attacks against other services on your network. Routers supporting the Internet Gateway Device protocol are typically affected. A successful exploit has a low impact on confidentiality but minimal impact on integrity or availability.

2. Technical Explanation

The vulnerability occurs because Universal Plug and Play (UPnP) IGD allows remote retrieval of the router’s external IP address via its data service. This is enabled by default on many routers, exposing this information unnecessarily. An attacker can query the device to obtain this IP address without authentication.

• Root cause: The UPnP IGD protocol exposes the external IP address in a publicly accessible data service.
• Exploit mechanism: An attacker sends an HTTP request to the router’s UPnP interface, requesting the external IP address. This can be done using tools like `curl` or dedicated network scanners. For example: http://<router_ip>:4810/setupXML
• Scope: Routers from various manufacturers supporting the UPnP IGD standard are affected, including those running older firmware versions.

3. Detection and Assessment

You can confirm if your system is vulnerable by checking for an open UPnP port and retrieving the external IP address. A thorough method involves using a network scanner.

• Quick checks: Use `netstat -tulnp | grep 4810` to check if port 4810 (the default UPnP port) is listening.
• Scanning: Nessus vulnerability ID 16293 can detect this issue. Other scanners may have similar signatures.
• Logs and evidence: Router logs might show requests to the UPnP interface, though specific logging varies by vendor.

netstat -tulnp | grep 4810

4. Solution / Remediation Steps

The best way to fix this issue is to disable IGD or restrict access to trusted networks.

4.1 Preparation

• Ensure you have console or web interface access to the router in case of issues. A roll back plan involves restoring the previous configuration file.
• This change may require a brief service interruption while the router restarts. Approval from your network team might be needed.

4.2 Implementation

1. Step 1: Log into your router’s web interface.
2. Step 2: Navigate to the UPnP settings (usually found under Advanced Settings, Security, or Firewall).
3. Step 3: Disable UPnP entirely if you do not require it.
4. Step 4: If UPnP is needed, restrict access to only trusted internal networks by configuring firewall rules.
5. Step 5: Save the changes and restart your router.

4.3 Config or Code Example

Before

UPnP: Enabled, Access Control: Any

After

UPnP: Disabled, Access Control: Local Network Only (if enabling is required)

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 1: Least privilege – disable unnecessary services like UPnP to reduce the attack surface.
• Practice 2: Network segmentation – restrict access to sensitive internal resources using firewall rules.

4.5 Automation (Optional)

# Example Ansible task to disable UPnP on routers supporting a specific API
- name: Disable UPnP
  uri:
    url: "http://<router_ip>/api/upnp"
    method: POST
    body: '{"enabled": false}'
    status_code: 200
  # Note: This is a simplified example and requires router API credentials.

5. Verification / Validation

Confirm the fix by checking that port 4810 is no longer accessible or that you can’t retrieve the external IP address via UPnP.

• Post-fix check: Run `netstat -tulnp | grep 4810`. The output should not show any processes listening on port 4810.
• Re-test: Re-run the earlier detection method (e.g., using `curl http://<router_ip>:4810/setupXML`). You should receive an error or no response.
• Monitoring: Monitor router logs for any failed attempts to access the UPnP interface, indicating potential reconnaissance activity.

netstat -tulnp | grep 4810

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type. Use “for example” to keep advice conditional, not prescriptive.

• Baselines: Update your router security baseline to include disabling UPnP or restricting access.
• Pipelines: Implement configuration management tools to enforce consistent settings across all routers.
• Asset and patch process: Regularly review router firmware for updates and apply them promptly.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Disabling UPnP may break applications that rely on it (e.g., some online games).
• Risk or side effect 2: Restricting access incorrectly could block legitimate network traffic.
• Roll back: Step 1: Log into your router’s web interface. Step 2: Re-enable UPnP and restore the original access control settings. Step 3: Save the changes and restart your router.

8. References and Resources

• Vendor advisory or bulletin: Check your router manufacturer’s website for specific security advisories related to UPnP.
• NVD or CVE entry: https://nvd.nist.gov/vuln/detail/CVE-2018-1336
• Product or platform documentation relevant to the fix: Refer to your router’s manual for instructions on disabling UPnP.