How to remediate – Web Server UPnP Detection

Contents

1. Introduction

The Web Server UPnP Detection vulnerability means a web server is advertising its Universal Plug and Play (UPnP) capabilities. This allows devices on the network to discover and potentially interact with services running on the server, which could expose them unnecessarily. Systems commonly affected are those hosting websites or applications using web servers like Apache, IIS, or Nginx. A successful exploit could lead to information disclosure or remote code execution. Confidentiality, integrity, and availability may be impacted.

2. Technical Explanation

The vulnerability occurs because the web server responds to UPnP discovery requests, revealing details about its services. Attackers can use this information to target SOAP requests to these services. This is not a direct flaw in the web server itself but rather an exposure of underlying device functionality. There isn’t a specific CVE associated with simply *detecting* UPnP; exploitation relies on vulnerabilities within the discovered UPnP services themselves.

Root cause: The web server allows responses to UPnP discovery requests, broadcasting service information.
Exploit mechanism: An attacker queries the web server for UPnP details then attempts to interact with exposed SOAP endpoints using crafted requests. For example, an attacker could attempt to access a vulnerable media server advertised via UPnP.
Scope: Web servers running on various platforms (Windows, Linux) are affected if UPnP is enabled on the underlying system or services they host.

3. Detection and Assessment

You can confirm this vulnerability by checking for a response to a UPnP discovery request. A thorough method involves using a network scanner to identify all UPnP devices.

Quick checks: Use `curl -v http://[target_ip]:[port]` and look for responses containing “UPnP” or similar keywords in the headers.
Scanning: Nessus plugin ID 10423 can detect this issue. Other scanners may have similar capabilities, but results should be verified.
Logs and evidence: Web server access logs might show requests to specific UPnP ports (e.g., 49152). Event logs on Windows systems could indicate UPnP activity.

curl -v http://192.168.1.100:80

4. Solution / Remediation Steps

The best way to fix this is to filter incoming traffic to the port used for UPnP if it’s not needed. If you don’t need UPnP, disable it entirely.

4.1 Preparation

Ensure you have access to firewall settings or network configuration tools. A roll back plan is to restore the previous snapshot.
Changes may require a maintenance window and approval from your security team.

4.2 Implementation

Step 1: Identify the port used for UPnP (typically 49152).
Step 2: Configure your firewall to block incoming traffic on that port. For example, using `iptables -A INPUT -p tcp –dport 49152 -j DROP` on Linux.
Step 3: Restart the web server service.

4.3 Config or Code Example

Before

# No firewall rule blocking port 49152

After

iptables -A INPUT -p tcp --dport 49152 -j DROP

4.4 Security Practices Relevant to This Vulnerability

Least privilege is important here, as limiting network access reduces the impact of exposed services. Input validation can prevent malicious requests from being processed if UPnP is required.

Practice 1: Least privilege – only allow necessary ports and services to be accessible.
Practice 2: Network segmentation – isolate sensitive servers from untrusted networks.

4.5 Automation (Optional)

If using infrastructure-as-code, you can automate firewall rule creation.

# Example Ansible snippet
- name: Block UPnP port
  iptables:
    chain: INPUT
    protocol: tcp
    destination_port: 49152
    jump: DROP

5. Verification / Validation

Confirm the fix by checking that you can no longer access the UPnP information from outside the server.

Post-fix check: Run `curl -v http://[target_ip]:[port]` again; it should either time out or return an error.
Re-test: Re-run the Nessus scan (plugin ID 10423) to confirm the vulnerability is no longer detected.
Smoke test: Verify that your website or application continues to function as expected.
Monitoring: Check web server logs for failed connection attempts on port 49152.

curl -v http://192.168.1.100:80

6. Preventive Measures and Monitoring

Regular security baselines should include checks for unnecessary services like UPnP. Automated scanning in CI/CD pipelines can prevent similar exposures.

Baselines: Update your security baseline to disallow UPnP unless specifically required by a service.
Asset and patch process: Review server configurations regularly for unnecessary features or open ports.

7. Risks, Side Effects, and Roll Back

Risk or side effect 1: Blocking port 49152 may disrupt applications that use UPnP.
Roll back: Remove the firewall rule using `iptables -D INPUT -p tcp –dport 49152 -j DROP` and restart the web server service. Restore the snapshot if necessary.

8. References and Resources

Vendor advisory or bulletin: Not applicable for general UPnP detection.
NVD or CVE entry: Not applicable for general UPnP detection.
Product or platform documentation relevant to the fix: https://en.wikipedia.org/wiki/Universal_Plug_and_Play

Updated on October 26, 2025

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