Impact Analysis

This vulnerability can have severe impacts including service disruption and unauthorized control.

• Service crash due to stack corruption, leading to denial of service.
• Potential remote code execution (RCE) by an authenticated attacker, which could allow them to execute arbitrary code on the device.
• Compromise of the router's security, potentially allowing attackers to intercept or manipulate network traffic.

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Executive Summary

CVE-2026-11522 is a stack-based buffer overflow vulnerability found in the Tenda W20E router, specifically in the formSetPortMirror function located in the /goform/setPortMirror file.

The vulnerability arises when an authenticated attacker manipulates the portMirrorMirroredPorts parameter with input exceeding 256 bytes. The function uses sprintf to copy this input into a fixed-size 256-byte stack buffer without proper bounds checking.

This improper handling can overwrite critical stack data such as the saved Link Register (LR), potentially causing the service to crash or allowing remote code execution (RCE).

Exploitation requires authentication and has been demonstrated with a proof-of-concept payload of 1000 'A' characters sent to the vulnerable endpoint.

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Detection Guidance

This vulnerability can be detected by attempting to send a specially crafted HTTP POST request to the /goform/setPortMirror endpoint on the Tenda W20E router running version 15.11.0.6. The request should include the portMirrorMirroredPorts parameter with a payload exceeding 256 bytes, such as 1000 'A' characters, to test for a stack-based buffer overflow.

Detection requires authentication on the device, as exploitation needs authenticated access.

A sample command using curl to test the vulnerability could be:

• curl -X POST -d "portMirrorMirroredPorts=$(python3 -c 'print("A"*1000)')" http://<router-ip>/goform/setPortMirror --user <username>:<password>

Monitoring for crashes or abnormal behavior on the device after sending such a request can indicate the presence of the vulnerability.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the router's management interface to trusted users only, ensuring that only authenticated users can reach the /goform/setPortMirror endpoint.

Limit network exposure by placing the device behind a firewall or VPN and disabling remote management if not needed.

Monitor the device for unusual crashes or behavior that could indicate exploitation attempts.

Apply any available firmware updates or patches from the vendor once released to fix the vulnerability.

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