Executive Summary

CVE-2026-36771 is a stack-based buffer overflow vulnerability found in the Tenda W3 Wireless Router firmware version 1.0.0.3(2204). It occurs in the formwrlSSIDset CGI handler when the wl_radio parameter is set to "0" and an attacker provides an excessively long index parameter. The vulnerability arises because the code uses sprintf to construct a configuration key prefix without properly validating the length of the index parameter, leading to a buffer overflow.

This flaw can be exploited by sending a specially crafted HTTP request to the formwrlSSIDset CGI endpoint with malicious parameters, causing the router to crash or reboot.

In some cases, this buffer overflow could potentially allow an attacker to execute arbitrary code on the device.

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Impact Analysis

This vulnerability can impact you by causing a Denial of Service (DoS) on the affected Tenda W3 Wireless Router. An attacker can exploit the buffer overflow to crash or reboot the device, disrupting network connectivity.

Additionally, there is a potential risk that an attacker could execute arbitrary code on the router, which might lead to further compromise of the device and the network it supports.

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious HTTP requests targeting the formwrlSSIDset CGI endpoint on the Tenda W3 Wireless Router. Specifically, detection involves identifying requests where the wl_radio parameter is set to "0" and the index parameter contains an excessively long value, which triggers the stack-based buffer overflow.

A practical detection method is to capture and analyze HTTP traffic to the router, looking for requests similar to the following pattern:

• HTTP GET or POST requests to /formwrlSSIDset with parameters wl_radio=0 and a very long index parameter.

Example command using curl to test for the vulnerability (for detection purposes only):

• curl -v "http://[router_ip]/formwrlSSIDset?wl_radio=0&index=$(python3 -c 'print("A"*500)')"

Network intrusion detection systems (NIDS) can be configured to alert on HTTP requests matching this pattern to detect potential exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the formwrlSSIDset CGI endpoint to trusted users only, such as by limiting management access to the router via firewall rules or network segmentation.

Additionally, monitoring and blocking suspicious HTTP requests with the wl_radio=0 parameter and unusually long index values can help prevent exploitation.

If possible, update the router firmware to a version that patches this vulnerability once it becomes available from the vendor.

As a temporary measure, consider disabling remote management features or the vulnerable CGI handler if the router's configuration allows.

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