Executive Summary

The CVE-2026-36794 vulnerability affects the Tenda W3 Wireless Router version 1.0.0.3(2204). It is a stack-based buffer overflow in the R7WebsSecurityHandler function, which handles HTTP requests involving username and password parameters.

The vulnerability occurs because the router copies the username and password parameters into a fixed-size stack buffer without checking their length or sanitizing the input. Specifically, the username parameter can be excessively long and is copied using strcpy, which does not limit the size, leading to an overflow of the stack buffer.

This overflow allows an attacker to overwrite adjacent memory on the stack, which can cause the router to crash or reboot (denial of service) or potentially allow arbitrary code execution.

The attack is carried out by sending a specially crafted HTTP request to the R7WebsSecurityHandler CGI endpoint with a non-empty password and an overly long username.

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Impact Analysis

This vulnerability can impact you by causing a denial of service (DoS) on your Tenda W3 Wireless Router. An attacker can send a crafted HTTP request that triggers a stack overflow, causing the router to crash or reboot unexpectedly.

In some cases, the vulnerability might allow an attacker to execute arbitrary code on the device, which could lead to further compromise of the router and the network it protects.

Such disruptions can lead to loss of network connectivity, potential exposure of sensitive data, and unauthorized control over your network device.

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Detection Guidance

This vulnerability can be detected by monitoring for crafted HTTP requests sent to the R7WebsSecurityHandler CGI endpoint on the Tenda W3 Wireless Router V1.0 with firmware version V1.0.0.3(2204). Specifically, detection involves identifying HTTP requests that include an overly long username parameter combined with a non-empty password parameter.

A practical approach is to capture and analyze HTTP traffic targeting the router's R7WebsSecurityHandler endpoint, looking for unusually long username values that could trigger the stack overflow.

• Use network packet capture tools like tcpdump or Wireshark to filter HTTP requests to the router's IP on the relevant port (usually port 80 or 443).
• Example tcpdump command to capture HTTP requests to the router: tcpdump -i <interface> host <router_ip> and tcp port 80 -w capture.pcap
• Analyze captured traffic for HTTP POST or GET requests to the R7WebsSecurityHandler endpoint containing username parameters with suspiciously long values.
• Alternatively, use curl or similar tools to test the endpoint by sending crafted requests with long username parameters to verify if the device is vulnerable.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable R7WebsSecurityHandler CGI endpoint to trusted networks only, such as by firewall rules or network segmentation.

Avoid exposing the router's management interface to untrusted networks or the internet to reduce the attack surface.

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

In the meantime, monitor the router for crashes or reboots that could indicate exploitation attempts.

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