Executive Summary

The CVE-2026-36807 vulnerability affects the Tenda W15E router, specifically in the formAddWebAuthUser function of its firmware version V15.11.0.10.

This function processes HTTP parameters, including webAuthUserInfo, using functions like strchr and strncpy.

An attacker can exploit this vulnerability by sending a crafted HTTP request with an excessively long webAuthUserInfo parameter, which causes a buffer overflow.

This buffer overflow can lead to denial of service (DoS) conditions such as process crashes or device instability.

The vulnerable path is easily accessible, making exploitation straightforward.

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Impact Analysis

This vulnerability can be exploited to cause a denial of service (DoS) on the affected Tenda W15E router.

Exploitation may result in process crashes or device instability, potentially disrupting network connectivity and availability.

Since the vulnerable function is easily accessible via HTTP requests, attackers can trigger this impact remotely.

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Detection Guidance

This vulnerability can be detected by monitoring for HTTP requests targeting the formAddWebAuthUser function on the Tenda W15E router firmware version V15.11.0.10, specifically those containing an excessively long webAuthUserInfo parameter.

A crafted HTTP request with around 888 'a' characters followed by 50 or more newline characters in the webAuthUserInfo parameter can trigger the buffer overflow.

To detect potential exploitation attempts, you can capture and analyze HTTP traffic to the router's web interface and look for unusually long webAuthUserInfo parameters.

• Use a network packet capture tool like tcpdump or Wireshark to capture HTTP traffic on the router's management interface.
• Example tcpdump command to capture HTTP traffic on interface eth0: tcpdump -i eth0 -A 'tcp port 80'
• Filter captured HTTP requests for the formAddWebAuthUser endpoint and inspect the webAuthUserInfo parameter length.
• Alternatively, use curl or similar tools to send test requests with long webAuthUserInfo parameters to check if the device responds abnormally or crashes.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the router's web management interface to trusted networks or IP addresses to prevent unauthorized HTTP requests.

Monitor the device for signs of instability or crashes that may indicate exploitation attempts.

If possible, apply firmware updates or patches provided by the vendor that address this vulnerability.

In the absence of a patch, consider disabling remote web management or using alternative secure management methods.

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