Executive Summary

The CVE-2026-36809 vulnerability affects the Tenda W15E router, specifically in the formModifyWebAuthWhiteUser function. It is a buffer overflow issue caused by improper handling of the user-controlled HTTP parameter webAuthWhiteID.

An attacker can send a specially crafted HTTP request with a long webAuthWhiteID parameter along with certain other parameters set (webAuthWhiteUserType set to "mac", and webAuthWhiteUser and webAuthUserPwd not null) to trigger this buffer overflow.

This overflow occurs when the vulnerable code uses the webAuthWhiteID parameter in functions like printf and sprintf without proper bounds checking, leading to memory corruption.

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Impact Analysis

This vulnerability can cause a Denial of Service (DoS) on the affected Tenda W15E router.

The buffer overflow can crash the process handling the web authentication white list or cause device instability, potentially disrupting network connectivity and router functionality.

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Detection Guidance

This vulnerability can be detected by monitoring for crafted HTTP requests sent to the formModifyWebAuthWhiteUser CGI endpoint on the Tenda W15E router. Specifically, look for HTTP requests containing a long webAuthWhiteID parameter (e.g., "888*a" or longer) along with non-null parameters webAuthWhiteUserType, webAuthWhiteUser, and webAuthUserPwd, where webAuthWhiteUserType is set to "mac".

To detect such attempts, you can use network monitoring tools or intrusion detection systems to filter HTTP POST requests to the endpoint "/formModifyWebAuthWhiteUser" with suspiciously long webAuthWhiteID values.

Example command using tcpdump to capture HTTP POST requests to the vulnerable endpoint:

• tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep 'POST /formModifyWebAuthWhiteUser'

Alternatively, use tools like Wireshark to filter HTTP traffic for POST requests to "/formModifyWebAuthWhiteUser" and inspect the parameters for unusually long webAuthWhiteID values.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the web management interface of the Tenda W15E router to trusted networks or IP addresses to prevent unauthorized HTTP requests to the vulnerable endpoint.

Additionally, monitor the device logs and network traffic for signs of exploitation attempts involving the formModifyWebAuthWhiteUser function.

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

As a temporary workaround, consider disabling remote management features or blocking HTTP POST requests to the "/formModifyWebAuthWhiteUser" endpoint via firewall rules.

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