Executive Summary

CVE-2026-51844 is a stack buffer overflow vulnerability found in Tenda AC7 routers running firmware version V15.03.06.44 and possibly earlier versions.

The vulnerability exists in the /goform/AdvSetMacMtuWan interface, specifically in the cloneType parameter.

The issue arises because the check_param_changed method uses the strcpy function to copy user-controlled input into a stack buffer without validating the size, which can lead to a stack overflow.

Attackers can exploit this by sending a specially crafted HTTP POST request with an excessively long cloneType value, triggering the overflow.

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Impact Analysis

This vulnerability can allow attackers to cause denial-of-service (DoS) conditions by crashing the router.

More critically, it may enable remote arbitrary code execution, allowing attackers to run malicious code on the affected device.

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Detection Guidance

This vulnerability can be detected by sending a crafted HTTP POST request to the /goform/AdvSetMacMtuWan interface with an excessively long cloneType parameter value.

A detection method involves monitoring for unusual or malformed HTTP POST requests targeting the /goform/AdvSetMacMtuWan endpoint, especially those containing abnormally long cloneType parameters.

For active testing, you could use tools like curl or custom scripts to send a POST request with a long cloneType parameter to see if the device behaves unexpectedly (e.g., crashes or restarts).

• Example curl command to test the vulnerability: curl -X POST http://<router-ip>/goform/AdvSetMacMtuWan -d "cloneType=$(python -c 'print("A"*1000)')"

Additionally, network intrusion detection systems (NIDS) can be configured to alert on HTTP POST requests to /goform/AdvSetMacMtuWan with unusually long cloneType parameters.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the vulnerable /goform/AdvSetMacMtuWan interface to trusted networks or IP addresses only.

Disabling remote management or administration features on the Tenda AC7 router can reduce exposure to this vulnerability.

Monitor the router for unusual behavior such as crashes or reboots that may indicate exploitation attempts.

Apply any available firmware updates or patches from the vendor that address this vulnerability once they become available.

As a temporary measure, consider implementing network-level protections such as firewall rules to block suspicious HTTP POST requests targeting /goform/AdvSetMacMtuWan.

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