Executive Summary

CVE-2026-6200 is a stack-based buffer overflow vulnerability found in the Tenda F456 router, version 1.0.0.5. It occurs in the HTTP daemon's function formWebTypeLibrary, which processes a user-supplied parameter called webSiteId.

The vulnerability arises because the webSiteId value is concatenated to a buffer using the strcat function without checking the length, allowing an attacker to overflow the buffer.

An attacker can exploit this by sending a specially crafted HTTP POST request to the /goform/webtypelibrary endpoint with an excessively long webSiteId parameter, causing the buffer overflow.

This overflow can lead to denial of service (DoS) or remote code execution (RCE) on the affected device.

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Impact Analysis

This vulnerability can have serious impacts including denial of service (DoS), where the device may crash or become unresponsive.

More critically, it can allow remote code execution (RCE), enabling an attacker to run arbitrary code on the affected router remotely.

Such exploitation could lead to full compromise of the device, potentially allowing attackers to intercept network traffic, alter device configurations, or use the device as a foothold for further attacks.

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious HTTP POST requests sent to the endpoint /goform/webtypelibrary with an unusually long webSiteId parameter.

A practical detection method is to capture and analyze network traffic for POST requests targeting /goform/webtypelibrary that contain excessively long or malformed webSiteId values.

• Use a network packet capture tool like tcpdump or Wireshark to filter HTTP POST requests to /goform/webtypelibrary.
• Example tcpdump command to capture relevant traffic: tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/webtypelibrary'
• Use curl or similar tools to test the endpoint by sending a crafted POST request with a very long webSiteId parameter to check if the device responds abnormally or crashes.

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Mitigation Strategies

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

If possible, disable the web management interface or restrict HTTP access to prevent remote exploitation.

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

Apply any available firmware updates or patches from the vendor addressing this vulnerability.

As a temporary workaround, implement network-level filtering or intrusion prevention rules to block HTTP POST requests with abnormally long parameters targeting /goform/webtypelibrary.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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