Executive Summary

This vulnerability is a stack-based buffer overflow found in the Tenda W20E router's web management interface, specifically in the modifyWifiFilterRules function accessed via the /goform/modifyWifiFilterRules endpoint.

It occurs when a maliciously crafted, overly long string is sent in the wifiFilterListRemark parameter, which is improperly handled by the sprintf function, leading to memory corruption.

This flaw allows an attacker to remotely trigger the overflow by sending a specially crafted HTTP POST request, potentially causing the web service to crash or enabling remote code execution.

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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 remote exploitation.

Additionally, monitoring and filtering incoming HTTP POST requests to the /goform/modifyWifiFilterRules endpoint can help detect and block malicious attempts.

If possible, disable remote management features temporarily until a patch or firmware update addressing this vulnerability is applied.

Applying any available firmware updates from the vendor that fix this vulnerability is the most effective long-term mitigation.

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Compliance Impact

The vulnerability in the Tenda W20E router's web management interface allows remote attackers to cause a stack-based buffer overflow, potentially leading to Denial of Service or Remote Code Execution.

Such a vulnerability could impact compliance with standards like GDPR or HIPAA by exposing the device to unauthorized access or disruption, which may lead to unauthorized disclosure, alteration, or loss of sensitive data.

However, the provided information does not explicitly detail the direct effects on compliance with these regulations.

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Impact Analysis

Exploitation of this vulnerability can lead to a Denial of Service (DoS) by crashing the router's web management interface, making the device unavailable or unmanageable.

More severely, it may allow an attacker to execute arbitrary code remotely on the affected device, potentially gaining control over the router.

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Detection Guidance

This vulnerability can be detected by monitoring HTTP POST requests sent to the /goform/modifyWifiFilterRules endpoint on the Tenda W20E router's web management interface.

Specifically, detection involves checking for unusually long or malformed values in the wifiFilterListRemark parameter, as exploitation involves sending an overly long string (e.g., a payload of 1000 'A' characters) to trigger the stack-based buffer overflow.

A practical approach is to capture and analyze network traffic targeting the router's web interface, looking for POST requests to /goform/modifyWifiFilterRules with suspiciously large wifiFilterListRemark values.

Example commands to detect such attempts might include using tools like tcpdump or tshark to filter HTTP POST requests to the vulnerable endpoint, for instance:

• tcpdump -i <interface> -A -s 0 'tcp port 80 and (((ip dst <router_ip>) and (tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354)))'
• tshark -i <interface> -Y 'http.request.method == "POST" and http.request.uri contains "/goform/modifyWifiFilterRules"' -T fields -e http.file_data

These commands help capture POST requests to the vulnerable endpoint, allowing inspection of the wifiFilterListRemark parameter for suspiciously long or malformed input.

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