Stack-Based Buffer Overflow in Tenda F451 Web Management Interface

Executive Summary

This vulnerability is a stack-based buffer overflow found in the web management interface of the Tenda F451 router, specifically in the fromNatlimit function of the /goform/Natlimit endpoint.

It occurs when a maliciously crafted, overly long string is sent as the page parameter. The vulnerability arises because the function uses the sprintf function unsafely, copying user input into a fixed-size stack buffer without proper validation.

This flaw can be exploited remotely by an attacker to cause a denial of service or potentially execute arbitrary code on the device.

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Impact Analysis

Exploitation of this vulnerability can lead to serious impacts including denial of service (DoS), where the router becomes unresponsive or crashes.

More critically, it can allow remote code execution (RCE), enabling an attacker to run arbitrary code on the affected device, potentially taking full control of the router.

This could compromise the security and integrity of your network, allowing attackers to intercept, modify, or disrupt network traffic.

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Detection Guidance

This vulnerability can be detected by sending a specially crafted HTTP request to the /goform/Natlimit endpoint of the Tenda F451 router's web management interface. The detection involves checking if the device improperly handles an overly long string in the page parameter, which triggers the stack-based buffer overflow.

A practical approach is to use a script or command that sends a large payload to the page parameter and observes the response or behavior of the device.

• Use curl or similar tools to send a long string in the page parameter, for example: curl -X POST 'http://<router-ip>/goform/Natlimit' -d 'page=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'
• Monitor the device for crashes, reboots, or abnormal behavior after sending the request, which indicates the presence of the vulnerability.

Additionally, a proof-of-concept Python script is available that automates this detection by sending a large payload to the vulnerable parameter.

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Mitigation Strategies

Immediate mitigation steps include restricting access to the web management interface of the Tenda F451 router to trusted networks or IP addresses only.

Avoid exposing the router's management interface to the internet or untrusted networks to reduce the risk of remote exploitation.

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

Check for firmware updates or patches from the vendor that address this vulnerability and apply them as soon as they become available.

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