Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-3729 is a stack-based buffer overflow vulnerability found in the Tenda F453 router, version 1.0.0.3. It exists in the fromPptpUserAdd function of the /goform/PPTPDClient component. The vulnerability arises when the input parameters "username" and "opttype" are manipulated, specifically when "opttype" equals 1. In this case, a variable is passed to the sprintf function without any length validation, causing an overflow of the stack buffer.'}, {'type': 'paragraph', 'content': 'An attacker can exploit this vulnerability remotely by sending a specially crafted HTTP POST request to the /goform/PPTPDClient endpoint. This can lead to denial of service or remote code execution on the affected device.'}] [1, 2, 3]

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Impact Analysis

This vulnerability can have severe impacts including denial of service (DoS) and remote code execution (RCE) on the affected Tenda F453 router. Exploiting the buffer overflow allows an attacker to compromise the confidentiality, integrity, and availability of the device.

• Denial of Service: The device can be made unavailable by crashing the service.
• Remote Code Execution: An attacker can execute arbitrary code remotely, potentially taking full control of the device.
• Compromise of device security, leading to unauthorized access or manipulation of network traffic.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring for suspicious HTTP POST requests sent to the /goform/PPTPDClient endpoint, especially those containing unusually large or crafted "username" parameters or specific "opttype" values (such as 1) that trigger the buffer overflow.'}, {'type': 'paragraph', 'content': 'A practical detection method is to capture and analyze network traffic for POST requests targeting /goform/PPTPDClient with large payloads or unusual parameter values.'}, {'type': 'list_item', 'content': 'Use network packet capture tools like tcpdump or Wireshark to filter HTTP POST requests to /goform/PPTPDClient.'}, {'type': 'list_item', 'content': "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 -i '/goform/PPTPDClient'"}, {'type': 'list_item', 'content': 'Inspect captured HTTP POST data for large or malformed "username" parameters or "opttype=1".'}, {'type': 'paragraph', 'content': 'Additionally, checking the firmware version of the Tenda F453 router (version 1.0.0.3/3.As) can help identify if the device is vulnerable.'}] [1, 2, 3]

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Mitigation Strategies

Currently, there are no known vendor-provided patches or fixes available for this vulnerability.

Immediate mitigation steps include:

• Restrict remote access to the affected Tenda F453 router, especially blocking HTTP POST requests to the /goform/PPTPDClient endpoint.
• Implement network-level filtering or firewall rules to prevent exploitation attempts targeting this endpoint.
• Monitor network traffic for suspicious activity related to this vulnerability.
• Consider replacing the affected device with a non-vulnerable alternative to avoid exploitation.

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