Executive Summary

CVE-2026-3972 is a stack-based buffer overflow vulnerability found in the Tenda W3 router, version 1.0.0.3(2204). It exists in the HTTP handler component, specifically in the formSetCfm function accessed via the /goform/setcfm endpoint.

The vulnerability arises from improper handling of the POST parameter funcpara1, which is copied into a fixed-length buffer on the stack without proper bounds checking. By sending a specially crafted POST request with an excessively long funcpara1 value, an attacker can cause a buffer overflow.

This overflow can overwrite the stack, including the return address, potentially leading to a crash or arbitrary code execution on the device.

The attack can only be performed from within the local network and does not require authentication.

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Impact Analysis

Exploitation of this vulnerability can compromise the confidentiality, integrity, and availability of the affected Tenda W3 router.

• An attacker on the local network can cause a denial of service by crashing the device.
• More critically, the attacker may achieve arbitrary code execution, potentially taking full control of the router.
• Since the vulnerability requires no authentication, it is relatively easy to exploit if an attacker has local network access.

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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 POST requests to the /goform/setcfm endpoint on the Tenda W3 router, specifically those containing an excessively long funcpara1 parameter.'}, {'type': 'paragraph', 'content': 'A detection method involves capturing network traffic on the local network and filtering for POST requests targeting /goform/setcfm with unusually large payloads in the funcpara1 parameter.'}, {'type': 'list_item', 'content': 'Use a network packet capture tool like tcpdump or Wireshark to capture HTTP POST requests to /goform/setcfm.'}, {'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/setcfm'"}, {'type': 'list_item', 'content': 'Analyze captured HTTP POST data for the presence of the funcpara1 parameter with an unusually long string value.'}, {'type': 'list_item', 'content': 'Alternatively, use intrusion detection systems (IDS) or web application firewalls (WAF) to create rules that alert on POST requests to /goform/setcfm with large funcpara1 parameters.'}] [1, 3]

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Mitigation Strategies

[{'type': 'paragraph', 'content': "Immediate mitigation steps include restricting access to the affected Tenda W3 router's management interface to trusted local network users only, as exploitation requires local network access."}, {'type': 'paragraph', 'content': 'Since no known countermeasures or patches are currently available, it is recommended to replace the affected device with a secure alternative.'}, {'type': 'paragraph', 'content': "Additionally, monitor network traffic for suspicious POST requests to /goform/setcfm and consider implementing network segmentation or firewall rules to limit access to the router's HTTP management interface."}] [2]

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