Executive Summary

CVE-2026-3799 is a stack-based buffer overflow vulnerability found in the Tenda i3 router firmware version 1.0.0.6(2204). It specifically affects the formSetCfm function in the /goform/setcfm endpoint, where the funcpara1 parameter is not properly validated for length.

An attacker can exploit this vulnerability remotely by sending a specially crafted HTTP POST request with an excessively long string in the funcpara1 parameter, causing a buffer overflow on the stack.

This overflow can lead to denial of service or potentially allow arbitrary code execution on the affected device.

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring for HTTP POST requests sent to the /goform/setcfm endpoint with an unusually long or excessively large payload in the funcpara1 parameter.'}, {'type': 'paragraph', 'content': 'A practical detection method is to capture network traffic and filter for POST requests targeting /goform/setcfm, then inspect the length of the funcpara1 parameter.'}, {'type': 'list_item', 'content': 'Use a network packet capture tool like tcpdump or Wireshark to capture HTTP traffic.'}, {'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': 'Use curl or similar tools to test the endpoint by sending a POST request with a large payload in funcpara1 to see if the device responds abnormally or crashes.'}, {'type': 'list_item', 'content': 'Example curl command to test: curl -X POST http://<target-ip>/goform/setcfm -d \'funcpara1=$(python3 -c "print(\'a\'*10000)")\''}] [1, 2]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'Currently, there are no known countermeasures or official patches available for this vulnerability.'}, {'type': 'paragraph', 'content': "Immediate mitigation steps include limiting access to the affected device's management interface, especially restricting remote access to the /goform/setcfm endpoint."}, {'type': 'paragraph', 'content': 'Consider implementing network-level protections such as firewall rules to block suspicious POST requests targeting /goform/setcfm.'}, {'type': 'paragraph', 'content': 'Monitor the device for unusual behavior or crashes that may indicate exploitation attempts.'}, {'type': 'paragraph', 'content': 'Ultimately, it is recommended to replace the affected Tenda i3 device with a secure alternative as no patches are currently available.'}] [3]

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Impact Analysis

Exploitation of this vulnerability can lead to serious impacts including denial of service (DoS), which would disrupt the normal operation of the Tenda i3 router.

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

Such control could compromise the confidentiality, integrity, and availability of the network traffic and devices connected through the router.

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Compliance Impact

I don't know

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