Executive Summary

CVE-2026-2203 is a critical buffer overflow vulnerability found in the Tenda AC8 router, version 16.03.33.05, specifically within the Embedded Httpd Service component.

The flaw exists in the handling of the /goform/fast_setting_wifi_set endpoint, where improper manipulation of the timeZone argument leads to a buffer overflow condition.

This occurs because the product copies an input buffer to an output buffer without verifying that the input size is smaller than the output buffer size, violating secure coding practices and corresponding to CWE-120 (Classic Buffer Overflow).

The vulnerability can be exploited remotely without authentication by sending a specially crafted HTTP request containing an excessively long timeZone value.

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Impact Analysis

Exploitation of this vulnerability can impact the confidentiality, integrity, and availability of the affected device.

An attacker can remotely execute the exploit to cause a denial-of-service (DoS) condition or potentially execute arbitrary code due to the buffer overflow.

Since the exploit requires no authentication and is easy to perform, it poses a significant risk to the security and stability of the device.

No known countermeasures or mitigations currently exist, so affected devices should be replaced with alternatives.

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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 requests targeting the /goform/fast_setting_wifi_set endpoint with unusually long or malformed timeZone parameters, which may indicate attempts to exploit the buffer overflow.'}, {'type': 'paragraph', 'content': 'Since the exploit involves sending a specially crafted HTTP request, network detection can involve capturing and inspecting HTTP traffic for such requests.'}, {'type': 'list_item', 'content': "Use network packet capture tools like tcpdump or Wireshark to filter HTTP requests to the vulnerable endpoint, for example: tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/fast_setting_wifi_set'"}, {'type': 'list_item', 'content': "Use curl or similar tools to test the endpoint manually by sending a request with an excessively long timeZone parameter to observe if the device responds abnormally (for detection purposes only, do not exploit in production): curl -X POST http://<device-ip>/goform/fast_setting_wifi_set -d 'timeZone=AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA'"}] [1, 3]

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Mitigation Strategies

[{'type': 'paragraph', 'content': 'There are no known countermeasures or mitigations currently available for this vulnerability.'}, {'type': 'paragraph', 'content': 'The recommended immediate step is to replace the affected Tenda AC8 device with an alternative product that is not vulnerable.'}, {'type': 'paragraph', 'content': "Additionally, restricting network access to the device's HTTP service and monitoring for exploit attempts can help reduce risk until replacement."}] [1]

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