Belkin F9K1122 Stack-Based Buffer Overflow Vulnerability

A stack-based buffer overflow vulnerability, identified as CVE-2026-5608, affects Belkin F9K1122 router version 1.00.33. The vulnerability resides within the formWlanSetup function of the /goform/formWlanSetup file. A remote attacker can exploit this vulnerability by manipulating the webpage argument, leading to arbitrary code execution on the device. This vulnerability is particularly critical because a public exploit is available, increasing the likelihood of widespread exploitation. The vendor has not responded to disclosure attempts, further compounding the risk. Successful exploitation could compromise the device’s functionality and potentially allow the attacker to gain control of the network.

Attack Chain

1. The attacker identifies a vulnerable Belkin F9K1122 router running firmware version 1.00.33.
2. The attacker sends a crafted HTTP request to the /goform/formWlanSetup endpoint.
3. The HTTP request includes a malicious payload within the webpage argument, designed to overflow the stack buffer.
4. The formWlanSetup function processes the request without proper bounds checking on the webpage argument.
5. The overflow overwrites critical data on the stack, including the return address.
6. Upon function return, control is redirected to the attacker’s injected code.
7. The attacker’s code executes with the privileges of the web server process.
8. The attacker gains control of the device and can execute arbitrary commands or modify router settings.

Impact

Successful exploitation of CVE-2026-5608 can lead to complete compromise of the affected Belkin F9K1122 router. An attacker could potentially gain unauthorized access to the network, intercept or modify network traffic, or use the compromised device as a point of entry for further attacks on other devices on the network. Given the availability of a public exploit, a large number of Belkin F9K1122 devices are at risk.

Recommendation

• Deploy the Sigma rule Detect Belkin F9K1122 Buffer Overflow Attempt to identify exploitation attempts in web server logs.
• Monitor web server logs for suspicious POST requests to /goform/formWlanSetup with unusually long webpage arguments to identify potential exploitation attempts.
• Since there is no patch available, network segmentation should be implemented to limit the impact of a compromised device, particularly for vulnerable Belkin F9K1122 routers.