Executive Summary

[{'type': 'paragraph', 'content': 'The CVE-2026-4566 vulnerability affects the Belkin F9K1122 router, specifically firmware version 1.00.33. It is a stack-based buffer overflow in the web interface\'s formWISP5G function. This function processes a user-supplied parameter called "webpage" and copies it into a fixed-size buffer without checking its length. This lack of bounds checking allows an attacker to overflow the buffer by sending a specially crafted HTTP POST request to the /goform/formWISP5G endpoint.'}, {'type': 'paragraph', 'content': 'Exploiting this vulnerability can lead to denial of service or potentially allow remote code execution on the device.'}] [1]

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Impact Analysis

This vulnerability can impact you by allowing an attacker to remotely execute arbitrary code or cause a denial of service on your Belkin F9K1122 router running firmware version 1.00.33. This could lead to loss of control over the device, disruption of network services, or unauthorized access to your network.

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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/formWISP5G endpoint on the Belkin F9K1122 router firmware version 1.00.33.'}, {'type': 'paragraph', 'content': 'Specifically, detection involves checking for unusually large or malformed payloads in the "webpage" parameter of these POST requests, which may indicate attempts to trigger the stack-based buffer overflow.'}, {'type': 'paragraph', 'content': 'A suggested command to detect such attempts using network traffic analysis tools like tcpdump or tshark could be:'}, {'type': 'list_item', 'content': "tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/goform/formWISP5G'"}, {'type': 'paragraph', 'content': 'Alternatively, using tshark to filter HTTP POST requests to the vulnerable endpoint:'}, {'type': 'list_item', 'content': 'tshark -Y \'http.request.method == "POST" and http.request.uri contains "/goform/formWISP5G"\' -T fields -e http.file_data'}, {'type': 'paragraph', 'content': 'Inspect the captured data for large or suspicious values in the "webpage" parameter that could indicate exploitation attempts.'}] [1]

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Mitigation Strategies

[{'type': 'paragraph', 'content': "Immediate mitigation steps include restricting access to the vulnerable router's web interface, especially the /goform/formWISP5G endpoint, to trusted networks only."}, {'type': 'paragraph', 'content': 'Implement network-level controls such as firewall rules to block incoming HTTP POST requests targeting /goform/formWISP5G from untrusted sources.'}, {'type': 'paragraph', 'content': 'Monitor network traffic for suspicious POST requests with large or malformed "webpage" parameters and block or alert on such activity.'}, {'type': 'paragraph', 'content': 'Since the vendor has not responded with a patch, consider isolating or replacing the affected device if possible to prevent exploitation.'}] [1]

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