CVE-2026-5610: Belkin F9K1015 Buffer Overflow Vulnerability

CVE-2026-5610 Overview

A stack-based buffer overflow vulnerability has been identified in the Belkin F9K1015 wireless router firmware version 1.00.10. The vulnerability exists in the formWISP5G function located in the /goform/formWISP5G endpoint. Improper handling of the webpage argument allows attackers to trigger a stack-based buffer overflow condition, potentially leading to remote code execution or denial of service.

The exploit has been publicly disclosed, and the vendor was contacted regarding this vulnerability but did not respond. This lack of vendor response leaves affected devices without an official patch, increasing the risk for users of this router model.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash the device, compromising network security for all connected devices.

Affected Products

• Belkin F9K1015 Wireless Router
• Firmware Version 1.00.10

Discovery Timeline

• 2026-04-06 - CVE-2026-5610 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5610

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formWISP5G function in the router's web management interface fails to properly validate the length of user-supplied input through the webpage parameter before copying it to a fixed-size stack buffer.

When an attacker sends a specially crafted HTTP request to the /goform/formWISP5G endpoint with an oversized webpage argument, the input data overwrites adjacent memory on the stack. This can corrupt return addresses, saved registers, and other critical stack data, enabling an attacker to redirect program execution flow.

The vulnerability is exploitable remotely over the network, requiring only low-level authentication privileges. No user interaction is needed for exploitation, making this a significant threat for exposed devices.

Root Cause

The root cause is improper bounds checking in the formWISP5G function. The function copies user-supplied data from the webpage HTTP parameter directly into a stack-allocated buffer without validating that the input length does not exceed the buffer's capacity. This classic buffer overflow pattern allows attackers to write beyond the intended memory boundaries.

Attack Vector

The attack is network-based and targets the router's web management interface. An authenticated attacker can send a malicious HTTP POST request to /goform/formWISP5G with an excessively long webpage parameter value. The overflow corrupts stack memory, potentially allowing:

1. Overwriting the return address to redirect execution to attacker-controlled code
2. Injecting shellcode into the stack buffer for execution
3. Causing a denial of service by crashing the router firmware

Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2026-5610

Indicators of Compromise

• Unusual HTTP POST requests targeting /goform/formWISP5G with abnormally large webpage parameter values
• Router crashes or unexpected reboots without explanation
• Unauthorized configuration changes on the affected Belkin F9K1015 device
• Network traffic anomalies originating from the router to unknown external addresses

Detection Strategies

• Monitor web server logs on network devices for requests to /goform/formWISP5G endpoints with large payloads
• Implement network intrusion detection rules to flag HTTP requests with oversized form parameters targeting Belkin router endpoints
• Deploy network monitoring to detect unusual traffic patterns from router management interfaces

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic to and from Belkin router management interfaces
• Configure alerts for HTTP requests exceeding normal parameter size thresholds directed at IoT devices
• Regularly audit network device firmware versions and compare against known vulnerable versions

How to Mitigate CVE-2026-5610

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management access if enabled on the Belkin F9K1015
• Implement network segmentation to isolate the vulnerable router from critical network assets
• Consider replacing the affected device with a supported router model that receives security updates

Patch Information

No official patch is currently available from Belkin. The vendor was contacted regarding this vulnerability but did not respond. Users should monitor the VulDB entry for any updates on vendor response or community-developed mitigations.

Workarounds

• Disable the web management interface entirely if not required for operation
• Place the router behind a firewall that blocks access to the /goform/ endpoints from untrusted networks
• Use strong authentication credentials and limit management access to specific IP addresses
• Consider deploying third-party firmware (if compatible) that may address the vulnerability

# Example: Block access to vulnerable endpoint using iptables on upstream firewall
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -m string --string "/goform/formWISP5G" --algo bm -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -m string --string "/goform/formWISP5G" --algo bm -j DROP