CVE-2026-5629: Belkin F9K1015 Buffer Overflow Vulnerability

CVE-2026-5629 Overview

A stack-based buffer overflow vulnerability has been identified in the Belkin F9K1015 wireless router firmware version 1.00.10. The vulnerability exists within the formSetFirewall function located in the /goform/formSetFirewall endpoint. By manipulating the webpage argument, an attacker can trigger a stack-based buffer overflow condition, potentially leading to arbitrary code execution on the affected device.

The exploit for this vulnerability is publicly available, significantly increasing the risk of active exploitation in the wild. Despite early notification, the vendor (Belkin) did not respond to disclosure attempts.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to execute arbitrary code on the router, potentially gaining complete control over the device and compromising the entire network segment.

Affected Products

• Belkin F9K1015 Wireless Router Firmware version 1.00.10

Discovery Timeline

• 2026-04-06 - CVE-2026-5629 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5629

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formSetFirewall function fails to properly validate the length of user-supplied input in the webpage parameter before copying it to a fixed-size stack buffer. When an attacker sends a specially crafted HTTP request with an oversized webpage argument, the function writes beyond the allocated buffer boundaries on the stack.

The network-accessible nature of this vulnerability makes it particularly dangerous, as attackers can target the router remotely without requiring physical access or prior authentication. Given the router's role as a network gateway, successful exploitation could provide attackers with a foothold to launch further attacks against devices on the internal network.

Root Cause

The root cause lies in insufficient bounds checking within the formSetFirewall function when processing the webpage parameter from HTTP POST requests. The function uses an unsafe memory copy operation that does not verify if the input data exceeds the destination buffer's capacity on the stack. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including return addresses and saved registers.

Attack Vector

The attack is executed remotely over the network by sending a malicious HTTP request to the vulnerable endpoint at /goform/formSetFirewall. The attacker crafts a request with an excessively long webpage parameter value designed to overflow the stack buffer. This overflow can overwrite the function's return address, redirecting execution flow to attacker-controlled shellcode or ROP gadgets.

The attack requires low privileges (authenticated user access to the router's web interface) but does not require user interaction. The vulnerability affects the confidentiality, integrity, and availability of the device, potentially allowing full system compromise.

For detailed technical information about this vulnerability, refer to the GitHub vulnerability disclosure and the VulDB entry.

Detection Methods for CVE-2026-5629

Indicators of Compromise

• Abnormally large HTTP POST requests targeting /goform/formSetFirewall
• Unexpected router reboots or crashes indicating potential exploitation attempts
• Unusual outbound network connections originating from the router's management interface
• Changes to firewall rules or router configuration without administrator action

Detection Strategies

• Monitor HTTP traffic to the router's web interface for POST requests to /goform/formSetFirewall with unusually large webpage parameter values
• Implement network intrusion detection rules to identify buffer overflow exploitation patterns targeting Belkin routers
• Deploy SentinelOne Singularity for IoT to identify and protect vulnerable network devices

Monitoring Recommendations

• Enable comprehensive logging on the router if supported and forward logs to a SIEM for analysis
• Monitor for anomalous traffic patterns originating from router IP addresses
• Establish baseline behavior for router management interface access and alert on deviations

How to Mitigate CVE-2026-5629

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote administration features if enabled
• 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. The vendor was contacted regarding this vulnerability but did not respond. Users should monitor VulDB and official Belkin channels for any future security updates.

Workarounds

• Configure firewall rules on upstream network devices to block external access to the router's web interface (typically port 80/443)
• Disable the web management interface entirely if not required for operations
• Use a VPN for remote management needs rather than exposing the web interface directly
• Implement strong network access controls to limit which devices can communicate with the router's management interface

# Example: Block external access to router management interface using iptables on an upstream device
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP