CVE-2026-5044: Belkin F9K1122 Buffer Overflow Vulnerability

CVE-2026-5044 Overview

A stack-based buffer overflow vulnerability has been identified in the Belkin F9K1122 wireless range extender firmware version 1.00.33. This vulnerability exists in the formSetSystemSettings function within the /goform/formSetSystemSettings endpoint of the Setting Handler component. Attackers can exploit this flaw by manipulating the webpage argument, leading to memory corruption that could enable remote code execution on affected devices.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to potentially execute arbitrary code, compromise device integrity, and gain unauthorized access to network infrastructure. The exploit has been publicly disclosed and the vendor has not responded to disclosure attempts.

Affected Products

• Belkin F9K1122 Firmware version 1.00.33
• Belkin F9K1122 Hardware Device

Discovery Timeline

• 2026-03-29 - CVE-2026-5044 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-5044

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the firmware's web management interface, specifically in how the formSetSystemSettings function processes user-supplied input through the webpage parameter.

When the Setting Handler receives a crafted request containing an oversized or malformed webpage argument, the function fails to properly validate the input length before copying data to a fixed-size stack buffer. This boundary check failure allows an attacker to overwrite adjacent memory on the stack, potentially corrupting return addresses and enabling control flow hijacking.

The network-accessible nature of this vulnerability combined with the low attack complexity makes it particularly dangerous in home and small office network environments where these devices are commonly deployed.

Root Cause

The root cause of CVE-2026-5044 is improper input validation and lack of bounds checking in the formSetSystemSettings function. The firmware fails to verify the length of the webpage argument before copying it to a stack-allocated buffer. This classic memory safety issue allows attackers to write beyond the intended buffer boundaries, corrupting adjacent stack memory including saved return addresses and frame pointers.

Attack Vector

The attack vector for this vulnerability is network-based, requiring no user interaction. An authenticated attacker with low-level privileges can send a specially crafted HTTP request to the /goform/formSetSystemSettings endpoint on the device's web management interface. The malicious request includes an oversized webpage parameter designed to overflow the stack buffer.

Upon successful exploitation, the attacker can overwrite the function's return address, redirecting execution flow to attacker-controlled code. This can result in complete device compromise, including the ability to execute arbitrary commands, modify device configuration, intercept network traffic, or use the compromised device as a pivot point for further attacks within the network.

For technical details on the exploitation mechanism, refer to the GitHub Vulnerability Documentation.

Detection Methods for CVE-2026-5044

Indicators of Compromise

• Unusual HTTP POST requests to /goform/formSetSystemSettings with abnormally large webpage parameter values
• Unexpected device reboots or crashes of the Belkin F9K1122 device
• Modified device configuration settings without administrator action
• Anomalous outbound network connections from the affected device

Detection Strategies

• Deploy network intrusion detection rules to monitor for oversized HTTP parameters in requests to Belkin device management endpoints
• Implement web application firewall rules to block requests with webpage parameters exceeding expected length thresholds
• Monitor device logs for repeated authentication attempts followed by configuration change requests
• Use network traffic analysis to identify patterns consistent with buffer overflow exploitation attempts

Monitoring Recommendations

• Enable and regularly review device access logs for the Belkin F9K1122 web interface
• Configure network monitoring to alert on traffic anomalies to and from the device's management interface
• Implement network segmentation to isolate IoT devices from critical network assets
• Conduct periodic firmware integrity checks where possible

How to Mitigate CVE-2026-5044

Immediate Actions Required

• Restrict network access to the device's web management interface using firewall rules
• Disable remote management if not required and limit access to the local network only
• Implement strong authentication and change default credentials on the device
• Consider replacing the device with a supported alternative if no patch becomes available
• Segment the network to isolate the affected device from sensitive systems

Patch Information

No patch is currently available from Belkin. According to the vulnerability disclosure, the vendor was contacted but did not respond. Users should monitor VulDB Vulnerability Details and Belkin's official support channels for any future security updates.

Workarounds

• Disable the web management interface entirely if device administration is not required
• Place the device behind a firewall that blocks external access to the management ports
• Use VPN or similar secure tunneling for remote management needs instead of direct exposure
• Implement access control lists (ACLs) to restrict which IP addresses can reach the device's web interface
• Consider network-level intrusion prevention systems to block exploitation attempts

# Example iptables rules to restrict access to device management interface
# Replace 192.168.1.100 with your Belkin F9K1122 IP address
# Replace 192.168.1.0/24 with your trusted management subnet

# Block external access to web management port
iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.100 -p tcp --dport 443 -j DROP

# Allow only trusted subnet to access management interface
iptables -I FORWARD -s 192.168.1.0/24 -d 192.168.1.100 -p tcp --dport 80 -j ACCEPT