CVE-2026-5043: Belkin F9k1122 Buffer Overflow Vulnerability

CVE-2026-5043 Overview

A stack-based buffer overflow vulnerability has been identified in Belkin F9K1122 wireless range extender firmware version 1.00.33. The vulnerability exists in the formSetPassword function within the /goform/formSetPassword endpoint of the Parameter Handler component. By manipulating the webpage argument, an authenticated remote attacker can trigger a stack-based buffer overflow, potentially leading to arbitrary code execution on the affected device.

Critical Impact

Remote exploitation of this stack-based buffer overflow vulnerability is possible, enabling attackers to potentially execute arbitrary code and gain full control of the affected Belkin wireless range extender device.

Affected Products

• Belkin F9K1122 Firmware version 1.00.33
• Belkin F9K1122 Hardware

Discovery Timeline

• 2026-03-29 - CVE-2026-5043 published to NVD
• 2026-03-30 - Last updated in NVD database

Technical Details for CVE-2026-5043

Vulnerability Analysis

This vulnerability is classified as both a Memory Corruption issue (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) and an Out-of-Bounds Write (CWE-787). The formSetPassword function 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 provides input that exceeds the buffer's allocated size, the excess data overwrites adjacent stack memory, including potentially the return address.

The network-accessible nature of this vulnerability makes it particularly concerning for home and small office environments where these range extenders are commonly deployed. An authenticated attacker with network access to the device's web management interface can exploit this flaw without requiring physical access to the device.

Root Cause

The root cause of this vulnerability lies in improper input validation within the formSetPassword function. The function accepts the webpage argument from HTTP form data without adequate bounds checking before storing it in a stack-allocated buffer. This classic buffer overflow pattern allows attackers to write beyond the intended memory boundaries, corrupting stack data structures.

Attack Vector

The attack is carried out remotely over the network by sending a crafted HTTP POST request to the /goform/formSetPassword endpoint. The attacker must have authenticated access to the device's web interface, which requires low-privilege credentials. The webpage parameter is manipulated to contain malicious payload data that exceeds the expected buffer size, triggering the overflow condition.

The vulnerability can be exploited by sending an oversized value in the webpage parameter to the vulnerable endpoint. This causes the stack buffer to overflow, potentially overwriting the return address and enabling arbitrary code execution. Technical details regarding this vulnerability are documented in the GitHub README on Belkin Vulnerability and VulDB Vulnerability #353966.

Detection Methods for CVE-2026-5043

Indicators of Compromise

• Unusual HTTP POST requests to /goform/formSetPassword endpoint with abnormally large webpage parameter values
• Unexpected device reboots or crashes of the Belkin F9K1122 range extender
• Anomalous network traffic originating from the range extender to external destinations
• Changes to device configuration or password settings without administrator action

Detection Strategies

• Implement network intrusion detection rules to monitor for oversized HTTP POST requests targeting /goform/formSetPassword
• Deploy web application firewall (WAF) rules to detect and block buffer overflow attempt patterns in form submissions
• Enable logging on network perimeter devices to capture suspicious traffic to IoT devices
• Use SentinelOne Singularity to monitor network segments for anomalous behavior from IoT devices

Monitoring Recommendations

• Regularly review device logs for authentication attempts and configuration changes
• Monitor network traffic patterns from the affected device for unusual outbound connections
• Implement network segmentation to isolate IoT devices from critical network infrastructure
• Set up alerts for any firmware modification attempts or unexpected device behavior

How to Mitigate CVE-2026-5043

Immediate Actions Required

• Restrict access to the device's web management interface to trusted IP addresses only
• Implement strong authentication credentials and change default passwords
• Place the affected device behind a firewall and disable remote management access from the internet
• Consider network segmentation to isolate the vulnerable device from critical systems
• Monitor the device for signs of compromise while awaiting vendor response

Patch Information

No patch is currently available from Belkin. According to the vulnerability disclosure, the vendor was contacted about this issue but did not respond. Users should monitor Belkin's support page for any future firmware updates and consider replacing the device with a supported model if security updates are not forthcoming.

Workarounds

• Disable the web management interface if not required for day-to-day operations
• Implement strict firewall rules to block external access to the device's management ports
• Use MAC address filtering and strong WPA3 encryption to limit network access
• Consider replacing the device with a currently supported model that receives security updates

# Example iptables rules to restrict access to the device management interface
# Replace 192.168.1.100 with your Belkin device IP and 192.168.1.10 with trusted admin IP

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

# Allow only trusted admin IP to access device
iptables -I FORWARD -s 192.168.1.10 -d 192.168.1.100 -p tcp --dport 80 -j ACCEPT