CVE-2026-5043 Overview
CVE-2026-5043 is a stack-based buffer overflow in the Belkin F9K1122 wireless router running firmware version 1.00.33. The flaw resides in the formSetPassword function within /goform/formSetPassword, which belongs to the device's Parameter Handler component. Attackers can trigger the overflow by manipulating the webpage argument over the network. Remote exploitation is feasible and a public exploit has been disclosed. The vendor was contacted before disclosure but did not respond, leaving affected devices without an official fix.
Critical Impact
Remote attackers with low-privileged authenticated access can corrupt the router's stack, potentially achieving arbitrary code execution and full device compromise.
Affected Products
- Belkin F9K1122 router (hardware)
- Belkin F9K1122 firmware version 1.00.33
- Deployments exposing the /goform/formSetPassword web interface
Discovery Timeline
- 2026-03-29 - CVE-2026-5043 published to the National Vulnerability Database (NVD)
- 2026-03-30 - Last updated in NVD database
Technical Details for CVE-2026-5043
Vulnerability Analysis
The vulnerability is a stack-based buffer overflow [CWE-121] tied to an out-of-bounds write [CWE-787] and a broader memory boundary handling weakness [CWE-119]. The formSetPassword handler accepts the webpage request parameter and copies its contents into a fixed-size stack buffer without enforcing length checks. When the supplied value exceeds the buffer capacity, adjacent stack memory, including saved return addresses, is overwritten.
Exploitation requires network reachability to the router's HTTP management interface. Successful exploitation can lead to denial of service, arbitrary code execution within the router's web server process, and persistent control of the device by an unauthenticated or low-privileged attacker on the network.
Root Cause
The root cause is missing input validation in the formSetPassword parameter handler. The function uses unsafe string copy semantics on the webpage argument, which is attacker-controlled and unbounded. Without length validation or use of bounded copy routines, the firmware allows the call stack to be corrupted directly from user-supplied HTTP input.
Attack Vector
An attacker sends a crafted HTTP request to /goform/formSetPassword with an oversized webpage parameter. Because the management web service runs with high privileges on the embedded operating system, a successful overflow can hijack control flow inside the router. Public exploit details are referenced in the GitHub Vulnerability Repository and the VulDB Vulnerability Detail #353966.
No verified proof-of-concept code is reproduced here. See the linked advisories for technical reproduction details.
Detection Methods for CVE-2026-5043
Indicators of Compromise
- Unusually long webpage parameter values in HTTP POST requests to /goform/formSetPassword.
- Unexpected reboots, crashes, or watchdog resets of the Belkin F9K1122 web management service.
- New or unexpected outbound connections originating from the router's management IP.
- Configuration changes to administrative credentials or remote management settings that were not initiated by an administrator.
Detection Strategies
- Inspect HTTP traffic destined for the router's admin interface and alert on webpage parameter lengths that exceed reasonable bounds (for example, more than 256 bytes).
- Deploy network IDS/IPS signatures that flag oversized POST bodies sent to /goform/formSetPassword endpoints on Belkin devices.
- Correlate router crash telemetry with management plane HTTP activity to surface attempted exploitation.
Monitoring Recommendations
- Forward router syslog and authentication events to a centralized logging platform for retention and analysis.
- Monitor for repeated failed or malformed requests to /goform/* endpoints across the network.
- Track device firmware versions in inventory and alert when F9K1122 devices running firmware 1.00.33 appear on the network.
How to Mitigate CVE-2026-5043
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal hosts only, and disable WAN-side remote administration.
- Place vulnerable F9K1122 devices behind a firewall that blocks untrusted access to TCP ports used by the admin web server.
- Inventory all Belkin F9K1122 devices on firmware 1.00.33 and prioritize replacement, since the vendor has not responded to the disclosure.
Patch Information
No vendor patch is available. According to the disclosure, Belkin was contacted but did not respond. Until an official firmware update is released, operators should treat the device as end-of-support for security purposes and plan migration to a supported router platform.
Workarounds
- Disable remote administration and any port-forwarding rules that expose the admin interface to the internet.
- Segment the router's management plane onto a dedicated VLAN accessible only to administrators.
- Use strong, unique administrative credentials to limit the population of users who can reach the authenticated portion of the web UI.
- Replace affected F9K1122 hardware with a vendor-supported router model that receives security updates.
# Configuration example: block external access to the router admin web interface
# Example iptables rule applied on an upstream firewall (adjust ROUTER_IP and interfaces)
iptables -A FORWARD -i wan0 -d ROUTER_IP -p tcp --dport 80 -j DROP
iptables -A FORWARD -i wan0 -d ROUTER_IP -p tcp --dport 443 -j DROP
# Restrict LAN-side admin access to a management subnet only
iptables -A FORWARD -s 10.10.10.0/24 -d ROUTER_IP -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d ROUTER_IP -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
