CVE-2026-5628: Belkin F9K1015 Buffer Overflow Vulnerability

CVE-2026-5628 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 formSetSystemSettings function within the /goform/formSetSystemSettings endpoint of the Setting Handler component. Improper handling of the webpage argument allows attackers to trigger a stack-based buffer overflow condition, potentially leading to remote code execution.

Critical Impact

This vulnerability enables remote attackers to exploit the buffer overflow via network access with low privileges, potentially achieving full device compromise including arbitrary code execution on affected Belkin routers.

Affected Products

• Belkin F9K1015 firmware version 1.00.10
• Belkin F9K1015 devices with vulnerable Setting Handler component

Discovery Timeline

• April 6, 2026 - CVE-2026-5628 published to NVD
• April 7, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5628

Vulnerability Analysis

This vulnerability affects the web management interface of the Belkin F9K1015 router. The formSetSystemSettings function fails to properly validate the length of user-supplied input in the webpage argument before copying it to a fixed-size stack buffer. When an attacker sends a specially crafted request with an oversized webpage parameter, the function writes beyond the allocated buffer boundaries on the stack.

The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), indicating fundamental issues with memory boundary enforcement. Successful exploitation could allow an attacker to overwrite critical stack data including the return address, potentially redirecting execution flow to attacker-controlled code.

The exploit has been publicly disclosed, increasing the risk of active exploitation. According to reports, the vendor was contacted about this vulnerability but did not respond.

Root Cause

The root cause is insufficient bounds checking in the formSetSystemSettings function when processing the webpage argument. The function allocates a fixed-size buffer on the stack and copies user input without validating that the input length does not exceed the buffer capacity. This classic stack-based buffer overflow pattern allows memory corruption when input exceeds expected bounds.

Attack Vector

The attack is network-based and can be executed remotely against the router's web management interface. An attacker with network access and low-level privileges can submit a malicious HTTP request to the /goform/formSetSystemSettings endpoint containing an oversized webpage parameter.

The exploitation process typically involves:

1. Identifying a vulnerable Belkin F9K1015 device with firmware version 1.00.10
2. Crafting an HTTP POST request to /goform/formSetSystemSettings with a maliciously long webpage argument
3. The oversized input overflows the stack buffer, corrupting adjacent memory
4. By carefully constructing the overflow payload, an attacker can overwrite the return address and gain control of execution flow

For technical details and proof-of-concept information, refer to the GitHub PoC Repository and the VulDB Vulnerability Entry.

Detection Methods for CVE-2026-5628

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/formSetSystemSettings with abnormally large webpage parameters
• Router crashes or unexpected reboots following web interface access
• Unusual outbound network connections from the router to unknown external hosts
• Modified router configuration or firmware without administrator action

Detection Strategies

• Monitor web server logs for requests to /goform/formSetSystemSettings containing unusually long parameter values
• Implement network intrusion detection rules to flag HTTP requests with oversized form data targeting Belkin router endpoints
• Deploy anomaly detection for unexpected router behavior patterns such as repeated crashes or service interruptions
• Review network traffic for signs of post-exploitation activity originating from router IP addresses

Monitoring Recommendations

• Enable and regularly review router access logs for suspicious administrative activity
• Configure network monitoring tools to alert on large HTTP POST requests to IoT device management interfaces
• Implement network segmentation to isolate IoT devices and facilitate traffic analysis
• Establish baseline network behavior for routers to identify anomalous outbound connections

How to Mitigate CVE-2026-5628

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to port 80/443 on the affected device
• Consider replacing the Belkin F9K1015 with a supported device that receives security updates
• Monitor the device for signs of compromise and be prepared for incident response

Patch Information

At the time of publication, no vendor patch is available for this vulnerability. The vendor was contacted about this disclosure but did not respond. Users should consider the following alternatives:

• Check the VulDB Vulnerability Entry for updates on patch availability
• Contact Belkin support directly for firmware update guidance
• Given the lack of vendor response, consider device replacement with actively supported hardware

Workarounds

• Disable remote management features and restrict web interface access to wired LAN connections only
• Implement access control lists (ACLs) on upstream network devices to limit who can access the router's management interface
• Place the vulnerable router behind a firewall that can filter and inspect traffic to the management interface
• Consider deploying a third-party firewall or IPS solution to monitor and block exploitation attempts

# Example firewall rule to restrict management interface access
# Block external access to router management port (adjust IP as needed)
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

# Allow only specific trusted IP for management
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT