CVE-2026-6200: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-6200 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F456 firmware version 1.0.0.5. The vulnerability exists within the formwebtypelibrary function located in the /goform/webtypelibrary file. Remote attackers can exploit this vulnerability by manipulating the menufacturer/Go argument, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash the device, compromising network security and availability.

Affected Products

• Tenda F456 Firmware Version 1.0.0.5

Discovery Timeline

• April 13, 2026 - CVE-2026-6200 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6200

Vulnerability Analysis

This vulnerability falls under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formwebtypelibrary function in the Tenda F456 router firmware fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer. When an attacker sends a specially crafted request to the /goform/webtypelibrary endpoint with an oversized menufacturer/Go parameter, the function writes beyond the allocated buffer boundaries on the stack.

Stack-based buffer overflows in embedded devices like routers are particularly dangerous because they can allow attackers to overwrite critical stack data including return addresses. This can redirect program execution to attacker-controlled code, enabling complete device compromise. The network-accessible nature of this vulnerability means it can be exploited remotely without physical access to the device.

Root Cause

The root cause stems from improper bounds checking in the formwebtypelibrary function when processing HTTP form parameters. The function copies user-controlled input from the menufacturer/Go argument directly into a stack-allocated buffer without verifying that the input length does not exceed the buffer's capacity. This classic memory safety issue allows attackers to overflow the buffer and corrupt adjacent stack memory.

Attack Vector

The vulnerability is exploitable over the network via HTTP requests to the router's web management interface. An attacker with low-privilege access to the network can send malicious requests to the /goform/webtypelibrary endpoint. The attack does not require user interaction and can be initiated remotely. The exploit has been publicly disclosed, which increases the risk of active exploitation.

The attack flow involves:

1. Identifying a vulnerable Tenda F456 device with firmware version 1.0.0.5
2. Crafting an HTTP request to /goform/webtypelibrary with an oversized menufacturer/Go parameter
3. Sending the malicious request to trigger the buffer overflow
4. Achieving code execution or denial of service depending on payload

Detection Methods for CVE-2026-6200

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/webtypelibrary endpoint with abnormally large parameter values
• Router crashes, reboots, or unresponsive behavior following web management interface access
• Anomalous network traffic patterns originating from or directed at the Tenda F456 device
• Log entries showing repeated access attempts to form handling endpoints

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /goform/webtypelibrary with oversized parameters
• Monitor for unusual patterns of requests to Tenda device web interfaces, particularly those with large POST bodies
• Deploy SentinelOne Singularity to detect exploitation attempts and anomalous device behavior on network segments containing vulnerable devices

Monitoring Recommendations

• Enable logging on network firewalls and IDS/IPS systems to capture traffic to and from Tenda devices
• Establish baseline network behavior for IoT and router devices to identify deviations that may indicate exploitation
• Regularly review router access logs for suspicious activity patterns

How to Mitigate CVE-2026-6200

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Implement network segmentation to isolate vulnerable Tenda F456 devices from critical network assets
• Disable remote management features if not required for operations
• Apply firewall rules to block external access to router management ports

Patch Information

No official vendor patch information is currently available. Monitor the Tenda Official Website for firmware updates addressing this vulnerability. Technical details regarding this vulnerability can be found at the GitHub Vulnerability README and the VulDB Entry #357122.

Workarounds

• Restrict web management interface access to specific trusted IP addresses or network segments using access control lists
• Place vulnerable devices behind a network firewall that filters incoming requests to management endpoints
• Consider replacing affected devices with alternative hardware that receives regular security updates if patching is unavailable
• Disable the web management interface entirely if device management can be performed through other means

# Example firewall rule to restrict access to router management interface
# Block external access to common router management ports
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP