CVE-2026-7100: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-7100 Overview

A buffer overflow vulnerability has been identified in the Tenda F456 router firmware version 1.0.0.5. The vulnerability exists within the fromNatlimitof function located in the /goform/Natlimit endpoint of the httpd component. Successful exploitation of this vulnerability allows remote attackers to trigger a buffer overflow condition through crafted network requests, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially execute arbitrary code or crash the affected Tenda F456 router, compromising network security and availability.

Affected Products

• Tenda F456 Firmware version 1.0.0.5
• Tenda F456 Hardware Device

Discovery Timeline

• 2026-04-27 - CVE-2026-7100 published to NVD
• 2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-7100

Vulnerability Analysis

This buffer overflow vulnerability (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) affects the web management interface of the Tenda F456 router. The vulnerable fromNatlimitof function in the httpd service fails to properly validate the length of user-supplied input before copying it into a fixed-size memory buffer. When an attacker sends a specially crafted HTTP request to the /goform/Natlimit endpoint, the function processes the malicious input without adequate boundary checks, resulting in a buffer overflow condition.

The attack can be launched remotely over the network without requiring user interaction, though authentication credentials may be needed depending on the router's configuration. The vulnerability affects confidentiality, integrity, and availability of the device, as successful exploitation could allow attackers to execute arbitrary code with elevated privileges on the affected router.

Root Cause

The root cause of this vulnerability is improper input validation in the fromNatlimitof function. The function does not adequately verify the size of incoming data before performing memory copy operations, allowing an attacker to write data beyond the allocated buffer boundaries. This is a classic CWE-119 vulnerability where operations are not properly constrained within the bounds of the memory buffer.

Attack Vector

The attack vector is network-based, targeting the httpd service running on the Tenda F456 router. An attacker can craft malicious HTTP requests directed at the /goform/Natlimit endpoint to trigger the buffer overflow. The exploit has been publicly disclosed and a proof-of-concept is available, increasing the risk of exploitation in the wild. Attackers with network access to the router's management interface can potentially leverage this vulnerability to gain control of the device.

Technical details regarding the exploitation methodology can be found in the GitHub PoC Repository and additional context is available through the VulDB entry.

Detection Methods for CVE-2026-7100

Indicators of Compromise

• Unusual HTTP POST requests to /goform/Natlimit with oversized or malformed parameters
• Router crashes or unexpected reboots following network activity
• Abnormal memory utilization patterns on the Tenda F456 device
• Unexpected network connections originating from the router to external IP addresses

Detection Strategies

• Monitor network traffic for HTTP requests targeting the /goform/Natlimit endpoint with anomalous payload sizes
• Implement intrusion detection signatures to identify buffer overflow exploitation attempts against Tenda devices
• Deploy network segmentation to isolate IoT devices like routers from critical network segments
• Enable logging on upstream firewalls to capture suspicious traffic directed at router management interfaces

Monitoring Recommendations

• Review router access logs for repeated or unusual requests to web management endpoints
• Monitor for firmware integrity changes or unauthorized configuration modifications
• Set up alerts for router service restarts or system instability indicators
• Implement network behavior analysis to detect lateral movement following potential router compromise

How to Mitigate CVE-2026-7100

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management access if not required for operations
• Implement network segmentation to limit exposure of vulnerable devices
• Monitor network traffic for exploitation attempts targeting /goform/Natlimit

Patch Information

At the time of publication, no official security patch has been released by Tenda for this vulnerability. Network administrators should monitor the Tenda Official Website for firmware updates that address CVE-2026-7100. Additionally, consult the VulDB entry for the latest remediation information.

Workarounds

• Configure access control lists (ACLs) on upstream network devices to block external access to the router management interface
• Place the vulnerable router behind a firewall that filters malicious HTTP requests
• Consider replacing the affected device with an alternative router if a patch is not made available in a timely manner
• Implement a Web Application Firewall (WAF) capable of detecting and blocking buffer overflow attempts

# Example: Restrict management interface access using iptables on upstream device
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP
# Allow management access only from trusted admin subnet
iptables -I FORWARD -s <admin_subnet> -d <router_ip> -p tcp --dport 80 -j ACCEPT