CVE-2026-6136: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6136 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F451 routers running firmware version 1.0.0.7_cn_svn7958. The vulnerability exists in the frmL7ImForm function located in the /goform/L7Im endpoint. By manipulating the page argument, an attacker can trigger a stack-based buffer overflow condition that could lead to remote code execution or denial of service on affected devices.

Critical Impact

This remotely exploitable vulnerability allows attackers with low privileges to potentially execute arbitrary code or crash affected Tenda F451 routers, compromising network infrastructure security.

Affected Products

• Tenda F451 Firmware version 1.0.0.7_cn_svn7958

Discovery Timeline

• April 13, 2026 - CVE-2026-6136 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6136

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The frmL7ImForm function in the Tenda F451 router firmware fails to properly validate the length of user-supplied input through the page parameter before copying it into a fixed-size stack buffer. When an attacker sends a specially crafted HTTP request to the /goform/L7Im endpoint with an oversized page argument, the function writes beyond the allocated buffer boundary on the stack.

The attack can be initiated remotely over the network and requires only low-level authentication privileges. Successful exploitation could allow an attacker to overwrite the return address on the stack, potentially redirecting execution flow to attacker-controlled code. This could result in full device compromise, including persistent backdoor installation, network traffic interception, or using the router as a pivot point for further attacks within the network.

Root Cause

The root cause of this vulnerability is insufficient input validation in the frmL7ImForm function. The code does not properly check the length of the page parameter before performing memory copy operations, allowing user-controlled data to overflow the stack buffer boundaries. This is a classic buffer overflow scenario common in embedded device firmware where memory-safe programming practices are not consistently applied.

Attack Vector

The vulnerability is exploitable remotely via the network. An attacker can send a malicious HTTP POST request to the /goform/L7Im endpoint on the router's web management interface. By crafting a page parameter with excessive length, the attacker triggers the stack-based buffer overflow in the frmL7ImForm function.

The attack flow involves sending an HTTP request to the vulnerable endpoint with a malformed page parameter that exceeds the expected buffer size. The vulnerable function copies this input into a fixed-size stack buffer without bounds checking, causing the overflow. The attacker can carefully craft the payload to overwrite the return address and gain control of program execution.

For technical details and proof-of-concept information, refer to the GitHub Issue Tracker and VulDB entry #357000.

Detection Methods for CVE-2026-6136

Indicators of Compromise

• Unusual HTTP POST requests targeting /goform/L7Im with abnormally large page parameter values
• Router crashes or unexpected reboots following web interface access attempts
• Anomalous network traffic patterns originating from the router's management interface
• Modified firmware or configuration files on the affected device

Detection Strategies

• Monitor HTTP traffic to Tenda router management interfaces for requests containing oversized parameters in the /goform/L7Im endpoint
• Implement intrusion detection rules to flag HTTP requests with page parameters exceeding normal length thresholds
• Deploy network monitoring to detect potential buffer overflow exploitation attempts targeting embedded devices

Monitoring Recommendations

• Enable logging on network firewalls and IDS/IPS systems to capture traffic destined for router management interfaces
• Regularly review router access logs for suspicious request patterns or repeated failed access attempts
• Monitor for unexpected device behavior such as service disruptions or configuration changes

How to Mitigate CVE-2026-6136

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management access if not strictly required
• Place affected Tenda F451 routers behind a properly configured firewall that limits access to management interfaces
• Consider network segmentation to isolate vulnerable devices from critical network assets

Patch Information

As of the last update on April 13, 2026, no official patch has been released by Tenda for this vulnerability. Administrators should monitor the Tenda Official Website for firmware updates and apply patches as soon as they become available. Additional vulnerability tracking information is available through VulDB Submission #792880.

Workarounds

• Implement access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Use a VPN to secure remote management access instead of exposing the web interface directly
• Consider replacing affected devices with alternatives that have active security support if patches are not forthcoming
• Deploy a web application firewall (WAF) in front of management interfaces to filter malicious requests

# Example: Restrict management interface access using firewall rules
# Block external access to the router management port (typically 80/443)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP