CVE-2026-6134: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6134 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda F451 routers running firmware version 1.0.0.7_cn_svn7958. This vulnerability affects the fromqossetting function located in the /goform/qossetting file. By manipulating the qos argument, an attacker can trigger a buffer overflow condition that overwrites adjacent memory on the stack, potentially leading to arbitrary code execution or device compromise.

The vulnerability is remotely exploitable over the network and requires low-privilege authentication. An exploit has been publicly released, increasing the risk of active exploitation against unpatched devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code, crash the device, or gain unauthorized control over the affected Tenda F451 router.

Affected Products

• Tenda F451 firmware version 1.0.0.7_cn_svn7958
• Tenda F451 routers with vulnerable QoS configuration endpoints
• Network environments utilizing affected Tenda router firmware

Discovery Timeline

• 2026-04-12 - CVE-2026-6134 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-6134

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which encompasses a broad category of memory safety issues. The flaw exists within the QoS (Quality of Service) settings handler in the Tenda F451 router's web management interface.

The fromqossetting function fails to properly validate the length of user-supplied input passed through the qos parameter before copying it into a fixed-size stack buffer. When an attacker provides an oversized input value, the function writes beyond the allocated buffer boundaries, corrupting adjacent stack memory including potentially the return address and saved frame pointers.

This type of vulnerability is particularly severe in embedded devices like routers, which often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization), stack canaries, or non-executable stack regions. The network-accessible nature of the vulnerability combined with the public availability of exploit code significantly elevates the risk profile.

Root Cause

The root cause of this vulnerability is insufficient input validation in the fromqossetting function when processing the qos argument. The function uses unsafe string handling operations that do not enforce proper boundary checks, allowing data to be written past the end of a stack-allocated buffer. This represents a classic stack-based buffer overflow pattern where developer oversight in bounds checking leads to exploitable memory corruption conditions.

Attack Vector

The attack can be executed remotely over the network by sending a specially crafted HTTP request to the /goform/qossetting endpoint on the vulnerable router. The attacker must have low-level authentication to the device's web interface.

The exploitation process involves:

1. Authenticating to the router's web management interface with valid credentials
2. Crafting a malicious HTTP POST request to /goform/qossetting
3. Including an oversized value in the qos parameter to trigger the overflow
4. Overwriting the return address to redirect execution flow to attacker-controlled code or shellcode

For detailed technical analysis and proof-of-concept information, refer to the GitHub Issue on CVE and VulDB entry #356998.

Detection Methods for CVE-2026-6134

Indicators of Compromise

• Unusual or repeated HTTP POST requests to /goform/qossetting with abnormally large parameter values
• Router crashes, unexpected reboots, or unresponsive web management interface
• Suspicious network traffic originating from router management ports
• Modified router configuration or unexpected firmware changes

Detection Strategies

• Deploy network intrusion detection rules to identify oversized requests to the QoS settings endpoint
• Monitor router logs for authentication attempts followed by requests to /goform/qossetting
• Implement web application firewall rules to block requests with excessively long parameter values
• Conduct regular firmware version audits to identify vulnerable Tenda F451 devices in the environment

Monitoring Recommendations

• Enable and centralize logging for all Tenda router web management interface access
• Set up alerts for multiple failed authentication attempts followed by successful logins
• Monitor for anomalous outbound traffic from router IP addresses that could indicate compromise
• Establish baseline network behavior to detect deviations indicative of exploitation attempts

How to Mitigate CVE-2026-6134

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Implement strong authentication credentials and change default passwords immediately
• Disable remote management features if not required for operations
• Segment the router management interface from untrusted network segments using firewall rules

Patch Information

At the time of publication, no official patch from Tenda has been confirmed. Network administrators should monitor the Tenda Official Site for firmware updates addressing this vulnerability. Review the VulDB submission and GitHub issue for ongoing updates regarding remediation options.

Workarounds

• Restrict web management interface access to localhost or specific trusted IP addresses only
• Place the router behind an additional firewall that blocks external access to management ports
• Consider deploying alternative router firmware if available and compatible
• Implement network-level access controls to limit who can reach the /goform/qossetting endpoint

# Example: Restrict management interface access via iptables on upstream firewall
# Block external access to router management port (typically 80/443)
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 only from trusted admin workstation
iptables -I FORWARD -s ADMIN_IP -d ROUTER_IP -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s ADMIN_IP -d ROUTER_IP -p tcp --dport 443 -j ACCEPT