CVE-2026-6199: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-6199 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda F456 router firmware version 1.0.0.5. The vulnerability exists in the fromqossetting function within the /goform/qossetting endpoint, where improper handling of the page argument allows attackers to trigger a buffer overflow condition. This vulnerability can be exploited remotely over the network, potentially leading to device compromise or denial of service.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash affected Tenda F456 routers, compromising network infrastructure security.

Affected Products

• Tenda F456 firmware version 1.0.0.5
• Tenda F456 routers running vulnerable firmware builds
• Network environments with exposed Tenda F456 management interfaces

Discovery Timeline

• April 13, 2026 - CVE-2026-6199 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6199

Vulnerability Analysis

This vulnerability falls under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which describes vulnerabilities where software performs operations on a memory buffer without properly validating that the read/write operations stay within the intended boundaries.

The vulnerable function fromqossetting processes user-supplied input from the page argument without adequate bounds checking. When a specially crafted request is sent to the /goform/qossetting endpoint, the oversized input causes a stack-based buffer overflow. This memory corruption condition occurs because the function allocates a fixed-size buffer on the stack but fails to validate that the incoming data fits within this allocation.

The network-accessible attack vector with low complexity requirements means that exploitation can be achieved without authentication, making this a significant risk for exposed devices. Successful exploitation could allow an attacker to overwrite critical stack data, including return addresses, potentially leading to arbitrary code execution in the context of the web server process.

Root Cause

The root cause of this vulnerability is insufficient input validation in the fromqossetting function. The function accepts the page parameter from HTTP requests processed by the /goform/qossetting handler but fails to properly validate the length of this input before copying it into a fixed-size stack buffer. This classic buffer overflow pattern allows data to overflow beyond the allocated buffer boundaries, corrupting adjacent memory on the stack.

Attack Vector

The vulnerability can be exploited remotely via the network by sending a malicious HTTP request to the router's web management interface. An attacker would craft a request to the /goform/qossetting endpoint with an oversized page parameter value designed to overflow the stack buffer. The attack does not require any special privileges beyond network access to the router's management interface, though it does require low-level authentication access based on the vulnerability characteristics.

The exploitation of this vulnerability has been publicly disclosed. For detailed technical analysis, refer to the GitHub Vulnerability Report which contains the proof-of-concept details.

Detection Methods for CVE-2026-6199

Indicators of Compromise

• Unusual or malformed HTTP POST requests to the /goform/qossetting endpoint containing oversized page parameter values
• Router crashes or unexpected reboots that may indicate exploitation attempts
• Anomalous outbound network traffic from the router suggesting potential compromise
• Web server error logs showing buffer-related crashes or segmentation faults

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests to /goform/qossetting with abnormally large parameter values
• Deploy web application firewall (WAF) rules to block requests exceeding expected parameter lengths for the affected endpoint
• Monitor router system logs for segmentation faults or crash dumps related to the web server process
• Utilize SentinelOne Singularity to detect anomalous behavior patterns on network infrastructure devices

Monitoring Recommendations

• Enable logging for all HTTP requests to router administration interfaces and review for suspicious patterns
• Set up alerts for router restarts or service crashes that could indicate active exploitation
• Monitor network traffic for unusual data transfers originating from router management interfaces
• Implement baseline monitoring for router process behavior to detect code execution anomalies

How to Mitigate CVE-2026-6199

Immediate Actions Required

• Restrict access to the Tenda F456 web management interface to trusted internal networks only using firewall rules
• Disable remote management access from WAN interfaces if not required
• Implement network segmentation to isolate router management interfaces from untrusted networks
• Monitor for vendor firmware updates from Tenda that address this vulnerability

Patch Information

At the time of publication, no official patch has been confirmed from Tenda. Administrators should regularly check the Tenda Official Website for firmware updates addressing this vulnerability. Additional vulnerability tracking information is available at VulDB #357121.

Workarounds

• Implement access control lists (ACLs) to restrict access to the /goform/qossetting endpoint from untrusted sources
• Place a reverse proxy or WAF in front of the router management interface to filter malicious requests
• Disable the web management interface entirely if not needed and use alternative management methods such as serial console
• Consider replacing vulnerable devices with alternative router solutions until a patch is available

# Configuration example - Restrict router management interface access via iptables on upstream firewall
# Block external access to router management port (typically port 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 only trusted management network
iptables -I FORWARD -s <trusted_network>/24 -d <router_ip> -p tcp --dport 80 -j ACCEPT