CVE-2026-7055: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-7055 Overview

A buffer overflow vulnerability has been identified in Tenda F456 router firmware version 1.0.0.5. This security flaw affects the fromVirtualSer function within the /goform/VirtualSer endpoint of the httpd component. The vulnerability is triggered through improper handling of the menufacturer and Go arguments, allowing attackers to overflow memory buffers and potentially execute arbitrary code on affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability over the network to compromise Tenda F456 routers, potentially gaining full control of the device and using it as a pivot point for further network attacks.

Affected Products

• Tenda F456 Firmware version 1.0.0.5
• Tenda F456 Hardware

Discovery Timeline

• 2026-04-26 - CVE-2026-7055 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-7055

Vulnerability Analysis

This vulnerability falls under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromVirtualSer function in the Tenda F456 router's httpd web service fails to properly validate the length of user-supplied input for the menufacturer and Go parameters before copying them into fixed-size memory buffers.

When an attacker sends a specially crafted HTTP request to the /goform/VirtualSer endpoint with oversized values for these parameters, the function writes data beyond the allocated buffer boundaries. This memory corruption can overwrite adjacent memory regions, including critical control structures such as return addresses or function pointers.

The vulnerability is remotely exploitable without requiring user interaction, making it particularly dangerous for internet-exposed devices. An attacker with low privileges can leverage this flaw to achieve high impact on confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of this vulnerability is insufficient input validation in the fromVirtualSer function. The httpd component does not implement proper bounds checking when processing the menufacturer and Go arguments from incoming HTTP POST requests. The function copies user-controlled data directly into stack or heap buffers without verifying that the input length does not exceed the allocated buffer size, resulting in a classic buffer overflow condition.

Attack Vector

The attack vector is network-based, targeting the httpd web management interface of the Tenda F456 router. An attacker can exploit this vulnerability by:

1. Identifying a vulnerable Tenda F456 router accessible over the network
2. Crafting a malicious HTTP POST request to /goform/VirtualSer
3. Including oversized values in the menufacturer or Go parameters
4. Sending the request to trigger the buffer overflow
5. Achieving code execution or denial of service depending on the payload

The exploit has been publicly disclosed, increasing the risk of active exploitation. Technical details are available in the GitHub PoC Repository.

Detection Methods for CVE-2026-7055

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/VirtualSer with abnormally long parameter values
• Router crashes or unexpected reboots indicating possible exploitation attempts
• Unusual outbound network connections from the router to unknown IP addresses
• Modified router configurations or firmware without administrator action

Detection Strategies

• Deploy network intrusion detection rules to monitor for HTTP requests containing oversized menufacturer or Go parameters targeting /goform/VirtualSer
• Implement web application firewall rules to block requests with parameter lengths exceeding expected values
• Monitor httpd process behavior for signs of memory corruption or unexpected crashes
• Review router access logs for suspicious authentication patterns or repeated requests to the vulnerable endpoint

Monitoring Recommendations

• Enable verbose logging on the Tenda F456 web management interface if available
• Configure network monitoring to alert on traffic anomalies directed at router management ports
• Implement regular firmware integrity checks to detect unauthorized modifications
• Monitor for unusual DNS queries or network traffic patterns originating from the router

How to Mitigate CVE-2026-7055

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management if not required for operations
• Place the router behind a firewall that can filter malicious requests
• Monitor network traffic for exploitation attempts targeting the vulnerable endpoint

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Administrators should monitor the Tenda Official Website for firmware updates addressing this security issue. Additional vulnerability details can be found at VulDB Vulnerability #359628.

Workarounds

• Disable the web management interface entirely and use alternative management methods if available
• Implement strict network segmentation to isolate vulnerable devices from untrusted networks
• Configure firewall rules to block external access to the router's management ports (typically TCP 80/443)
• Consider replacing the affected device with a supported alternative if no patch becomes available

# Example iptables rules to restrict management access
# Block external access to router management interface
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

# Log potential exploitation attempts
iptables -A INPUT -p tcp --dport 80 -m string --string "/goform/VirtualSer" --algo bm -j LOG --log-prefix "CVE-2026-7055: "