CVE-2026-4534: Tenda FH451 Buffer Overflow Vulnerability

CVE-2026-4534 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda FH451 router firmware version 1.0.0.9. This vulnerability affects the formWrlExtraSet function within the /goform/WrlExtraSet endpoint. By manipulating the GO argument, an attacker can trigger a stack-based buffer overflow condition. The vulnerability is remotely exploitable and proof-of-concept exploit code has been published, increasing the risk of active exploitation in the wild.

Critical Impact

Remote attackers can exploit this buffer overflow to potentially execute arbitrary code or cause denial of service on affected Tenda FH451 routers, compromising network infrastructure security.

Affected Products

• Tenda FH451 Firmware Version 1.0.0.9

Discovery Timeline

• 2026-03-22 - CVE-2026-4534 published to NVD
• 2026-03-23 - Last updated in NVD database

Technical Details for CVE-2026-4534

Vulnerability Analysis

This vulnerability represents a classic stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) in embedded router firmware. The formWrlExtraSet function processes user-supplied input from the GO parameter without adequate bounds checking, allowing an attacker to write beyond the allocated stack buffer boundaries.

The vulnerability is accessible remotely through the router's web management interface at /goform/WrlExtraSet. Since this endpoint handles wireless configuration settings, it is typically accessible to authenticated users on the local network, though authentication requirements may vary depending on router configuration.

Successful exploitation could allow an attacker to overwrite critical stack data including return addresses, enabling arbitrary code execution with the privileges of the web server process running on the router. Given that embedded devices often run with elevated privileges and lack modern memory protections like ASLR or stack canaries, exploitation likelihood is increased.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and bounds checking within the formWrlExtraSet function. When processing the GO argument, the function copies user-supplied data into a fixed-size stack buffer without verifying that the input length does not exceed the buffer's capacity. This classic programming error allows attackers to supply oversized input that corrupts adjacent stack memory.

Attack Vector

The attack is initiated remotely via HTTP requests to the router's web interface. An attacker crafts a malicious HTTP POST request to /goform/WrlExtraSet with an oversized GO parameter value. The malicious payload overwrites the stack beyond the intended buffer boundaries, potentially corrupting saved registers and return addresses.

The vulnerability requires network access to the router's management interface. If the management interface is exposed to untrusted networks or the internet, the attack surface significantly expands. The attacker can leverage this overflow to hijack program execution flow, potentially achieving remote code execution on the affected device.

Technical details and proof-of-concept information can be found in the GitHub Vulnerability Repository and VulDB entry #352322.

Detection Methods for CVE-2026-4534

Indicators of Compromise

• Unusual HTTP POST requests to /goform/WrlExtraSet with abnormally large GO parameter values
• Router crashes or unexpected reboots that may indicate exploitation attempts
• Anomalous outbound network connections from the router to unknown external hosts
• Unexpected changes to router configuration or firmware

Detection Strategies

• Monitor HTTP traffic to router management interfaces for requests containing oversized parameters targeting /goform/WrlExtraSet
• Implement network intrusion detection rules to flag HTTP requests with payloads exceeding normal parameter lengths for Tenda router endpoints
• Deploy application-layer firewalls capable of inspecting and blocking malformed requests to router web interfaces

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic destined for router management interfaces
• Implement alerting for repeated failed authentication attempts or unusual activity on router administration ports
• Regularly review router logs for evidence of exploitation attempts or unexpected behavior

How to Mitigate CVE-2026-4534

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required
• Implement network segmentation to limit exposure of the router's management interface
• Monitor for any firmware updates from Tenda that address this vulnerability

Patch Information

At the time of publication, no vendor patch has been confirmed for this vulnerability. Organizations using affected Tenda FH451 devices should monitor the Tenda Official Website for security updates and firmware releases that address CVE-2026-4534.

Additional vulnerability details are available through VulDB CTI ID #352322.

Workarounds

• Configure firewall rules to block external access to the router's web management interface on port 80/443
• Use a VPN or jump host for administrative access to the router, avoiding direct exposure of the management interface
• Consider replacing affected devices with alternative router models if timely patches are not available
• Implement network-level access controls to restrict which hosts can communicate with the router's management interface

# Example: iptables rule to restrict router management access to specific subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP