CVE-2026-3678: Tenda FH451 Buffer Overflow Vulnerability

CVE-2026-3678 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda FH451 wireless router firmware version 1.0.0.9. The vulnerability exists in the sub_3C434 function within the /goform/AdvSetWan endpoint. An attacker can exploit this flaw by manipulating the wanmode or PPPOEPassword parameters, causing a stack-based buffer overflow condition that could lead to remote code execution or denial of service.

Critical Impact

This vulnerability allows remote attackers to trigger a stack-based buffer overflow on Tenda FH451 routers, potentially enabling complete device compromise. The exploit has been publicly disclosed and may be actively utilized by threat actors targeting vulnerable network infrastructure.

Affected Products

• Tenda FH451 Firmware version 1.0.0.9
• Tenda FH451 Hardware Device
• Tenda FH451 Firmware (all builds of 1.0.0.9)

Discovery Timeline

• 2026-03-07 - CVE-2026-3678 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3678

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), representing a fundamental memory safety issue in the Tenda FH451 router firmware. The vulnerable function sub_3C434 processes user-supplied input from the /goform/AdvSetWan web interface endpoint without adequate boundary checks.

The attack can be initiated remotely over the network, requiring low-privileged access to the router's web management interface. No user interaction is required beyond the initial authentication, making this vulnerability particularly dangerous in environments where the router's management interface is exposed.

The exploitation of this vulnerability could result in complete compromise of the affected device, including the ability to execute arbitrary code with elevated privileges, intercept network traffic, or render the device inoperable.

Root Cause

The root cause of CVE-2026-3678 lies in insufficient input validation within the sub_3C434 function. When processing the wanmode or PPPOEPassword arguments from HTTP POST requests to the /goform/AdvSetWan endpoint, the function copies user-supplied data to a fixed-size stack buffer without properly verifying the input length. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including saved return addresses and other critical control data.

The firmware developers failed to implement proper bounds checking or use secure string handling functions, leaving the device vulnerable to exploitation through crafted HTTP requests containing oversized parameter values.

Attack Vector

The attack vector is network-based, targeting the router's web management interface. An attacker with low-privileged access to the administrative interface can send specially crafted HTTP POST requests to the /goform/AdvSetWan endpoint. By providing maliciously long values for the wanmode or PPPOEPassword parameters, the attacker triggers the stack-based buffer overflow in the sub_3C434 function.

The vulnerability exploitation flow involves submitting oversized input data through the WAN configuration form, which causes the vulnerable function to overflow its stack buffer. This overflow can corrupt adjacent memory regions, potentially allowing the attacker to hijack program execution flow and gain control of the device.

A proof-of-concept for this vulnerability has been publicly disclosed. Technical details and exploitation methodology can be found in the GitHub Vulnerability PoC repository. Additional vulnerability information is available through VulDB #349580.

Detection Methods for CVE-2026-3678

Indicators of Compromise

• Unusual HTTP POST requests to /goform/AdvSetWan with abnormally large parameter values
• Router crashes or unexpected reboots following administrative interface access
• Suspicious network traffic patterns originating from or directed at the router's management interface
• Unexpected changes to router WAN configuration settings

Detection Strategies

• Monitor HTTP traffic to the router's web interface for POST requests to /goform/AdvSetWan containing oversized wanmode or PPPOEPassword parameters
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Deploy web application firewall rules to block requests with excessively long parameter values to router administration endpoints
• Review router access logs for repeated failed authentication attempts or suspicious administrative activity

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices to capture traffic destined for router management interfaces
• Implement alerting for any crashes or service interruptions on Tenda FH451 devices
• Monitor for firmware integrity changes or unauthorized configuration modifications
• Establish baseline network behavior patterns to detect anomalous activity originating from router devices

How to Mitigate CVE-2026-3678

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only using firewall rules
• Disable remote management access from WAN interfaces if not required
• Place the router's administrative interface behind a VPN or isolated management network
• Monitor the Tenda Official Website for security updates and firmware patches

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Organizations should monitor vendor channels for security updates and apply patches immediately upon availability. The affected firmware version is 1.0.0.9 and users should upgrade to the latest firmware version when Tenda releases a security fix.

Workarounds

• Implement network segmentation to isolate vulnerable Tenda FH451 devices from untrusted network segments
• Configure access control lists (ACLs) to restrict administrative interface access to specific trusted IP addresses
• Consider deploying a reverse proxy with input validation capabilities in front of the router management interface
• Evaluate replacing vulnerable devices with alternative hardware if patches are not released in a timely manner

# Example: Restrict router admin interface access using iptables on upstream firewall
# Block external access to router management on port 80
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
# Allow only management VLAN access
iptables -I FORWARD -s 10.0.10.0/24 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT