CVE-2026-3677: Tenda FH451 Buffer Overflow Vulnerability

CVE-2026-3677 Overview

A stack-based buffer overflow vulnerability has been discovered in the Tenda FH451 wireless router firmware version 1.0.0.9. This vulnerability affects the fromSetCfm function located in the /goform/setcfm file. Remote attackers can exploit this flaw by manipulating the funcname and funcpara1 arguments, potentially leading to arbitrary code execution or denial of service conditions on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to execute arbitrary code or crash affected Tenda FH451 routers, compromising network security and device availability.

Affected Products

• Tenda FH451 Firmware version 1.0.0.9
• Tenda FH451 Hardware
• Tenda FH451 Wireless Router devices running vulnerable firmware

Discovery Timeline

• 2026-03-07 - CVE-2026-3677 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3677

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromSetCfm function in the Tenda FH451 firmware fails to properly validate input length when processing the funcname and funcpara1 parameters. This allows an attacker to submit oversized input that exceeds the allocated stack buffer, overwriting adjacent memory regions including the return address.

The vulnerability is network-accessible, meaning attackers can exploit it remotely without requiring physical access to the device. The attack requires low privileges and no user interaction, making it particularly dangerous for devices exposed to untrusted networks.

Root Cause

The root cause stems from insufficient bounds checking in the fromSetCfm function when handling user-supplied input through the web interface. The function copies data from the funcname and funcpara1 HTTP parameters directly into fixed-size stack buffers without verifying that the input length does not exceed the buffer capacity. This classic buffer overflow pattern allows attackers to overwrite stack memory, potentially including saved return addresses and other critical data structures.

Attack Vector

The attack is performed remotely over the network by sending crafted HTTP requests to the /goform/setcfm endpoint. An authenticated attacker can manipulate the funcname or funcpara1 parameters with oversized payloads to trigger the buffer overflow condition.

The exploitation workflow involves:

1. The attacker identifies a vulnerable Tenda FH451 device on the network running firmware version 1.0.0.9
2. A malicious HTTP POST request is crafted targeting the /goform/setcfm endpoint
3. The funcname or funcpara1 parameters are populated with data exceeding the expected buffer size
4. The fromSetCfm function processes the request without proper length validation
5. Stack memory is corrupted, potentially allowing control flow hijacking or causing a device crash

For technical details regarding this vulnerability, refer to the GitHub Vulnerability Database Entry.

Detection Methods for CVE-2026-3677

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/setcfm with abnormally large parameter values
• Router crashes or spontaneous reboots without administrative action
• Unusual network traffic patterns originating from or targeting the router's management interface
• Modified router configurations or settings that were not authorized

Detection Strategies

• Monitor HTTP traffic to Tenda FH451 devices for requests containing oversized funcname or funcpara1 parameters
• Implement web application firewall (WAF) rules to detect and block requests with abnormally large parameter values to /goform/setcfm
• Deploy network intrusion detection systems (NIDS) with signatures targeting stack-based buffer overflow exploitation attempts
• Review device logs for repeated authentication failures or unusual access patterns to the web management interface

Monitoring Recommendations

• Enable logging on all Tenda FH451 devices and forward logs to a centralized SIEM for analysis
• Implement network segmentation to isolate IoT and router management interfaces from untrusted networks
• Set up alerts for unexpected device reboots or configuration changes
• Regularly audit network traffic for anomalous patterns targeting router management endpoints

How to Mitigate CVE-2026-3677

Immediate Actions Required

• Restrict access to the Tenda FH451 web management interface to trusted IP addresses only
• Place affected devices behind a firewall that filters incoming requests to the /goform/setcfm endpoint
• Disable remote management capabilities if not required for operations
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no vendor patch has been confirmed for this vulnerability. Administrators should monitor Tenda's official channels for security updates. The vulnerability is documented in the VulDB Entry #349579 which may contain additional remediation guidance as it becomes available.

Workarounds

• Implement network access control lists (ACLs) to restrict management interface access to authorized administrators only
• Configure firewall rules to block external access to the router's web interface on port 80/443
• Consider deploying a reverse proxy with input validation to filter malicious requests before they reach the device
• If feasible, consider replacing affected devices with alternative hardware that receives regular security updates

# Example firewall rule to restrict access to router management interface
# Block external access to /goform/ endpoints on Tenda FH451
iptables -A INPUT -p tcp --dport 80 -m string --string "/goform/" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/goform/" --algo bm -j DROP

# Allow management access only from trusted 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