CVE-2026-3679: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-3679 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda FH451 router firmware version 1.0.0.9. The vulnerability exists within the formQuickIndex function located in the /goform/QuickIndex endpoint. Attackers can exploit this flaw by manipulating the mit_linktype or PPPOEPassword arguments, leading to a stack-based buffer overflow condition. This vulnerability can be exploited remotely, and public exploit information is available.

Critical Impact

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

Affected Products

• Tenda FH451 Firmware version 1.0.0.9
• Tenda FH451 Hardware Device
• Tenda F451 Firmware

Discovery Timeline

• 2026-03-07 - CVE-2026-3679 published to NVD
• 2026-03-09 - Last updated in NVD database

Technical Details for CVE-2026-3679

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formQuickIndex function in the Tenda FH451 router firmware fails to properly validate the length of user-supplied input for the mit_linktype and PPPOEPassword parameters before copying them to a stack buffer.

When an attacker submits an overly long string through either of these parameters via the /goform/QuickIndex endpoint, the function copies the data beyond the allocated buffer boundaries on the stack. This overflow can overwrite adjacent memory, including the return address, potentially allowing an attacker to redirect program execution to malicious code.

The network-accessible nature of this vulnerability combined with the low attack complexity makes it a significant risk for exposed devices. Successful exploitation could result in complete compromise of the router's confidentiality, integrity, and availability.

Root Cause

The root cause stems from insufficient bounds checking in the formQuickIndex function when processing HTTP POST requests to /goform/QuickIndex. The function uses unsafe string handling operations that do not validate input length against the fixed-size stack buffer, allowing attackers to supply oversized input that overflows the buffer boundary. This is a common vulnerability pattern in embedded router firmware where memory-constrained environments often lead to unsafe C programming practices.

Attack Vector

The attack can be initiated remotely over the network by sending a crafted HTTP request to the vulnerable endpoint. An attacker with low-level privileges can target the /goform/QuickIndex endpoint and supply malicious input in the mit_linktype or PPPOEPassword parameters. The attack does not require user interaction, making it suitable for automated exploitation.

The vulnerability mechanism involves sending an HTTP POST request to the router's web management interface with an oversized value in the vulnerable parameters. When the formQuickIndex function processes this request, the lack of proper input validation causes a stack buffer overflow. For detailed technical analysis, refer to the GitHub Vulnerability Repository.

Detection Methods for CVE-2026-3679

Indicators of Compromise

• Abnormal HTTP POST requests to /goform/QuickIndex with unusually long mit_linktype or PPPOEPassword parameters
• Unexpected router reboots or crashes that may indicate exploitation attempts
• Unauthorized configuration changes on the router's web management interface
• Network traffic anomalies originating from or destined to the router management ports

Detection Strategies

• Monitor HTTP traffic to the router management interface for POST requests to /goform/QuickIndex containing oversized parameter values
• Implement intrusion detection signatures to flag requests with mit_linktype or PPPOEPassword parameters exceeding normal length thresholds
• Deploy network-based anomaly detection to identify unusual traffic patterns targeting router management endpoints
• Review router access logs for repeated failed authentication or suspicious management interface access patterns

Monitoring Recommendations

• Restrict access to the router's web management interface to trusted internal networks only
• Enable logging on the router and forward logs to a centralized SIEM for analysis
• Set up alerts for any external network access attempts to the router management ports (typically 80, 443, or 8080)
• Regularly audit network traffic for signs of reconnaissance or exploitation targeting embedded devices

How to Mitigate CVE-2026-3679

Immediate Actions Required

• Disable remote management access to the Tenda FH451 router if not required for operations
• Implement network segmentation to isolate the router's management interface from untrusted networks
• Place the router behind a firewall or access control list that restricts management interface access to authorized IP addresses only
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor VulDB #349581 and the vendor's official channels for security updates. The affected firmware version is 1.0.0.9 for the Tenda FH451/F451 router series.

Workarounds

• Disable the web management interface entirely if remote administration is not required
• Configure firewall rules to block external access to the router's management ports
• Use a VPN for any necessary remote management access rather than exposing the management interface directly
• Consider replacing the vulnerable device with an alternative router solution if no patch becomes available

# Example firewall rule to restrict management interface access
# Block external access to router management port (adjust IP and port as needed)
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

# Allow management access only from specific trusted host
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP