CVE-2026-5684: Tenda CX12L Buffer Overflow Vulnerability

CVE-2026-5684 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda CX12L firmware version 16.03.53.12. This vulnerability affects the fromwebExcptypemanFilter function within the /goform/webExcptypemanFilter endpoint. By manipulating the page argument, an attacker with access to the local network can trigger a buffer overflow condition, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

This stack-based buffer overflow vulnerability in Tenda CX12L routers allows adjacent network attackers to potentially execute arbitrary code or crash the device, compromising network security and availability.

Affected Products

• Tenda CX12L firmware version 16.03.53.12
• Tenda CX12L router devices running vulnerable firmware

Discovery Timeline

• April 6, 2026 - CVE-2026-5684 published to NVD
• April 7, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5684

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected function fromwebExcptypemanFilter fails to properly validate the length of user-supplied input passed through the page argument before copying it to a fixed-size stack buffer.

When processing HTTP requests to the /goform/webExcptypemanFilter endpoint, the function does not implement adequate bounds checking, allowing an attacker to supply a maliciously crafted oversized value. This input overwrites adjacent memory on the stack, potentially corrupting the return address and enabling control flow hijacking.

The vulnerability requires the attacker to have access to the adjacent network (local network segment), which is typical for router-based attacks where an attacker has already gained a foothold within the target's local network infrastructure.

Root Cause

The root cause of this vulnerability is inadequate input validation in the fromwebExcptypemanFilter function. The code fails to verify that the page parameter length does not exceed the allocated buffer size before performing memory copy operations. This is a common programming error in embedded systems firmware where memory safety checks are often overlooked due to resource constraints or legacy codebases.

Attack Vector

The attack vector requires adjacent network access, meaning the attacker must be on the same local network segment as the vulnerable Tenda CX12L device. The attacker can send a specially crafted HTTP request to the /goform/webExcptypemanFilter endpoint with an oversized page parameter value. This triggers the stack-based buffer overflow, potentially allowing the attacker to overwrite the function's return address and redirect execution to attacker-controlled code.

The vulnerability has been publicly disclosed, and technical details are available through external references including the GitHub Issue Discussion and VulDB Vulnerability Detail. Network administrators should review these resources for additional technical context.

Detection Methods for CVE-2026-5684

Indicators of Compromise

• Unusual HTTP requests targeting /goform/webExcptypemanFilter with abnormally long page parameter values
• Router crashes or unexpected reboots following web interface access
• Anomalous network traffic patterns originating from or targeting the Tenda CX12L device
• Unexpected changes to router configuration or firmware

Detection Strategies

• Monitor and log all HTTP requests to the router's web management interface, particularly requests to /goform/webExcptypemanFilter
• Implement network intrusion detection rules to flag requests with oversized parameter values targeting Tenda devices
• Deploy network segmentation to isolate IoT and network infrastructure devices from general user traffic
• Use SentinelOne Singularity to monitor for suspicious network behavior and lateral movement attempts

Monitoring Recommendations

• Enable verbose logging on network firewall and intrusion detection systems for traffic destined to Tenda router management interfaces
• Regularly review router access logs for unusual patterns or unauthorized access attempts
• Implement alerting for any unexpected device behavior such as reboots or configuration changes
• Consider deploying network traffic analysis tools to identify potential exploitation attempts

How to Mitigate CVE-2026-5684

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Implement network segmentation to limit exposure of the vulnerable device
• Monitor for firmware updates from Tenda and apply patches as soon as they become available

Patch Information

At the time of publication, no official patch information has been released by Tenda. Network administrators should monitor the Tenda Official Website for security updates and firmware releases addressing this vulnerability. The vulnerability details have been submitted to VulDB which may provide updated remediation guidance.

Workarounds

• Implement strict access control lists (ACLs) to restrict access to the router's web management interface from only authorized IP addresses
• Disable the web management interface entirely if not required for day-to-day operations
• Place the vulnerable device behind a firewall with rules blocking unauthorized access to the management interface
• Consider replacing the affected device with an alternative that is not vulnerable until a patch is available

# Example: Restrict management interface access via firewall rules
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Log suspicious requests for forensic analysis
iptables -A INPUT -p tcp --dport 80 -m string --string "webExcptypemanFilter" --algo bm -j LOG --log-prefix "TENDA_CVE_2026_5684: "