CVE-2025-71026: Tenda AX-3 Router DoS Vulnerability

CVE-2025-71026 Overview

A stack overflow vulnerability has been discovered in the Tenda AX-3 router firmware version 16.03.12.10_CN. The vulnerability exists within the wanSpeed2 parameter of the fromAdvSetMacMtuWan function. Attackers can exploit this flaw by sending specially crafted requests to the affected device, resulting in a Denial of Service (DoS) condition.

Critical Impact

This stack overflow vulnerability in the Tenda AX-3 router allows remote attackers to cause a Denial of Service condition, potentially disrupting network connectivity for all connected devices.

Affected Products

• Tenda AX-3 firmware version 16.03.12.10_CN

Discovery Timeline

• 2026-01-13 - CVE-2025-71026 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-71026

Vulnerability Analysis

This vulnerability is classified as a stack overflow, a type of memory corruption vulnerability that occurs when a program writes data beyond the boundaries of a stack buffer. In the context of the Tenda AX-3 router, the fromAdvSetMacMtuWan function fails to properly validate the length of input provided through the wanSpeed2 parameter.

When an attacker sends an excessively long or malformed value in the wanSpeed2 parameter, the function copies this data onto the stack without adequate bounds checking. This overflow corrupts adjacent memory on the stack, which can overwrite critical data structures including return addresses and saved registers. The result is a crash of the affected service or the entire device, causing a Denial of Service condition.

Root Cause

The root cause of this vulnerability is improper input validation in the fromAdvSetMacMtuWan function. The function does not enforce proper boundary checks when processing the wanSpeed2 parameter, allowing user-supplied input to overflow the allocated stack buffer. This is a common firmware security issue where functions that handle user input fail to validate the size of incoming data before copying it to fixed-size buffers.

Attack Vector

The vulnerability can be exploited remotely by sending a crafted HTTP request to the router's web management interface. An attacker with network access to the device can construct a malicious request containing an oversized wanSpeed2 parameter value. When the router processes this request through the fromAdvSetMacMtuWan function, the stack overflow occurs.

The attack does not require authentication in scenarios where the web interface is accessible. The exploitation is straightforward as it only requires sending a single malformed request to trigger the crash. For technical details, see the GitHub Vulnerability Report.

Detection Methods for CVE-2025-71026

Indicators of Compromise

• Unexpected router reboots or service interruptions
• Abnormal HTTP requests to the router management interface containing oversized parameter values
• Crash logs indicating memory corruption or segmentation faults in web server processes
• Network connectivity disruptions affecting all devices connected to the router

Detection Strategies

• Monitor inbound HTTP traffic to the router management interface for requests with abnormally large parameter values
• Configure network intrusion detection systems (IDS) to alert on malformed requests targeting the fromAdvSetMacMtuWan endpoint
• Implement log analysis to detect patterns of repeated router crashes or restarts
• Deploy network traffic analysis tools to identify suspicious activity targeting IoT devices

Monitoring Recommendations

• Enable verbose logging on the router if available to capture request details
• Set up availability monitoring to detect unexpected device downtime
• Monitor router CPU and memory utilization for anomalous patterns before crashes
• Implement network segmentation to isolate IoT devices and monitor traffic between segments

How to Mitigate CVE-2025-71026

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management if not required
• Ensure the router is behind a firewall that blocks unauthorized access to management ports
• Monitor for firmware updates from Tenda that address this vulnerability

Patch Information

At the time of publication, no official patch information is available from the vendor. Users should monitor Tenda's official website and support channels for security updates addressing this vulnerability. The vulnerability was documented in a GitHub vulnerability report.

Workarounds

• Disable the web management interface when not in use
• Implement access control lists (ACLs) to limit which IP addresses can access the management interface
• Place the router behind a network firewall with rules blocking external access to management ports
• Consider using a VPN for remote management access instead of exposing the interface directly

# Example: Restrict management interface access via upstream firewall
# Block external access to router management port (example for iptables)
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