CVE-2025-71027: Tenda AX-3 Router DoS Vulnerability

CVE-2025-71027 Overview

A stack overflow vulnerability was discovered in the Tenda AX-3 router firmware version 16.03.12.10_CN. The vulnerability exists in the wanMTU2 parameter of the fromAdvSetMacMtuWan function, which fails to properly validate input boundaries before processing user-supplied data. This flaw allows remote attackers to cause a Denial of Service (DoS) condition by sending specially crafted requests to the affected device.

Critical Impact

Attackers can exploit this stack overflow vulnerability to crash the Tenda AX-3 router, causing network disruption and service unavailability for all connected devices.

Affected Products

• Tenda AX-3 v16.03.12.10_CN

Discovery Timeline

• 2026-01-13 - CVE CVE-2025-71027 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-71027

Vulnerability Analysis

This vulnerability is a classic stack overflow condition occurring within the fromAdvSetMacMtuWan function of the Tenda AX-3 router firmware. The function processes the wanMTU2 parameter without adequate bounds checking, allowing an attacker to supply an oversized input value that exceeds the allocated stack buffer. When the function attempts to copy this malformed input into a fixed-size stack buffer, it overwrites adjacent memory on the stack, leading to memory corruption.

The exploitation of this vulnerability results in a Denial of Service condition where the affected router becomes unresponsive or crashes entirely. Given the nature of router firmware vulnerabilities, successful exploitation could disrupt network connectivity for all devices relying on the affected router.

Root Cause

The root cause of this vulnerability is improper input validation in the fromAdvSetMacMtuWan function. The wanMTU2 parameter is processed without verifying that its length falls within acceptable bounds before being copied to a stack-allocated buffer. This absence of boundary checking allows attackers to supply input that exceeds the buffer's capacity, resulting in stack memory corruption.

Attack Vector

The attack is executed by sending a maliciously crafted HTTP request to the router's web management interface. The request targets the fromAdvSetMacMtuWan function with an oversized wanMTU2 parameter value. When the router processes this request, the stack overflow occurs, corrupting critical stack data structures and causing the device to crash or become unresponsive.

The vulnerability can be triggered remotely by any attacker with network access to the router's administration interface. If the web management interface is exposed to the internet or accessible from untrusted network segments, the attack surface increases significantly.

Detailed technical documentation is available in the GitHub Vulnerability Documentation.

Detection Methods for CVE-2025-71027

Indicators of Compromise

• Unexpected router reboots or crashes without apparent cause
• HTTP requests to the router's web interface containing abnormally large wanMTU2 parameter values
• Network connectivity disruptions affecting all devices connected to the router
• Log entries indicating memory access violations or segmentation faults in router system logs

Detection Strategies

• Monitor HTTP traffic to the router's management interface for requests containing unusually large parameter values in the wanMTU2 field
• Implement network intrusion detection rules to identify requests targeting the fromAdvSetMacMtuWan endpoint with anomalous payload sizes
• Configure alerts for unexpected router reboots or service restarts that may indicate exploitation attempts
• Audit access logs for repeated requests to advanced WAN configuration endpoints from suspicious sources

Monitoring Recommendations

• Deploy network-based anomaly detection to identify unusual traffic patterns directed at the router's management interface
• Implement logging for all administrative access attempts to the Tenda AX-3 device
• Monitor router uptime and availability metrics to detect potential DoS exploitation
• Review firewall logs for connection attempts to the router's web management port from unauthorized sources

How to Mitigate CVE-2025-71027

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Disable remote management features if not required for operational purposes
• Implement firewall rules to block external access to the router's administration ports
• Monitor for firmware updates from Tenda that address this vulnerability
• Consider network segmentation to isolate the router's management interface from untrusted network segments

Patch Information

As of the last modification date (2026-01-13), no official patch information has been published by the vendor. Users should monitor Tenda's official security advisories and firmware download pages for updates addressing this vulnerability. Additional technical details can be found in the GitHub Vulnerability Documentation.

Workarounds

• Disable the web-based administration interface and use alternative management methods if available
• Implement access control lists (ACLs) to restrict which IP addresses can access the router's management interface
• Place the router behind an additional firewall that filters incoming traffic to management ports
• If remote management is required, use a VPN to secure access rather than exposing the interface directly

# Example: Restrict access to router management interface via firewall
# Block external access to common router management ports
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 only specific trusted IP addresses for management access
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT