CVE-2025-71020: Tenda AX-1806 Stack Overflow DoS Vulnerability

CVE-2025-71020 Overview

A stack overflow vulnerability has been discovered in the Tenda AX-1806 router firmware version 1.0.0.1. The vulnerability exists within the security parameter handling in the sub_4C408 function. When exploited, this flaw allows remote attackers to cause a Denial of Service (DoS) condition on affected devices by sending specially crafted requests to the vulnerable endpoint.

Critical Impact

Remote attackers can crash affected Tenda AX-1806 routers without authentication, disrupting network connectivity for all connected devices.

Affected Products

• Tenda AX-1806 v1.0.0.1

Discovery Timeline

• 2026-01-16 - CVE-2025-71020 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-71020

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow). The flaw resides in the sub_4C408 function within the Tenda AX-1806 firmware, which improperly handles the security parameter. When processing input data, the function fails to adequately validate the size of user-supplied input before copying it to a fixed-size stack buffer.

The network-accessible nature of this vulnerability means attackers can target devices remotely without requiring any prior authentication or user interaction. The exploitation results in memory corruption on the stack, leading to a crash condition that renders the router unresponsive and requires a manual reboot to restore functionality.

Root Cause

The root cause is insufficient bounds checking in the sub_4C408 function when processing the security parameter. The function allocates a fixed-size buffer on the stack but does not properly validate that incoming data fits within this allocated space. When an attacker supplies an oversized or malformed value for the security parameter, the data overflows the stack buffer boundaries, corrupting adjacent stack memory and causing the application to crash.

Attack Vector

The attack is network-based and can be executed remotely by sending a crafted HTTP request to the router's web management interface. An attacker can construct a request with an oversized security parameter value that exceeds the expected buffer size in the sub_4C408 function. Upon processing this malicious input, the stack overflow condition is triggered, causing the router firmware to crash. No authentication is required to exploit this vulnerability, making it particularly dangerous for internet-exposed devices.

For technical details on the vulnerability mechanism, refer to the GitHub Vulnerability Report.

Detection Methods for CVE-2025-71020

Indicators of Compromise

• Unexpected router reboots or unresponsive web management interface
• Abnormal HTTP requests with unusually large security parameter values targeting the router
• Network connectivity interruptions coinciding with external access attempts to the router
• Log entries showing crashes or memory errors in router diagnostics (if available)

Detection Strategies

• Monitor network traffic for HTTP requests with abnormally large parameter values directed at router management interfaces
• Implement intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Deploy network segmentation to isolate router management interfaces from untrusted networks
• Review access logs for repeated connection attempts to router administration endpoints from unknown sources

Monitoring Recommendations

• Enable logging on the Tenda AX-1806 if supported and forward logs to a centralized SIEM solution
• Configure network monitoring to alert on unusual traffic patterns to port 80/443 on the router
• Implement uptime monitoring for the router to detect unexpected restarts indicative of DoS attacks
• Monitor for reconnaissance activity targeting known Tenda router vulnerabilities

How to Mitigate CVE-2025-71020

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required for operations
• Place the router behind a firewall that can filter malicious traffic patterns
• Monitor Tenda's official channels for firmware updates addressing this vulnerability

Patch Information

At the time of this publication, no official patch has been released by Tenda for this vulnerability. Administrators should monitor Tenda's official website and support channels for firmware updates. The vulnerability was documented in a GitHub Vulnerability Report which provides additional technical details.

Workarounds

• Configure firewall rules to block external access to the router's management interface
• Implement network access control lists (ACLs) to restrict administrative access to specific IP addresses
• Consider deploying an additional security appliance or firewall in front of the vulnerable router
• If the device must be internet-accessible, use a VPN to secure access to the management interface

# Example: Restrict router management access via upstream firewall
# Block external access to router management ports
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP
# Allow management only from trusted admin subnet
iptables -I FORWARD -s <trusted_subnet> -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <trusted_subnet> -d <router_ip> -p tcp --dport 443 -j ACCEPT