CVE-2025-71019: Tenda AX1806 Firmware DoS Vulnerability

CVE-2025-71019 Overview

A stack overflow vulnerability has been identified in the Tenda AX-1806 router firmware version 1.0.0.1. The vulnerability exists in the wanSpeed parameter of the sub_65B5C function, which fails to properly validate input boundaries before processing. This flaw enables remote attackers to trigger a Denial of Service (DoS) condition by sending specially crafted HTTP requests to the affected device, potentially rendering the router unresponsive and disrupting network connectivity for all connected users.

Critical Impact

Remote attackers can exploit this stack overflow vulnerability without authentication to crash the Tenda AX-1806 router, causing network-wide service disruption for home and small business environments.

Affected Products

• Tenda AX-1806 Firmware version 1.0.0.1
• Tenda AX-1806 Hardware Device

Discovery Timeline

• 2026-01-15 - CVE-2025-71019 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-71019

Vulnerability Analysis

This vulnerability is classified as CWE-121: Stack-based Buffer Overflow, a memory corruption flaw where user-supplied input exceeds the allocated stack buffer size. The sub_65B5C function in the Tenda AX-1806 firmware processes the wanSpeed parameter without implementing adequate bounds checking on the input data length.

When an attacker submits a request containing an oversized wanSpeed parameter value, the data overflows the designated stack buffer, corrupting adjacent memory regions including the saved return address. While the primary impact documented is Denial of Service through application crash, stack-based buffer overflows in embedded systems firmware can potentially lead to more severe consequences if the execution flow can be redirected.

The vulnerability is remotely exploitable over the network with no authentication required and no user interaction necessary, making it particularly dangerous for internet-exposed devices.

Root Cause

The root cause of CVE-2025-71019 lies in insufficient input validation within the sub_65B5C function. The firmware fails to verify the length of the wanSpeed parameter against the stack buffer's allocated size before copying the data. This classic programming error in memory-unsafe languages (commonly C/C++ in embedded firmware) allows attackers to write beyond buffer boundaries, corrupting the call stack and causing program execution to terminate abnormally.

Attack Vector

The attack vector is network-based, requiring the attacker to craft a malicious HTTP request targeting the router's web management interface. The attacker sends a request with an excessively long wanSpeed parameter value to the vulnerable function endpoint. The request does not require prior authentication, making any network-accessible Tenda AX-1806 router running vulnerable firmware a potential target.

The exploitation process involves sending a crafted request with a wanSpeed parameter containing data exceeding the expected buffer size. When the sub_65B5C function processes this input, the stack buffer overflow occurs, corrupting memory and crashing the device. For detailed technical information about this vulnerability, see the GitHub Vulnerability Report.

Detection Methods for CVE-2025-71019

Indicators of Compromise

• Unexpected router reboots or complete unresponsiveness requiring manual power cycling
• HTTP request logs (if available) showing abnormally large wanSpeed parameter values
• Network monitoring alerts indicating malformed or oversized requests to the router's management interface
• Repeated connection drops affecting all devices on the network segment

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with excessively long wanSpeed parameters targeting Tenda devices
• Monitor for repeated crash patterns or unexpected device restarts in router management logs
• Deploy web application firewall (WAF) rules to block requests exceeding normal parameter length thresholds
• Use network flow analysis to detect anomalous traffic patterns directed at router management ports

Monitoring Recommendations

• Enable logging on upstream network devices to capture traffic destined for the router's management interface
• Implement availability monitoring to detect sudden device outages indicative of DoS attacks
• Configure alerting for multiple failed connection attempts or service interruptions on the affected network segment
• Review network traffic logs for requests containing suspiciously large payloads targeting router endpoints

How to Mitigate CVE-2025-71019

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
• Place the router behind a network firewall that can filter malicious requests
• Monitor for firmware updates from Tenda and apply security patches when available

Patch Information

No vendor patch information is currently available for CVE-2025-71019. Users should monitor Tenda's official support channels for firmware updates addressing this vulnerability. Given the lack of an official fix, implementing network-level mitigations is strongly recommended.

Workarounds

• Disable WAN-side access to the router's administrative interface to prevent external exploitation
• Implement access control lists (ACLs) on the router to restrict management access to specific trusted internal IP addresses
• Deploy network segmentation to limit the impact of a successful DoS attack on the router
• Consider replacing the affected device with an alternative router model if security updates are not forthcoming from the vendor

# Example: Restrict management interface access using upstream firewall
# Block external access to common 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 only trusted internal management IPs
iptables -I FORWARD -s <trusted_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT