CVE-2025-71021 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 serverName parameter of the sub_65A28 function, where improper input validation allows attackers to trigger a buffer overflow condition. This security flaw enables remote attackers to cause a Denial of Service (DoS) by sending specially crafted requests to the affected device.
Critical Impact
Remote attackers can crash the Tenda AX-1806 router without authentication, disrupting network connectivity for all connected devices and potentially leaving networks unprotected.
Affected Products
- Tenda AX-1806 Firmware version 1.0.0.1
- Tenda AX-1806 Hardware Device
Discovery Timeline
- 2026-01-14 - CVE-2025-71021 published to NVD
- 2026-01-20 - Last updated in NVD database
Technical Details for CVE-2025-71021
Vulnerability Analysis
This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when data written to a buffer exceeds its allocated size on the stack. In the context of the Tenda AX-1806 router, the sub_65A28 function fails to properly validate the length of the serverName parameter before copying it into a fixed-size stack buffer.
When an attacker sends a request with an oversized serverName value, the function writes beyond the buffer boundaries, corrupting adjacent stack memory. This corruption can overwrite critical data structures including return addresses and saved registers, causing the device to crash and become unresponsive.
The network-accessible nature of this vulnerability is particularly concerning for consumer routers, as these devices are typically exposed to the network and process incoming requests as part of their normal operation.
Root Cause
The root cause stems from insufficient bounds checking in the sub_65A28 function when processing the serverName parameter. The function copies user-supplied input into a stack-allocated buffer without verifying that the input length does not exceed the buffer capacity. This classic stack overflow pattern is a common vulnerability in embedded device firmware where memory safety mechanisms may be limited or absent.
Attack Vector
The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending a crafted HTTP request containing an oversized serverName parameter to the router's web management interface. The attack can be launched remotely from anywhere on the network that can reach the device.
The exploitation process involves sending a malformed request with a serverName value that exceeds the expected buffer size. When the vulnerable function processes this input, the stack overflow occurs, corrupting memory and causing the device to crash. Repeated exploitation could be used to persistently deny service to the network.
Detection Methods for CVE-2025-71021
Indicators of Compromise
- Unexpected router crashes or reboots without administrative action
- Network connectivity disruptions affecting all connected devices
- Abnormally large HTTP requests targeting the router's management interface
- Log entries showing malformed requests with unusually long serverName parameters
Detection Strategies
- Monitor network traffic for HTTP requests to the router containing abnormally long parameter values
- Implement intrusion detection rules to flag requests exceeding expected parameter lengths
- Configure network monitoring to alert on repeated router restarts or availability issues
- Deploy network segmentation to limit exposure of management interfaces
Monitoring Recommendations
- Enable logging on the router if available and forward logs to a central SIEM system
- Monitor uptime metrics for the Tenda AX-1806 device to detect unexpected restarts
- Implement network flow analysis to identify suspicious traffic patterns targeting the router
How to Mitigate CVE-2025-71021
Immediate Actions Required
- Restrict access to the router's web management interface to trusted networks only
- Place the router's management interface behind a firewall or VPN
- Monitor for firmware updates from Tenda that address this vulnerability
- Consider replacing affected devices with alternative hardware if no patch is available
Patch Information
At the time of publication, no vendor patch has been confirmed for this vulnerability. Users should monitor Tenda's official support channels for firmware updates addressing CVE-2025-71021. The GitHub Vulnerability Report provides additional technical details about this vulnerability.
Workarounds
- Disable remote management access to the router from WAN interfaces
- Implement network-level access controls to restrict who can reach the management interface
- Use a separate management VLAN to isolate administrative access to the device
- Consider deploying a firewall in front of the router to filter malicious requests
# Example: Restrict management access using iptables on an upstream device
# Block external access to router management port
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP
# Allow only trusted management subnet
iptables -I FORWARD -s 10.0.0.0/24 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
