CVE-2025-70656: Tenda AX1806 Firmware DoS Vulnerability

CVE-2025-70656 Overview

A stack overflow vulnerability has been discovered in the Tenda AX-1806 wireless router firmware version 1.0.0.1. The vulnerability exists within the sub_65B5C function, specifically in the handling of the mac parameter. Attackers can exploit this flaw by sending a specially crafted request to the device, causing a stack-based buffer overflow that leads to a Denial of Service (DoS) condition.

Critical Impact

This vulnerability allows remote attackers to crash affected Tenda AX-1806 routers without authentication, potentially disrupting network connectivity for all connected devices.

Affected Products

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

Discovery Timeline

• 2026-01-15 - CVE-2025-70656 published to NVD
• 2026-01-20 - Last updated in NVD database

Technical Details for CVE-2025-70656

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption vulnerability that occurs when a program writes data beyond the boundaries of a fixed-size stack buffer. In this case, the sub_65B5C function within the Tenda AX-1806 firmware fails to properly validate the length of the mac parameter before copying it to a stack buffer.

When an attacker supplies an oversized mac parameter value, the function copies this data without bounds checking, causing the stack buffer to overflow. This overwrites adjacent memory on the stack, including critical data such as return addresses and saved registers, ultimately causing the device to crash and become unresponsive.

The vulnerability is remotely exploitable over the network and requires no authentication or user interaction, making it particularly dangerous for devices exposed to untrusted networks.

Root Cause

The root cause of this vulnerability is improper input validation in the sub_65B5C function. The firmware does not adequately verify the length of the mac parameter before processing it, allowing an attacker to submit a value that exceeds the allocated buffer size. This lack of boundary checking is a common vulnerability pattern in embedded device firmware where memory-constrained environments may lead developers to omit proper input sanitization.

Attack Vector

The attack vector is network-based, allowing remote exploitation without authentication. An attacker can craft a malicious HTTP request containing an oversized mac parameter value targeting the vulnerable function. When the device processes this request, the stack overflow occurs, causing the device to crash. This attack can be repeated to maintain a persistent denial of service condition against the affected router.

The vulnerability mechanism involves sending a crafted request to the device's web management interface with a mac parameter containing data that exceeds the expected buffer size. When the sub_65B5C function processes this input, it copies the oversized data to a fixed-size stack buffer without proper bounds checking, resulting in memory corruption and device crash. For detailed technical analysis, refer to the GitHub Vulnerability Report.

Detection Methods for CVE-2025-70656

Indicators of Compromise

• Unexpected router reboots or unresponsive web management interface
• Network connectivity loss for devices connected to the Tenda AX-1806 router
• Abnormal HTTP requests containing unusually large mac parameter values in router logs
• Repeated crash dumps or error logs from the router if diagnostic logging is enabled

Detection Strategies

• Monitor network traffic for HTTP requests with abnormally large mac parameters targeting the router
• Implement intrusion detection rules to flag requests with oversized parameters to embedded device management interfaces
• Configure network monitoring to alert on router availability issues or unexpected reboots
• Deploy network segmentation to isolate IoT/router management interfaces from untrusted networks

Monitoring Recommendations

• Enable logging on the Tenda AX-1806 if supported and monitor for crash events
• Implement uptime monitoring for critical network infrastructure devices
• Use network flow analysis to detect unusual traffic patterns targeting router management ports
• Consider deploying a network-based IDS/IPS in front of vulnerable devices

How to Mitigate CVE-2025-70656

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Place the Tenda AX-1806 behind a firewall that filters external access to management interfaces
• Disable remote management if not required for operations
• Monitor for firmware updates from Tenda that address this vulnerability

Patch Information

As of the last NVD update on 2026-01-20, no official patch information has been published by Tenda. Organizations should monitor Tenda's official support channels for firmware updates that address CVE-2025-70656. Until a patch is available, implementing the workarounds below is strongly recommended.

Workarounds

• Configure firewall rules to block external access to the router's management interface (typically port 80/443)
• Enable access control lists (ACLs) on the router to restrict management access to specific trusted IP addresses
• Consider placing vulnerable devices on an isolated network segment
• If the device supports it, disable the web management interface entirely and use alternative management methods

# Example iptables rules to restrict access to router management interface
# Apply on upstream firewall or gateway device
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 workstation
iptables -I FORWARD -s <admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <admin_ip> -d <router_ip> -p tcp --dport 443 -j ACCEPT