CVE-2025-9605: Tenda AC21 Buffer Overflow Vulnerability

CVE-2025-9605 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC21 and AC23 wireless routers running firmware version 16.03.08.16. The vulnerability exists in the GetParentControlInfo function located in the /goform/GetParentControlInfo file. Improper handling of the mac argument allows attackers to trigger a stack-based buffer overflow condition. This vulnerability can be exploited remotely without authentication, potentially enabling attackers to execute arbitrary code or cause a denial of service on affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially gain complete control over affected Tenda routers, compromising network security and enabling further attacks on connected devices.

Affected Products

• Tenda AC21 Firmware version 16.03.08.16
• Tenda AC21 Hardware
• Tenda AC23 Firmware version 16.03.08.16
• Tenda AC23 Hardware

Discovery Timeline

• 2025-08-29 - CVE-2025-9605 published to NVD
• 2025-09-03 - Last updated in NVD database

Technical Details for CVE-2025-9605

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The GetParentControlInfo function in the Tenda router firmware fails to properly validate the length of the mac parameter before copying it into a fixed-size stack buffer. When an oversized value is supplied for this argument, it overflows the buffer boundary and overwrites adjacent memory on the stack.

The vulnerability is exploitable remotely over the network without requiring any authentication or user interaction. An attacker can craft a malicious HTTP request to the /goform/GetParentControlInfo endpoint with an oversized mac parameter to trigger the overflow condition. Successful exploitation could allow the attacker to overwrite the return address on the stack, redirect program execution, and potentially achieve arbitrary code execution with the privileges of the router's web service.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the GetParentControlInfo function. The firmware does not properly validate the length of user-supplied input for the mac argument before processing it, allowing data to be written beyond the allocated buffer boundaries on the stack. This is a classic stack-based buffer overflow vulnerability pattern commonly found in embedded device firmware.

Attack Vector

The attack can be launched remotely over the network by sending a specially crafted HTTP request to the vulnerable /goform/GetParentControlInfo endpoint. The attacker provides an oversized value for the mac parameter, which causes the function to write data beyond the allocated buffer on the stack.

The vulnerability has been publicly disclosed with proof-of-concept details available in security research repositories. Exploitation does not require authentication or user interaction, making it particularly dangerous for internet-exposed devices. For detailed technical analysis, refer to the GitHub PoC Repository for AC21 and the GitHub PoC for AC23 Buffer Overflow.

Detection Methods for CVE-2025-9605

Indicators of Compromise

• Unusual HTTP POST requests to /goform/GetParentControlInfo with abnormally large mac parameter values
• Unexpected router crashes, reboots, or service interruptions
• Anomalous outbound network traffic from the router indicating potential compromise
• Changes to router configuration or DNS settings without administrator action

Detection Strategies

• Monitor HTTP traffic to Tenda routers for requests targeting /goform/GetParentControlInfo with oversized parameters
• Implement network intrusion detection rules to identify buffer overflow attack patterns against embedded devices
• Deploy endpoint detection solutions capable of monitoring IoT device behavior for anomalies
• Review router logs for repeated crash events or unexpected restarts that may indicate exploitation attempts

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic to and from Tenda routers
• Implement network segmentation to isolate IoT devices and limit lateral movement potential
• Configure alerts for unusual traffic patterns or access attempts to router administration interfaces
• Regularly audit firmware versions across deployed Tenda devices to identify vulnerable units

How to Mitigate CVE-2025-9605

Immediate Actions Required

• Identify all Tenda AC21 and AC23 devices running firmware version 16.03.08.16 in your environment
• Restrict network access to the router's web administration interface to trusted IP addresses only
• Disable remote administration features if not required for operations
• Place affected devices behind additional network security controls such as firewalls or IPS systems
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

As of the last update on 2025-09-03, no official patch has been released by Tenda to address this vulnerability. Organizations should monitor Tenda's official channels for security updates and apply patches immediately upon availability. Additional technical details can be found in the VulDB Advisory #321783.

Workarounds

• Implement strict access control lists (ACLs) to restrict access to the router management interface
• Use firewall rules to block external access to the /goform/ endpoint on affected devices
• Consider replacing affected devices with alternative hardware if patches are not forthcoming
• Implement network-level intrusion prevention to detect and block exploitation attempts

# Example: Firewall rule to restrict access to router management interface
# Block external access to Tenda router web interface on port 80
iptables -A INPUT -p tcp --dport 80 -d <router_ip> -s ! <trusted_network> -j DROP

# Restrict access to goform endpoints
iptables -A FORWARD -p tcp --dport 80 -d <router_ip> -m string --string "/goform/" --algo bm -j DROP