CVE-2025-52221: Tenda AC6 Buffer Overflow Vulnerability

CVE-2025-52221 Overview

CVE-2025-52221 is a buffer overflow vulnerability affecting Tenda AC6 wireless routers running firmware version 15.03.05.16_multi. The vulnerability exists in the formSetCfm function and can be triggered through the funcname, funcpara1, and funcpara2 parameters. This firmware vulnerability in consumer IoT networking equipment could allow attackers to compromise the integrity of affected devices.

Critical Impact

Buffer overflow in Tenda AC6 router firmware may allow attackers to execute arbitrary code or cause denial of service conditions on affected devices through maliciously crafted input parameters.

Affected Products

• Tenda AC6 Router Firmware Version 15.03.05.16_multi

Discovery Timeline

• April 8, 2026 - CVE-2025-52221 published to NVD
• April 8, 2026 - Last updated in NVD database

Technical Details for CVE-2025-52221

Vulnerability Analysis

This firmware vulnerability affects the formSetCfm function within the Tenda AC6 router's web management interface. The function fails to properly validate the length of user-supplied input before copying it into fixed-size memory buffers. When an attacker provides excessively long strings through the vulnerable parameters, the data overflows the allocated buffer space, potentially corrupting adjacent memory regions.

The affected parameters—funcname, funcpara1, and funcpara2—accept user input without adequate bounds checking. This represents a classic buffer overflow condition common in embedded IoT devices where memory constraints and legacy code practices often lead to insufficient input validation.

Root Cause

The root cause of CVE-2025-52221 is improper input validation within the formSetCfm function. The function accepts string parameters (funcname, funcpara1, funcpara2) and copies them into stack or heap buffers without verifying that the input length does not exceed the destination buffer size. This allows an attacker to write beyond the intended memory boundaries, potentially overwriting return addresses, function pointers, or other critical data structures.

Attack Vector

An attacker with network access to the Tenda AC6 router's web management interface can exploit this vulnerability by sending HTTP requests containing oversized values in the funcname, funcpara1, or funcpara2 parameters to the formSetCfm endpoint. Successful exploitation could allow the attacker to crash the device, cause a denial of service, or potentially achieve arbitrary code execution depending on the specific memory layout and available exploit mitigations.

The vulnerability is accessible through the router's web interface, which may be exposed to local network users by default. If remote management is enabled, the attack surface extends to internet-based attackers.

Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2025-52221

Indicators of Compromise

• Unusual HTTP POST requests to the router's web interface containing abnormally long parameter values in funcname, funcpara1, or funcpara2 fields
• Unexpected router reboots or crashes that may indicate exploitation attempts
• Network traffic anomalies suggesting command and control communications originating from the router device
• Modified router configuration settings or firmware that the administrator did not authorize

Detection Strategies

• Monitor network traffic for HTTP requests to Tenda AC6 management interfaces containing oversized parameter values
• Implement network-based intrusion detection rules to identify buffer overflow exploitation patterns targeting IoT devices
• Deploy network segmentation to isolate IoT devices and enable focused monitoring of traffic to and from router management interfaces
• Review router access logs for unusual authentication attempts or configuration change requests

Monitoring Recommendations

• Enable logging on network security devices to capture traffic to and from Tenda router management interfaces
• Implement continuous firmware version monitoring to ensure devices are running the latest available patches
• Configure alerts for unexpected router behavior including crashes, reboots, or configuration changes
• Consider deploying a network monitoring solution capable of detecting anomalous IoT device behavior

How to Mitigate CVE-2025-52221

Immediate Actions Required

• Disable remote management access to the Tenda AC6 router if not required for business operations
• Restrict access to the router's web management interface to trusted administrator IP addresses only
• Place the Tenda AC6 router behind a firewall that blocks unauthorized access to management interfaces
• Monitor for firmware updates from Tenda and apply patches as soon as they become available
• Consider replacing the affected device with a router from a vendor with a stronger security update commitment

Patch Information

At the time of publication, no vendor patch has been confirmed for this vulnerability. Administrators should monitor Tenda's official support channels and the GitHub IoT Vulnerability Collection for updates regarding fixes for firmware version 15.03.05.16_multi.

SentinelOne customers benefit from Singularity platform's network detection capabilities that can identify exploitation attempts and anomalous device behavior on managed networks.

Workarounds

• Disable the web management interface if device configuration changes are not frequently required
• Configure firewall rules to block external access to the router's management ports (typically port 80/443)
• Implement network segmentation to isolate the affected router from critical network resources
• Use a VPN for any required remote administration rather than exposing the management interface directly