CVE-2025-52221: Tenda AC6 Buffer Overflow Vulnerability

CVE-2025-52221 Overview

CVE-2025-52221 is a buffer overflow vulnerability in the Tenda AC6 wireless router running firmware version 15.03.05.16_multi. The flaw exists in the formSetCfm function, which improperly handles the funcname, funcpara1, and funcpara2 parameters. Unauthenticated attackers can send crafted requests over the network to overflow stack or heap buffers, resulting in remote code execution or device crash. The vulnerability maps to CWE-787 Out-of-Bounds Write and CWE-120 Classic Buffer Overflow. The attack requires no privileges and no user interaction, making it directly exploitable against any reachable device.

Critical Impact

Unauthenticated network attackers can trigger memory corruption in the router's web management service to execute arbitrary code or disrupt network availability.

Affected Products

• Tenda AC6 router (hardware version 1.0)
• Tenda AC6 firmware 15.03.05.16_multi
• Deployments exposing the router web management interface to untrusted networks

Discovery Timeline

• 2026-04-08 - CVE-2025-52221 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2025-52221

Vulnerability Analysis

The Tenda AC6 web management binary exposes the formSetCfm handler to process configuration callback requests. The handler reads attacker-controlled values from the funcname, funcpara1, and funcpara2 HTTP parameters and copies them into fixed-size buffers without enforcing length limits. Because the device runs the affected service with elevated privileges on the embedded Linux system, successful exploitation typically yields full control of the router. An attacker can pivot from a compromised device to intercept traffic, alter DNS settings, or stage attacks against internal hosts.

Root Cause

The root cause is missing input validation on parameters consumed by formSetCfm. The function relies on unsafe string copy operations and trusts the length of values supplied through the web interface. When parameter content exceeds the destination buffer, adjacent stack or heap memory is overwritten, corrupting saved return addresses or control structures. The combination of CWE-120 and CWE-787 indicates both an oversized copy and a resulting out-of-bounds write.

Attack Vector

Exploitation occurs over the network against the router's HTTP management service. An attacker submits a POST or GET request to the endpoint backed by formSetCfm with oversized values in any of the three vulnerable parameters. No authentication is required, and the attacker does not need physical proximity if the management interface is reachable from the WAN or a compromised internal host. Public technical analysis is available in the GitHub IoT Vulnerability Details writeup and the broader GitHub IoT Vulnerability Collection.

No verified public exploit code is referenced in the available data. The vulnerability mechanism is described in the linked technical writeup.

Detection Methods for CVE-2025-52221

Indicators of Compromise

• HTTP requests to the router's management interface containing unusually long funcname, funcpara1, or funcpara2 parameter values
• Unexpected reboots, watchdog resets, or crash logs from the AC6 web service
• Outbound connections from the router to unfamiliar hosts following inbound management traffic
• Configuration changes such as altered DNS, admin credentials, or remote management settings without administrator action

Detection Strategies

• Inspect network traffic to the router for HTTP requests targeting formSetCfm with parameter lengths exceeding typical configuration values
• Alert on management interface access originating from WAN-side IP addresses
• Correlate router availability loss with preceding HTTP POST activity to administrative endpoints

Monitoring Recommendations

• Forward router syslog and crash data to a centralized logging platform for review
• Monitor DHCP and DNS configuration drift on the AC6 to detect post-exploitation tampering
• Track new or anomalous client devices appearing on the LAN that could indicate attacker pivoting

How to Mitigate CVE-2025-52221

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal hosts and disable WAN-side administration
• Place the affected device behind a network segmentation boundary that limits exposure of the HTTP service
• Replace end-of-support Tenda AC6 hardware if no vendor patch is available for firmware 15.03.05.16_multi
• Rotate administrator credentials and review configuration for unauthorized changes

Patch Information

No vendor advisory or fixed firmware version is referenced in the available CVE data. Administrators should monitor Tenda's official support channels for an updated firmware release addressing the formSetCfm parameter handling.

Workarounds

• Disable remote web management on the WAN interface
• Apply ACLs on upstream firewalls to block inbound TCP traffic to the router's management ports
• Isolate the AC6 on a dedicated VLAN to contain potential compromise
• Replace the device with a supported router model where business requirements demand internet-exposed management

# Example firewall rule to block external access to router management (Linux iptables)
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -i <wan_interface> -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -i <wan_interface> -j DROP