CVE-2025-9089: Tenda AC20 Buffer Overflow Vulnerability

CVE-2025-9089 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC20 router firmware version 16.03.08.12. This vulnerability exists in the sub_48E628 function within the /goform/SetIpMacBind endpoint. By manipulating the list argument, an attacker can trigger a stack-based buffer overflow condition that may lead to arbitrary code execution or denial of service on the affected device.

The vulnerability is network-accessible, meaning attackers can exploit it remotely without physical access to the device. A proof-of-concept exploit has been publicly disclosed, increasing the risk of exploitation in the wild.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash the router, compromising network security and availability.

Affected Products

• Tenda AC20 Router
• Tenda AC20 Firmware version 16.03.08.12

Discovery Timeline

• August 17, 2025 - CVE-2025-9089 published to NVD
• August 21, 2025 - Last updated in NVD database

Technical Details for CVE-2025-9089

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected function sub_48E628 fails to properly validate the length of user-supplied input passed through the list argument before copying it to a fixed-size stack buffer. This lack of bounds checking allows an attacker to supply an oversized payload that overwrites adjacent memory on the stack, including return addresses and other critical control data.

The vulnerability is particularly dangerous because it affects a network-facing endpoint (/goform/SetIpMacBind) designed for IP-MAC binding configuration. Since this functionality is accessible remotely, the attack surface is significant. The exploitation requires low-privilege authentication but no user interaction, making automated exploitation feasible.

Root Cause

The root cause of this vulnerability is improper input validation in the sub_48E628 function. When processing the list parameter from HTTP POST requests to /goform/SetIpMacBind, the function allocates a fixed-size buffer on the stack and copies user-supplied data without verifying that the input length does not exceed the buffer capacity. This classic programming error in embedded firmware allows attackers to overflow the stack buffer and corrupt adjacent memory regions.

Attack Vector

The attack vector is network-based, targeting the web management interface of the Tenda AC20 router. An attacker sends a crafted HTTP POST request to the /goform/SetIpMacBind endpoint with an oversized list parameter. The malicious payload overwrites the stack, potentially allowing the attacker to:

1. Crash the device (Denial of Service)
2. Hijack program execution flow by overwriting return addresses
3. Execute arbitrary code if the stack layout allows for reliable exploitation

The vulnerability can be exploited by sending specially crafted HTTP requests to the router's management interface. A proof-of-concept exploit has been documented in the GitHub Project Readme which demonstrates the exploitation technique. Technical details and a Python exploit script are also available for security researchers.

Detection Methods for CVE-2025-9089

Indicators of Compromise

• Unusual HTTP POST requests to /goform/SetIpMacBind with abnormally large list parameter values
• Router crashes or unexpected reboots without apparent cause
• Suspicious network traffic originating from the router's management interface
• Failed authentication attempts followed by requests to the vulnerable endpoint

Detection Strategies

• Monitor web server logs for POST requests to /goform/SetIpMacBind containing unusually long parameter values
• Implement network intrusion detection rules to identify oversized HTTP payloads targeting Tenda router management interfaces
• Deploy anomaly detection for traffic patterns indicating buffer overflow exploitation attempts
• Use SentinelOne Singularity to detect exploitation attempts and anomalous process behavior on network monitoring systems

Monitoring Recommendations

• Enable logging on network firewalls for all traffic to/from router management interfaces
• Implement rate limiting on the router's web management interface to slow potential exploitation attempts
• Monitor for unusual outbound connections from the router that may indicate successful compromise
• Regularly review access logs for the router's administrative interface

How to Mitigate CVE-2025-9089

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management access if not required
• Place the router's management interface behind a VPN or firewall
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability

Patch Information

As of the last update on August 21, 2025, no official patch has been released by Tenda. Organizations should monitor the vendor's official channels for security updates and apply patches immediately when available. Additional vulnerability details are tracked in VulDB #320357.

Workarounds

• Disable the web management interface entirely if not required for operations
• Implement network segmentation to isolate the router's management interface from untrusted networks
• Use access control lists (ACLs) to restrict which IP addresses can reach the management interface
• Consider replacing the affected device with a router from a vendor with a better security update track record

# Example: Restrict management interface access via iptables on upstream firewall
# Block external access to router management port (typically 80/443)
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 only trusted management hosts
iptables -I FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT