CVE-2025-13445: Tenda AC21 Buffer Overflow Vulnerability

CVE-2025-13445 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC21 router firmware version 16.03.08.16. The flaw exists in the /goform/SetIpMacBind endpoint, where improper handling of the list argument allows attackers to overflow a stack buffer. This vulnerability can be exploited remotely over the network, enabling attackers to potentially execute arbitrary code or crash the affected device. The exploit has been publicly disclosed and proof-of-concept materials are available.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially gain code execution on vulnerable Tenda AC21 routers, compromising network infrastructure security.

Affected Products

• Tenda AC21 Firmware version 16.03.08.16
• Tenda AC21 Hardware

Discovery Timeline

• 2025-11-20 - CVE-2025-13445 published to NVD
• 2026-02-24 - Last updated in NVD database

Technical Details for CVE-2025-13445

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the web management interface of the Tenda AC21 router, specifically within the /goform/SetIpMacBind endpoint. When processing the list parameter, the firmware fails to properly validate the length of user-supplied input before copying it into a fixed-size stack buffer. This boundary condition error allows an attacker to write beyond the allocated buffer space, corrupting adjacent memory on the stack.

The network-accessible attack vector combined with low attack complexity makes this vulnerability particularly concerning for environments where these routers are deployed. An attacker with low privileges can remotely trigger the overflow without any user interaction required.

Root Cause

The root cause of this vulnerability is insufficient input validation in the firmware's handling of the list argument within the IP-MAC binding functionality. The affected code path fails to implement proper bounds checking before copying user-controlled data into a stack-allocated buffer. This memory safety violation is a common pattern in embedded device firmware where resource constraints may lead developers to skip defensive programming practices.

Attack Vector

The attack vector is network-based, targeting the HTTP/HTTPS web management interface of the Tenda AC21 router. An attacker can craft a malicious HTTP request to the /goform/SetIpMacBind endpoint with an oversized list parameter value. When the vulnerable firmware processes this request, the excessive data overwrites the stack, potentially allowing the attacker to:

1. Overwrite return addresses to redirect execution flow
2. Inject and execute arbitrary shellcode
3. Cause denial of service through application crash

The vulnerability requires low-level privileges to exploit, suggesting that basic authentication to the router's web interface may be necessary. However, given the prevalence of default credentials on consumer routers, this barrier is often minimal in practice.

For detailed technical analysis of this vulnerability, refer to the GitHub Vulnerability Documentation and VulDB Entry #333017.

Detection Methods for CVE-2025-13445

Indicators of Compromise

• Unusual HTTP POST requests to /goform/SetIpMacBind containing abnormally large list parameter values
• Router crashes or unexpected reboots without administrative intervention
• Anomalous network traffic patterns originating from the router's management interface
• Evidence of unauthorized configuration changes to IP-MAC binding settings

Detection Strategies

• Monitor web server logs for HTTP requests to /goform/SetIpMacBind with payload sizes exceeding normal operational parameters
• Implement network-based intrusion detection rules to identify buffer overflow attempt patterns in HTTP traffic to Tenda devices
• Deploy application-layer firewalls to inspect and filter malformed requests targeting vulnerable endpoints
• Utilize behavioral analysis to detect abnormal router process crashes or memory access violations

Monitoring Recommendations

• Enable verbose logging on network perimeter devices to capture traffic to and from Tenda router management interfaces
• Configure alerts for multiple failed authentication attempts followed by successful access to goform endpoints
• Monitor for outbound connections from the router to unexpected external destinations that may indicate post-exploitation activity
• Periodically verify firmware integrity using hash comparison against known-good firmware images

How to Mitigate CVE-2025-13445

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not explicitly required for operations
• Change default administrator credentials to strong, unique passwords
• Segment the network to isolate affected Tenda routers from critical infrastructure
• Monitor for firmware updates from Tenda and apply patches immediately when available

Patch Information

As of the last NVD update on 2026-02-24, no official patch information has been published by the vendor. Organizations should monitor Tenda's Official Website for security advisories and firmware updates addressing this vulnerability. Given the public availability of exploit information documented on VulDB, prompt remediation action is strongly recommended.

Workarounds

• Implement network access control lists (ACLs) to limit management interface access to specific administrative workstations
• Place vulnerable routers behind a firewall that filters and inspects HTTP traffic to goform endpoints
• Consider replacing affected Tenda AC21 devices with alternative router hardware if patches are not forthcoming
• Deploy a Web Application Firewall (WAF) rule to block requests with oversized parameters to SetIpMacBind

# Example: iptables rules to restrict management access (apply on upstream firewall)
# Allow management access only from trusted admin subnet
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
# Block all other management access
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP