CVE-2026-4491: Tenda A18 Pro Buffer Overflow Vulnerability

CVE-2026-4491 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda A18 Pro firmware version 02.03.02.28. The vulnerability exists in the fromSetIpMacBind function located in the /goform/SetIpMacBind file. Improper handling of the list argument allows attackers to trigger a stack-based buffer overflow condition. This vulnerability can be exploited remotely over the network, and exploit code has been publicly disclosed.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to potentially execute arbitrary code, crash the device, or gain unauthorized control over the affected Tenda A18 Pro router.

Affected Products

• Tenda A18 Pro firmware version 02.03.02.28

Discovery Timeline

• 2026-03-20 - CVE CVE-2026-4491 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2026-4491

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The fromSetIpMacBind function in the Tenda A18 Pro firmware fails to properly validate the length of user-supplied input through the list argument before copying it to a fixed-size stack buffer. When an attacker provides overly long input data, it overflows the allocated buffer space on the stack, potentially overwriting adjacent memory including return addresses and saved registers.

The network-accessible nature of this vulnerability significantly increases its risk profile, as exploitation does not require physical access to the device. Attackers with low-level privileges can remotely target the vulnerable endpoint at /goform/SetIpMacBind to trigger the overflow condition.

Root Cause

The root cause of CVE-2026-4491 is insufficient bounds checking in the fromSetIpMacBind function when processing the list parameter. The function allocates a fixed-size buffer on the stack to store user input but does not verify that the incoming data fits within this allocated space. This classic stack-based buffer overflow pattern allows memory corruption when oversized input is provided.

Attack Vector

Attackers can exploit this vulnerability by sending specially crafted HTTP requests to the /goform/SetIpMacBind endpoint on an affected Tenda A18 Pro device. The attack is network-based and requires low privileges to execute. By manipulating the list argument with excessive data, an attacker can overflow the stack buffer, potentially achieving code execution or causing denial of service.

The exploit has been publicly disclosed, making it accessible to potential threat actors. Organizations using affected devices should consider them at elevated risk until patched or mitigated.

Detection Methods for CVE-2026-4491

Indicators of Compromise

• Unusual HTTP POST requests to /goform/SetIpMacBind with abnormally large list parameter values
• Unexpected router reboots or crashes that may indicate exploitation attempts
• Network traffic anomalies targeting Tenda A18 Pro management interfaces
• Evidence of unauthorized configuration changes on affected devices

Detection Strategies

• Implement network intrusion detection rules to monitor for oversized HTTP requests to /goform/SetIpMacBind
• Deploy endpoint detection and response (EDR) solutions capable of identifying buffer overflow exploitation patterns
• Configure web application firewalls (WAF) to inspect and block requests with abnormal parameter lengths to Tenda device management endpoints
• Monitor router logs for access attempts to the vulnerable form handler

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic to Tenda router management interfaces
• Implement network segmentation to isolate IoT and network devices from untrusted networks
• Configure alerting for repeated failed authentication attempts or unusual access patterns to router administration pages

How to Mitigate CVE-2026-4491

Immediate Actions Required

• Restrict network access to the Tenda A18 Pro management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Place affected devices behind a properly configured firewall that blocks external access to the /goform/ endpoints
• Monitor for firmware updates from Tenda and apply patches as soon as they become available

Patch Information

As of the last modification date (2026-03-24), no official patch has been confirmed in the available CVE data. Users should monitor the Tenda Official Site for security updates and firmware releases addressing this vulnerability. Additional technical details and discussion can be found in the GitHub Issue Discussion and VulDB #352017.

Workarounds

• Configure firewall rules to block all external access to router management interfaces, allowing only connections from trusted internal networks
• If possible, use VLAN segmentation to isolate the management network from user and IoT networks
• Implement strong authentication mechanisms and change default credentials on all network devices
• Consider replacing vulnerable devices with alternatives that have active security support if no patch is released

# Example iptables rule to restrict access to router management interface
# Replace 192.168.1.0/24 with your trusted management network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP