CVE-2026-4493: Tenda A18 Pro Buffer Overflow Vulnerability

CVE-2026-4493 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 sub_423B50 function within the MAC Filtering Configuration Endpoint (/goform/setMacFilterCfg). An attacker can exploit this vulnerability by manipulating the deviceList argument, potentially leading to arbitrary code execution or denial of service. The vulnerability is remotely exploitable and has been publicly disclosed.

Critical Impact

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

Affected Products

• Tenda A18 Pro firmware version 02.03.02.28
• MAC Filtering Configuration Endpoint (/goform/setMacFilterCfg)
• Function sub_423B50 within the affected firmware

Discovery Timeline

• March 20, 2026 - CVE-2026-4493 published to NVD
• March 24, 2026 - Last updated in NVD database

Technical Details for CVE-2026-4493

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The affected function sub_423B50 fails to properly validate the length of user-supplied input in the deviceList parameter before copying it to a fixed-size stack buffer. When an attacker sends a specially crafted request with an oversized deviceList value to the /goform/setMacFilterCfg endpoint, the input overflows the allocated stack buffer, potentially overwriting adjacent memory including the return address.

The network-accessible nature of this vulnerability significantly increases its risk profile, as attackers can exploit it remotely without physical access to the device. The MAC Filtering Configuration Endpoint is part of the router's web management interface, which is typically accessible from the local network and sometimes exposed to the internet through misconfiguration.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the sub_423B50 function when processing the deviceList parameter. The function allocates a fixed-size buffer on the stack but does not validate whether the incoming data exceeds this buffer's capacity before performing the copy operation. This classic buffer overflow pattern allows attackers to write beyond the intended memory boundaries.

Attack Vector

The attack can be performed remotely over the network by sending a malicious HTTP POST request to the /goform/setMacFilterCfg endpoint. The attacker crafts a request containing an oversized deviceList parameter value designed to overflow the stack buffer. Successful exploitation requires low-privilege authenticated access to the web management interface.

The exploitation mechanism involves sending a carefully constructed payload through the MAC filtering configuration form. When the vulnerable function processes this malformed input, the stack buffer overflows, potentially allowing the attacker to control program execution flow. For detailed technical analysis, refer to the GitHub Issue Discussion where the vulnerability has been publicly documented.

Detection Methods for CVE-2026-4493

Indicators of Compromise

• Unusually large HTTP POST requests to /goform/setMacFilterCfg endpoint
• Unexpected device reboots or crashes after web interface access
• Abnormal network traffic patterns originating from the router
• Authentication logs showing repeated access to MAC filtering configuration

Detection Strategies

• Monitor HTTP traffic for requests to /goform/setMacFilterCfg with abnormally large deviceList parameters
• Implement network intrusion detection rules to flag oversized POST requests to Tenda device management endpoints
• Deploy application-layer firewalls to inspect and filter malicious payloads targeting known vulnerable endpoints
• Enable logging on network devices to capture and analyze suspicious configuration change attempts

Monitoring Recommendations

• Configure network monitoring tools to alert on unusual traffic patterns to Tenda devices
• Implement rate limiting on web management interface endpoints
• Enable comprehensive logging for all administrative access to network devices
• Review access logs regularly for signs of exploitation attempts or unauthorized configuration changes

How to Mitigate CVE-2026-4493

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management if not required for operations
• Implement network segmentation to isolate vulnerable devices from untrusted networks
• Monitor for exploitation attempts while awaiting vendor patches

Patch Information

As of the last update on March 24, 2026, no official patch has been released by Tenda. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Additional technical details and tracking information are available through VulDB #352019.

Workarounds

• Configure firewall rules to restrict access to the /goform/setMacFilterCfg endpoint from untrusted sources
• Use a VPN or jump host for administrative access to the device management interface
• Consider replacing vulnerable devices with alternative products until a patch is available
• Implement network access control lists (ACLs) to limit which hosts can communicate with the router's management interface

# Example iptables rules to restrict access to Tenda management interface
# Replace 192.168.1.1 with your router's IP and 192.168.1.100 with trusted admin host

# Block all external access to web management port
iptables -A INPUT -p tcp --dport 80 -d 192.168.1.1 -j DROP

# Allow only trusted admin host to access management interface
iptables -I INPUT -p tcp --dport 80 -s 192.168.1.100 -d 192.168.1.1 -j ACCEPT