CVE-2026-5349: Trendnet TEW-657BRM Buffer Overflow Flaw

CVE-2026-5349 Overview

A stack-based buffer overflow vulnerability has been identified in the Trendnet TEW-657BRM wireless router firmware version 1.00.1. The vulnerability exists in the add_apcdb function within the /setup.cgi file, where improper handling of the mac_pc_dba argument allows an attacker to overflow the stack buffer. This vulnerability can be exploited remotely by authenticated attackers, potentially leading to arbitrary code execution on the affected device.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to potentially execute arbitrary code, compromise device integrity, and gain unauthorized access to the network router. The exploit is publicly available.

Affected Products

• Trendnet TEW-657BRM Firmware Version 1.00.1

Discovery Timeline

• 2026-04-02 - CVE-2026-5349 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-5349

Vulnerability Analysis

This vulnerability is a classic stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The add_apcdb function in /setup.cgi fails to properly validate the length of user-supplied input through the mac_pc_dba parameter before copying it to a fixed-size stack buffer. When an attacker provides an overly long input string, the data overwrites adjacent memory on the stack, potentially including the return address and other critical control flow data.

The attack is network-accessible and requires only low-level privileges to execute. The vulnerability affects confidentiality, integrity, and availability of the device, as successful exploitation could allow an attacker to execute arbitrary code with the privileges of the CGI process, typically running as root on embedded devices like this router.

It is important to note that the vendor has confirmed this product was discontinued and reached end-of-life on June 23, 2011—over 14 years ago. Trendnet has stated they no longer provide support for this product and cannot confirm the vulnerabilities, though they will notify registered customers via their website.

Root Cause

The root cause of this vulnerability is insufficient input validation in the add_apcdb function. The function accepts the mac_pc_dba parameter from user input via the CGI interface but does not properly validate or limit the size of the input before copying it to a stack-allocated buffer. This allows an attacker to provide more data than the buffer can hold, resulting in adjacent stack memory being overwritten.

This type of vulnerability is common in legacy embedded systems and firmware developed before modern secure coding practices became widespread. The lack of bounds checking, combined with the absence of stack protection mechanisms (such as stack canaries) in older embedded systems, makes this vulnerability particularly dangerous.

Attack Vector

The attack can be initiated remotely over the network. An attacker with low-level privileges (authenticated access to the router's web interface) can send a specially crafted HTTP request to the /setup.cgi endpoint with a malicious mac_pc_dba parameter value. The oversized input triggers the buffer overflow in the add_apcdb function.

The vulnerability mechanism works as follows: When the CGI script processes the request, it passes the mac_pc_dba argument to the vulnerable function. The function copies the input into a fixed-size stack buffer without proper length validation. By carefully crafting the payload, an attacker can overwrite the saved return address on the stack, redirecting program execution to attacker-controlled code.

For technical details regarding the exploitation methodology, refer to the vulnerability analysis on GitHub.

Detection Methods for CVE-2026-5349

Indicators of Compromise

• Unusual HTTP POST requests to /setup.cgi containing abnormally long mac_pc_dba parameter values
• Unexpected router reboots or crashes that may indicate exploitation attempts
• Unauthorized configuration changes on the router
• Abnormal outbound network traffic from the router indicating potential compromise

Detection Strategies

• Monitor web server logs for requests to /setup.cgi with excessively long parameter values
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting CGI endpoints
• Deploy SentinelOne Singularity™ for network visibility and anomaly detection on network segments containing legacy devices
• Establish baseline behavior for router administrative interfaces and alert on deviations

Monitoring Recommendations

• Enable logging on routers where possible and forward logs to a centralized SIEM for analysis
• Implement network segmentation to isolate legacy devices and monitor traffic crossing segment boundaries
• Conduct regular network scans to identify devices running vulnerable firmware versions
• Review authentication logs for the router's web interface for unusual access patterns

How to Mitigate CVE-2026-5349

Immediate Actions Required

• Replace the Trendnet TEW-657BRM with a supported router that receives regular security updates
• If immediate replacement is not possible, disable remote administration and restrict access to the web interface to trusted local networks only
• Implement network segmentation to isolate the vulnerable device from critical network resources
• Monitor network traffic to and from the device for signs of exploitation

Patch Information

No patch is available for this vulnerability. The vendor, Trendnet, has confirmed that the TEW-657BRM was discontinued and reached end-of-life on June 23, 2011. Trendnet no longer provides support for this product and will not be releasing a security update. Users are advised to replace the device with a currently supported model.

For additional details, refer to the VulDB entry and the vulnerability submission documentation.

Workarounds

• Disable remote management capabilities on the router to prevent remote exploitation
• Restrict access to the router's web interface using firewall rules, allowing only trusted IP addresses
• Place the router behind a properly configured firewall that can filter and inspect HTTP traffic
• Consider using a VPN to access the router's management interface instead of exposing it directly

# Network segmentation example using iptables to restrict access to router management
# Replace 192.168.1.1 with your router's IP and 192.168.1.100 with trusted admin workstation

# Allow management access only from trusted admin workstation
iptables -A FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP

# Block all external access to the router's web interface
iptables -A INPUT -i eth0 -d 192.168.1.1 -p tcp --dport 80 -j DROP