CVE-2026-5350: Trendnet TEW-657BRM Buffer Overflow Flaw

CVE-2026-5350 Overview

A stack-based buffer overflow vulnerability has been discovered in the Trendnet TEW-657BRM wireless router firmware version 1.00.1. The vulnerability exists in the update_pcdb function within the /setup.cgi file, where improper handling of the mac_pc_dba argument allows attackers to trigger a buffer overflow condition. This flaw can be exploited remotely over the network, potentially allowing attackers to execute arbitrary code or cause denial of service on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially gain unauthorized access to the router, execute malicious code, or disrupt network services. The vendor has confirmed this product has been discontinued since June 23, 2011, and no security patches will be provided.

Affected Products

• Trendnet TEW-657BRM firmware version 1.00.1
• Trendnet TEW-657BRM (all versions - end of life product)

Discovery Timeline

• 2026-04-02 - CVE CVE-2026-5350 published to NVD
• 2026-04-02 - Last updated in NVD database

Technical Details for CVE-2026-5350

Vulnerability Analysis

This vulnerability represents a classic stack-based buffer overflow condition (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the update_pcdb function implemented in the router's web configuration interface at /setup.cgi. When processing the mac_pc_dba parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size buffer on the stack.

The network-accessible nature of this vulnerability is particularly concerning as it can be triggered remotely by any attacker who can reach the router's web management interface. Successful exploitation requires low-privilege authentication to the web interface, but once authenticated, an attacker can craft malicious input to overflow the stack buffer.

Stack-based buffer overflows in embedded devices like routers are especially dangerous because these devices often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization) or stack canaries that are common in desktop operating systems. This absence of security mitigations makes exploitation more reliable and increases the potential for arbitrary code execution.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the update_pcdb function when handling the mac_pc_dba argument. The function allocates a fixed-size buffer on the stack to store MAC address data but does not validate that the incoming data fits within this allocated space. When an attacker provides an overly long string for the mac_pc_dba parameter, the function writes beyond the buffer boundary, corrupting adjacent stack memory including potentially the return address and saved registers.

Attack Vector

The attack is network-based and targets the /setup.cgi endpoint on the router's web management interface. An attacker with low-level credentials can send a specially crafted HTTP request containing an oversized mac_pc_dba parameter value to trigger the overflow. The exploit has been publicly disclosed and proof-of-concept information is available, as noted in the GitHub vulnerability documentation.

The attack sequence involves:

1. Gaining access to the router's web management interface (typically requiring basic authentication)
2. Sending a malicious request to /setup.cgi with a crafted mac_pc_dba parameter
3. The oversized input overflows the stack buffer in update_pcdb
4. Depending on the payload, this can lead to code execution, system crash, or denial of service

For detailed technical information about this vulnerability, refer to the VulDB entry and the researcher's vulnerability documentation on GitHub.

Detection Methods for CVE-2026-5350

Indicators of Compromise

• Unusual or malformed HTTP requests to /setup.cgi containing excessively long mac_pc_dba parameter values
• Router crashes or unexpected reboots without clear cause
• Anomalous network traffic originating from the router's management interface
• Evidence of unauthorized configuration changes on the device

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for requests containing abnormally long parameter values in the mac_pc_dba field
• Deploy network intrusion detection systems (IDS) with signatures for buffer overflow attempts targeting CGI endpoints
• Configure alerts for repeated authentication attempts followed by large POST requests to /setup.cgi
• Implement web application firewall rules to block requests with parameter lengths exceeding expected MAC address formats

Monitoring Recommendations

• Enable logging on the router's web interface (if supported) to capture requests to /setup.cgi
• Monitor network segments where vulnerable devices reside for suspicious traffic patterns
• Conduct regular asset inventory scans to identify any TEW-657BRM devices still in production environments
• Review network traffic logs for connections to the router's administrative ports (typically TCP 80/443)

How to Mitigate CVE-2026-5350

Immediate Actions Required

• Immediately identify and inventory all Trendnet TEW-657BRM devices in your network environment
• Disconnect vulnerable devices from the network or isolate them behind additional firewalls
• Replace end-of-life TEW-657BRM routers with currently supported networking equipment
• Restrict access to the router's web management interface to trusted IP addresses only
• Consider disabling the web management interface entirely if remote management is not required

Patch Information

No security patch is available for this vulnerability. Trendnet has confirmed that the TEW-657BRM product has been discontinued and end-of-life since June 23, 2011 (over 14 years ago). The vendor has stated they are no longer providing support for this product and cannot confirm vulnerabilities. Trendnet has indicated they will make an announcement on their website's product support page and notify customers who registered their products.

Given the lack of vendor support, the only effective mitigation is to replace the affected device with a currently supported router model. For additional details, see the VulDB submission and VulDB CTI information.

Workarounds

• Disable remote management access to the router's web interface if not strictly required
• Place the router behind a firewall that restricts access to management ports from untrusted networks
• Implement network segmentation to isolate the vulnerable router from critical network assets
• Use access control lists (ACLs) to limit which IP addresses can reach the management interface
• Replace the device with a modern, supported router as soon as possible

# Example: Firewall rule to restrict access to router management interface
# Replace 192.168.1.1 with your router's IP and adjust trusted_network accordingly
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s ! trusted_network -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -s ! trusted_network -j DROP