CVE-2026-5351: Trendnet TEW-657BRM RCE Vulnerability

CVE-2026-5351 Overview

A command injection vulnerability has been identified in the Trendnet TEW-657BRM wireless router firmware version 1.00.1. The vulnerability exists in the add_wps_client function within the /setup.cgi file, where improper handling of the wl_enrolee_pin argument allows remote attackers to inject and execute arbitrary operating system commands. This vulnerability can be exploited remotely by authenticated attackers to gain unauthorized access to the underlying system.

Critical Impact

Remote attackers can execute arbitrary OS commands on the affected device, potentially leading to complete device compromise, network infiltration, and use as a pivot point for further attacks. Note that this product has been discontinued and unsupported since June 2011.

Affected Products

• Trendnet TEW-657BRM Firmware version 1.00.1
• End-of-life devices without vendor support

Discovery Timeline

• April 2, 2026 - CVE-2026-5351 published to NVD
• April 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5351

Vulnerability Analysis

This vulnerability stems from improper input validation in the add_wps_client function within the router's web-based management interface. The /setup.cgi script processes user-supplied input for the wl_enrolee_pin parameter without adequate sanitization, allowing shell metacharacters to be injected into system commands. When the WPS client addition functionality is invoked, the unsanitized PIN value is passed directly to underlying OS command execution, enabling command injection.

The vulnerability requires authentication to the router's web interface but can be exploited remotely from the network. Successful exploitation allows attackers to execute arbitrary commands with the privileges of the web server process, typically root on embedded devices. This vulnerability is classified under CWE-77 (Improper Neutralization of Special Elements used in a Command).

Root Cause

The root cause is insufficient input validation and lack of proper sanitization of the wl_enrolee_pin parameter before it is used in a system command execution context. The vulnerable function fails to properly escape or validate special characters, allowing shell command injection through crafted input values. This is a common flaw in embedded device firmware where user input is concatenated directly into shell command strings.

Attack Vector

The attack is network-based and requires the attacker to have valid credentials for the router's administrative interface. Once authenticated, an attacker can navigate to the WPS configuration functionality and submit a malicious value for the wl_enrolee_pin parameter. The crafted payload would typically include shell metacharacters such as semicolons, backticks, or command substitution syntax to break out of the intended command context and execute arbitrary commands.

The vulnerability mechanism involves injecting shell commands through the WPS PIN enrollment parameter. An attacker with authenticated access to the web interface can manipulate the wl_enrolee_pin argument by appending shell metacharacters followed by arbitrary commands. When the device processes this input, the commands are executed with the privileges of the web server process. For detailed technical information, refer to the GitHub vulnerability documentation.

Detection Methods for CVE-2026-5351

Indicators of Compromise

• Unusual outbound network connections from the router to external hosts
• Unexpected processes running on the device or modifications to system files
• Web server logs showing malformed or suspicious values in the wl_enrolee_pin parameter
• Evidence of command injection patterns in HTTP request logs (semicolons, backticks, pipes)

Detection Strategies

• Monitor HTTP traffic to /setup.cgi for suspicious input patterns containing shell metacharacters
• Implement network intrusion detection rules to identify command injection attempts targeting the WPS functionality
• Review access logs for authentication attempts followed by requests to WPS configuration endpoints
• Deploy network segmentation to isolate legacy IoT devices and monitor traffic anomalies

Monitoring Recommendations

• Enable comprehensive logging on network firewalls and intrusion detection systems
• Monitor for DNS queries or network connections that may indicate post-exploitation activity
• Implement alerting for any configuration changes or unusual administrative access to the device
• Conduct periodic network scans to identify vulnerable end-of-life devices still in operation

How to Mitigate CVE-2026-5351

Immediate Actions Required

• Replace the Trendnet TEW-657BRM with a currently supported router model immediately
• If replacement is not immediately possible, isolate the device from untrusted networks
• Restrict administrative interface access to trusted IP addresses only
• Disable remote management capabilities if enabled
• Change default credentials and use strong, unique passwords

Patch Information

No security patch is available for this vulnerability. The vendor has confirmed that the Trendnet TEW-657BRM 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 vulnerabilities. The vendor has committed to making an announcement on their website's product support page and notifying customers who registered their products.

Additional technical details are available through the VulDB vulnerability entry and GitHub documentation.

Workarounds

• Implement network-level access controls to restrict access to the router's management interface
• Place the device behind a firewall that filters incoming requests to /setup.cgi
• Disable WPS functionality if the device firmware allows
• Consider using a separate VLAN for IoT devices to limit lateral movement if compromised

# Example firewall rule to restrict management access (adapt to your environment)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP