CVE-2026-5353: Trendnet TEW-657BRM RCE Vulnerability

CVE-2026-5353 Overview

A command injection vulnerability has been identified in the Trendnet TEW-657BRM router firmware version 1.00.1. The vulnerability exists within the ping_test function of the /setup.cgi file, where improper sanitization of the c4_IPAddr parameter allows attackers to inject arbitrary operating system commands. This flaw enables remote attackers with low privileges to execute malicious commands on the affected device over the network.

Critical Impact

Remote attackers can exploit this OS command injection vulnerability to execute arbitrary commands on the router, potentially leading to complete device compromise, network reconnaissance, or use of the device as a pivot point for further attacks. The exploit is publicly available, increasing the risk of active exploitation.

Affected Products

• Trendnet TEW-657BRM firmware version 1.00.1
• Note: This product has been discontinued and end-of-life since June 23, 2011

Discovery Timeline

• April 2, 2026 - CVE-2026-5353 published to NVD
• April 2, 2026 - Last updated in NVD database

Technical Details for CVE-2026-5353

Vulnerability Analysis

This vulnerability is classified as CWE-77 (Improper Neutralization of Special Elements used in a Command - Command Injection). The ping_test function within the router's web interface (/setup.cgi) fails to properly sanitize user-supplied input in the c4_IPAddr parameter before passing it to system commands.

When a user submits a ping test request through the router's administrative interface, the c4_IPAddr parameter value is incorporated directly into a shell command without adequate input validation or escaping. This allows an attacker to append shell metacharacters and additional commands to the expected IP address input, resulting in arbitrary command execution with the privileges of the web server process running on the device.

The vulnerability can be exploited remotely over the network by authenticated users with low-level privileges. Given that the exploit is publicly available and documented, the barrier to exploitation is relatively low for attackers who have access to the device's administrative interface.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization in the ping_test function. The c4_IPAddr parameter is directly concatenated into a shell command without proper escaping or validation of the input format. The application fails to:

1. Validate that the input conforms to a valid IP address or hostname format
2. Escape or remove shell metacharacters (such as ;, |, &, $, backticks)
3. Use parameterized command execution methods that prevent injection

Attack Vector

The attack is conducted over the network through the router's web-based administration interface. An attacker with low-level authentication to the device can submit a crafted HTTP request to /setup.cgi containing the c4_IPAddr parameter with embedded shell commands.

For example, instead of providing a legitimate IP address, an attacker could inject command separators followed by arbitrary commands. The injected commands would then execute on the underlying Linux-based operating system with the privileges of the web server process.

The vulnerability mechanism involves the unsanitized parameter being passed to a system shell, where shell metacharacters are interpreted, allowing command chaining or substitution. Technical details and proof-of-concept information can be found in the GitHub Ping Test Documentation and VulDB #354706.

Detection Methods for CVE-2026-5353

Indicators of Compromise

• Unusual HTTP requests to /setup.cgi containing shell metacharacters in the c4_IPAddr parameter
• Unexpected outbound network connections from the router to external hosts
• Anomalous process execution or new network services running on the device
• Unauthorized configuration changes or firmware modifications

Detection Strategies

• Monitor web server logs for requests to /setup.cgi with suspicious patterns in query parameters
• Implement network-based intrusion detection rules to identify command injection patterns in HTTP traffic to router management interfaces
• Deploy honeypot configurations to detect reconnaissance attempts against legacy Trendnet devices
• Utilize SentinelOne Singularity for network visibility and threat detection across managed infrastructure

Monitoring Recommendations

• Enable verbose logging on network devices and forward logs to a centralized SIEM for analysis
• Implement alerting for any access attempts to administrative interfaces of legacy or end-of-life network devices
• Regularly audit network inventory to identify deprecated devices still in operation

How to Mitigate CVE-2026-5353

Immediate Actions Required

• Replace the affected Trendnet TEW-657BRM router with a currently supported device as soon as possible
• If immediate replacement is not feasible, disconnect the device from production networks
• Restrict administrative interface access to trusted management networks only using firewall rules
• Disable remote administration features if available in the device configuration

Patch Information

No security patch is available for this vulnerability. Trendnet has confirmed that the TEW-657BRM was discontinued on June 23, 2011, which is over 14 years ago. The vendor no longer provides support or security updates for this product. Trendnet has indicated they will make an announcement on their website's product support page and notify customers who registered their products.

Organizations using this device should prioritize hardware replacement with a currently supported network device. For additional information, refer to VulDB Submission #781566.

Workarounds

• Implement network segmentation to isolate the affected device from critical network assets
• Configure ACLs or firewall rules to restrict access to the router's web interface to specific trusted IP addresses only
• Disable the web administration interface entirely if alternative management methods are available
• Place the device behind a VPN-only accessible management network to limit exposure

# Example firewall rule to restrict management interface access (iptables)
# Allow only specific management IP to access router web interface
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s <trusted_mgmt_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP