CVE-2025-4849: Totolink N300rh Firmware RCE Vulnerability

CVE-2025-4849 Overview

A critical command injection vulnerability has been identified in TOTOLINK N300RH firmware version 6.1c.1390_B20191101. The vulnerability exists in the CloudACMunualUpdateUserdata function within the /cgi-bin/cstecgi.cgi file. Improper handling of the url argument allows attackers to inject arbitrary operating system commands, potentially leading to complete device compromise. The vulnerability can be exploited remotely by authenticated attackers, and exploit information has been publicly disclosed.

Critical Impact

Successful exploitation allows remote attackers to execute arbitrary commands on the affected TOTOLINK router, potentially leading to complete device takeover, network compromise, and use of the device for further attacks within the network.

Affected Products

• TOTOLINK N300RH Firmware version 6.1c.1390_B20191101
• TOTOLINK N300RH hardware devices running vulnerable firmware

Discovery Timeline

• 2025-05-18 - CVE-2025-4849 published to NVD
• 2025-05-24 - Last updated in NVD database

Technical Details for CVE-2025-4849

Vulnerability Analysis

This vulnerability represents a classic command injection flaw (CWE-77) within embedded router firmware. The CloudACMunualUpdateUserdata function in the CGI binary fails to properly sanitize user-supplied input before incorporating it into system command execution. When the url parameter is processed, malicious payloads containing shell metacharacters or command separators can break out of the intended command context and execute arbitrary system commands with the privileges of the web server process—typically root on embedded devices.

The network-accessible nature of this vulnerability significantly increases its risk profile. Attackers with low-privilege access to the router's web interface can exploit this flaw without requiring physical access to the device. Given that routers often serve as network perimeter devices, successful exploitation could provide attackers with a strategic foothold for lateral movement and persistent network access.

Root Cause

The root cause is improper input validation and injection prevention (CWE-74) in the firmware's CGI handler. The url argument is passed to a system command or shell execution function without adequate sanitization or parameterization. This allows shell metacharacters such as ;, |, &, `, and $() to be interpreted by the underlying shell, enabling command injection.

Attack Vector

The attack is conducted remotely over the network by submitting a crafted HTTP request to the /cgi-bin/cstecgi.cgi endpoint. An authenticated attacker can manipulate the url parameter to include malicious command sequences that will be executed by the router's operating system.

The vulnerability mechanism involves sending specially crafted requests to the vulnerable CGI endpoint. When the CloudACMunualUpdateUserdata function processes the url parameter, it passes user input directly to a command execution context without proper sanitization. Attackers can leverage command separators or shell metacharacters to append arbitrary commands that execute with the web server's privileges, which is typically root on embedded Linux systems. For technical details, see the vulnerability disclosure on GitHub.

Detection Methods for CVE-2025-4849

Indicators of Compromise

• Unusual outbound network connections from the router to unknown external IP addresses
• Unexpected processes running on the router that are not part of normal firmware operation
• Modified configuration files or new user accounts created on the device
• HTTP request logs showing suspicious payloads with shell metacharacters in the url parameter targeting /cgi-bin/cstecgi.cgi

Detection Strategies

• Monitor HTTP traffic to /cgi-bin/cstecgi.cgi for requests containing shell metacharacters (;, |, &, `, $()) in the url parameter
• Implement network intrusion detection rules to identify command injection patterns in CGI requests
• Deploy behavioral analysis to detect unusual process spawning or network activity from router devices
• Review router logs for repeated authentication attempts followed by CGI access patterns

Monitoring Recommendations

• Enable comprehensive logging on network perimeter devices and forward logs to a centralized SIEM
• Configure alerts for any requests to vulnerable CGI endpoints containing known injection patterns
• Monitor for firmware integrity changes using file integrity monitoring where supported
• Establish baseline network behavior for routers and alert on deviations

How to Mitigate CVE-2025-4849

Immediate Actions Required

• Check if any TOTOLINK N300RH devices in your environment are running firmware version 6.1c.1390_B20191101
• Restrict administrative interface access to trusted networks or specific IP addresses only
• Disable remote management features if not required for operations
• Implement network segmentation to isolate affected devices from critical infrastructure
• Monitor the TOTOLINK official website for firmware updates

Patch Information

At the time of publication, no vendor patch has been confirmed for this vulnerability. Organizations should monitor the TOTOLINK official website for security updates. Additional technical information is available through VulDB #309320.

Workarounds

• Restrict access to the router's web management interface to trusted internal networks only
• Implement firewall rules to block external access to port 80/443 on affected devices
• Consider deploying a web application firewall (WAF) in front of the management interface to filter malicious requests
• If the device must be internet-accessible, place it behind a VPN and require VPN authentication before management access

# Example iptables rules to restrict management interface access
# Allow management access only from trusted network
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
# Drop all other management access attempts
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP