CVE-2025-9935: Totolink N600r Firmware RCE Vulnerability

CVE-2025-9935 Overview

A command injection vulnerability has been identified in TOTOLINK N600R firmware version 4.3.0cu.7866_B20220506. This vulnerability affects the function sub_4159F8 within the file /web_cste/cgi-bin/cstecgi.cgi. By executing manipulation of input parameters, remote attackers can inject and execute arbitrary commands on the affected device. The exploit has been publicly disclosed, increasing the risk of exploitation in the wild.

Critical Impact

Remote unauthenticated attackers can execute arbitrary system commands on vulnerable TOTOLINK N600R routers, potentially leading to complete device compromise, network pivot attacks, and persistent unauthorized access.

Affected Products

• TOTOLINK N600R Firmware version 4.3.0cu.7866_B20220506
• TOTOLINK N600R Hardware

Discovery Timeline

• 2025-09-04 - CVE-2025-9935 published to NVD
• 2025-09-29 - Last updated in NVD database

Technical Details for CVE-2025-9935

Vulnerability Analysis

This command injection vulnerability exists in the TOTOLINK N600R router's web management interface. The vulnerable function sub_4159F8 in the CGI handler /web_cste/cgi-bin/cstecgi.cgi fails to properly sanitize user-supplied input before passing it to system commands. This weakness allows attackers to inject malicious shell commands that execute with the privileges of the web server process, typically root on embedded devices.

The vulnerability is classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) and CWE-77 (Improper Neutralization of Special Elements used in a Command). The attack can be executed remotely over the network without requiring any authentication or user interaction, making it particularly dangerous for internet-exposed devices.

Root Cause

The root cause of this vulnerability is improper input validation and sanitization in the sub_4159F8 function. The CGI script processes HTTP requests and directly incorporates user-controlled data into system command execution without adequate filtering of shell metacharacters. This allows special characters such as semicolons, backticks, and pipe operators to break out of the intended command context and execute attacker-supplied commands.

Attack Vector

The attack vector is network-based, targeting the web management interface of the TOTOLINK N600R router. An attacker can craft malicious HTTP requests to the /web_cste/cgi-bin/cstecgi.cgi endpoint with specially formatted parameters that inject shell commands. The vulnerability does not require authentication, meaning any attacker with network access to the management interface can exploit it.

The vulnerability mechanism involves manipulating input parameters to the vulnerable CGI function, allowing command injection through shell metacharacters. Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2025-9935

Indicators of Compromise

• Unusual outbound network connections from the router to unknown external IP addresses
• Unexpected processes running on the device that are not part of normal router operations
• Suspicious HTTP requests to /web_cste/cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, $(), backticks)
• Modified router configuration or unauthorized firmware changes

Detection Strategies

• Monitor network traffic for HTTP requests to TOTOLINK router CGI endpoints containing command injection patterns
• Implement intrusion detection rules to identify requests with shell metacharacters in parameters targeting cstecgi.cgi
• Deploy network behavior analysis to detect anomalous outbound connections from router IP addresses
• Review router logs for unexpected administrative access or configuration changes

Monitoring Recommendations

• Isolate TOTOLINK N600R devices on a separate network segment with restricted access
• Enable logging on upstream network devices to capture traffic to and from vulnerable routers
• Implement continuous vulnerability scanning to identify exposed TOTOLINK devices on your network
• Set up alerts for any access attempts to the web management interface from untrusted sources

How to Mitigate CVE-2025-9935

Immediate Actions Required

• Disable remote web management access to the TOTOLINK N600R router immediately
• Restrict management interface access to trusted internal IP addresses only using firewall rules
• Check for signs of compromise on affected devices and consider factory reset if suspicious activity is detected
• Monitor the TOTOLINK Official Website for firmware updates addressing this vulnerability

Patch Information

At the time of this writing, no official patch has been released by TOTOLINK for this vulnerability. Organizations should monitor vendor security advisories for updates. Additional vulnerability details are available through VulDB #322337.

Workarounds

• Disable the web management interface entirely if not required for device administration
• Implement network segmentation to isolate vulnerable devices from critical network assets
• Use a VPN or jump host for administrative access rather than exposing the management interface directly
• Consider replacing affected devices with alternative hardware from vendors with better security update practices

# Firewall rule example to restrict management interface access
# Block external access to router management port (typically 80/443)
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP