CVE-2025-4851 Overview
A critical command injection vulnerability has been identified in the TOTOLINK N300RH wireless router firmware version 6.1c.1390_B20191101. This vulnerability exists within the setUploadUserData function located in the /cgi-bin/cstecgi.cgi file. Remote attackers can exploit this flaw by manipulating the FileName argument to inject and execute arbitrary operating system commands on the affected device.
Critical Impact
Remote attackers with network access can execute arbitrary commands on vulnerable TOTOLINK N300RH routers, potentially leading to complete device compromise, network infiltration, and persistent unauthorized access.
Affected Products
- TOTOLINK N300RH Firmware version 6.1c.1390_B20191101
- TOTOLINK N300RH Hardware
Discovery Timeline
- May 18, 2025 - CVE-2025-4851 published to NVD
- May 24, 2025 - Last updated in NVD database
Technical Details for CVE-2025-4851
Vulnerability Analysis
This vulnerability falls under CWE-77 (Command Injection) and CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component). The setUploadUserData function in the CGI binary fails to properly sanitize user-supplied input passed through the FileName parameter before incorporating it into system commands.
The vulnerability is exploitable remotely over the network with low attack complexity, though it requires some level of authentication. Successful exploitation allows attackers to execute arbitrary commands with the privileges of the web server process, typically running as root on embedded devices like this router.
Root Cause
The root cause of this vulnerability is insufficient input validation and sanitization in the setUploadUserData function. When processing the FileName argument, the function directly passes user-controlled data to system command execution functions without proper escaping or filtering of shell metacharacters. This allows attackers to break out of the intended command context and inject additional malicious commands.
Attack Vector
The attack vector is network-based, targeting the /cgi-bin/cstecgi.cgi endpoint on the router's web management interface. An authenticated attacker can craft a malicious HTTP request with a specially constructed FileName parameter containing shell metacharacters and command payloads. The vulnerability has been publicly disclosed, and technical details are available through the GitHub Documentation reference.
The exploitation mechanism involves injecting command separators (such as ;, |, or $()) followed by arbitrary commands into the FileName parameter. When the setUploadUserData function processes this input, the injected commands are executed on the underlying operating system.
Detection Methods for CVE-2025-4851
Indicators of Compromise
- Unusual HTTP POST requests to /cgi-bin/cstecgi.cgi containing shell metacharacters in the FileName parameter
- Unexpected outbound network connections from the router to unknown external IP addresses
- New or modified files in writable directories on the router filesystem
- Suspicious process spawning from the CGI handler or web server process
Detection Strategies
- Monitor HTTP traffic to the router's management interface for requests containing command injection patterns such as ;, |, &&, ||, or $() in POST parameters
- Implement network-based intrusion detection rules targeting the /cgi-bin/cstecgi.cgi endpoint with malformed or suspicious FileName values
- Deploy honeypot devices running vulnerable firmware versions to detect active exploitation attempts in your network
Monitoring Recommendations
- Enable logging on network perimeter devices to capture traffic destined for router management interfaces
- Implement alerting for any external network access to router administration ports (typically port 80 or 443)
- Regularly review router configuration and installed files for unauthorized modifications
- Monitor for DNS queries or network connections to known malicious infrastructure from IoT device network segments
How to Mitigate CVE-2025-4851
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal networks only
- Disable remote management access from WAN interfaces if enabled
- Implement network segmentation to isolate the router management interface from untrusted networks
- Monitor for exploitation attempts using the detection strategies outlined above
- Consider replacing end-of-life devices with currently supported hardware
Patch Information
At the time of publication, no official vendor patch has been released for this vulnerability. Users should check the TOTOLINK Homepage for firmware updates. The vulnerability affects firmware version 6.1c.1390_B20191101, and users should upgrade to a patched version when available.
Additional technical details and vulnerability information can be found through the VulDB entry #309322.
Workarounds
- Disable the web management interface entirely if not required for device administration
- Configure firewall rules to restrict access to the CGI endpoint from untrusted sources
- Place the router behind a properly configured network firewall that can filter malicious requests
- Use VPN access for remote administration instead of exposing the management interface directly
# Example iptables rules to restrict management interface access
# Apply these on an upstream firewall protecting the router
# Block external access to router management port
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP
# Allow only specific trusted management hosts
iptables -I FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
