CVE-2024-0297: Totolink N200RE Firmware RCE Vulnerability

CVE-2024-0297 Overview

CVE-2024-0297 is a critical OS command injection vulnerability affecting Totolink N200RE routers running firmware version 9.3.5u.6139_B20201216. The vulnerability exists in the UploadFirmwareFile function within the /cgi-bin/cstecgi.cgi endpoint, where improper handling of the FileName argument allows remote attackers to inject and execute arbitrary operating system commands on the affected device.

This vulnerability enables unauthenticated remote attackers to gain complete control over the affected router without any user interaction. The exploit has been publicly disclosed, and the vendor (Totolink) was contacted but did not respond to the disclosure.

Critical Impact

Unauthenticated remote attackers can execute arbitrary OS commands on vulnerable Totolink N200RE routers, potentially leading to complete device compromise, network infiltration, and use of the device in botnet operations.

Affected Products

• Totolink N200RE Firmware version 9.3.5u.6139_B20201216
• Totolink N200RE Router Hardware

Discovery Timeline

• 2024-01-08 - CVE-2024-0297 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-0297

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw resides in the firmware update functionality of the Totolink N200RE router, specifically within the UploadFirmwareFile function.

When processing firmware upload requests through the /cgi-bin/cstecgi.cgi endpoint, the application fails to properly sanitize or validate the FileName parameter before incorporating it into system commands. This allows attackers to append malicious shell commands that will be executed with the privileges of the web server process, typically running as root on embedded devices.

The network-accessible attack vector combined with no authentication requirements and no user interaction necessary makes this vulnerability particularly dangerous for internet-exposed devices.

Root Cause

The root cause of this vulnerability is insufficient input validation in the UploadFirmwareFile function. The FileName argument is directly passed to system shell commands without proper sanitization or escaping of special characters. This architectural flaw allows metacharacters such as semicolons, pipes, and backticks to break out of the intended command context and execute arbitrary commands.

Embedded device firmware often lacks proper input validation due to resource constraints and developer oversight, making command injection a common vulnerability class in IoT and router devices.

Attack Vector

The attack can be initiated remotely over the network by sending a crafted HTTP request to the /cgi-bin/cstecgi.cgi endpoint. An attacker manipulates the FileName parameter in the firmware upload request to include OS command injection payloads.

For example, an attacker could inject shell metacharacters followed by arbitrary commands in the filename parameter. The vulnerable function concatenates this unsanitized input into a system command, resulting in command execution. Common payloads might include commands to establish reverse shells, download additional malware, modify system configurations, or pivot to other network resources.

The vulnerability requires no authentication and no user interaction, allowing automated exploitation at scale. Technical details and proof-of-concept information are available in the GitHub PoC Repository and VulDB Entry #249863.

Detection Methods for CVE-2024-0297

Indicators of Compromise

• Unusual HTTP POST requests to /cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, `, $()) in the FileName parameter
• Unexpected outbound connections from the router to external IP addresses, particularly on non-standard ports
• New or modified files in the router's filesystem, especially in /tmp or writable directories
• Unusual processes running on the device such as shells, wget, curl, or netcat

Detection Strategies

• Deploy network-based intrusion detection systems (IDS) with rules to detect command injection patterns in HTTP traffic to /cgi-bin/cstecgi.cgi
• Monitor HTTP request logs for the affected endpoint with abnormal FileName parameter values containing shell special characters
• Implement web application firewalls (WAF) to filter requests containing OS command injection patterns
• Use SentinelOne Singularity to detect post-exploitation behaviors including suspicious process spawning and network connections from IoT devices

Monitoring Recommendations

• Enable logging on network perimeter devices to capture all traffic to and from affected Totolink routers
• Set up alerts for any access to the /cgi-bin/cstecgi.cgi endpoint from external IP addresses
• Monitor for DNS queries from the router to unknown or suspicious domains that may indicate command-and-control communication
• Regularly audit router configurations and firmware versions to identify vulnerable devices in your environment

How to Mitigate CVE-2024-0297

Immediate Actions Required

• Immediately restrict access to affected Totolink N200RE routers from untrusted networks by placing them behind a firewall
• Disable remote management interfaces if not required and limit access to the web administration interface to trusted internal networks only
• Consider replacing affected devices with alternatives from vendors with better security response practices
• Implement network segmentation to isolate IoT devices from critical network resources

Patch Information

As of the last update, Totolink has not responded to the vulnerability disclosure and no official patch is available. The vendor was contacted early about this disclosure but did not respond in any way. Organizations should monitor the VulDB CTI page for updates on vendor response.

Given the lack of vendor response, organizations should prioritize replacing affected devices or implementing strict compensating controls.

Workarounds

• Block external access to the router's web interface by configuring firewall rules to deny inbound connections on HTTP/HTTPS ports from untrusted networks
• If the device must remain in service, place it behind an additional firewall or reverse proxy that filters requests containing shell metacharacters
• Disable the firmware update functionality through the web interface if possible, or restrict access to the /cgi-bin/cstecgi.cgi endpoint via access control lists
• Consider deploying network access control (NAC) solutions to limit what devices can communicate with vulnerable routers

# Example iptables rules to restrict access to the router's web interface
# Apply on upstream firewall or router

# Allow management access only from trusted admin subnet
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT

# Block all other access to web interface
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP