CVE-2024-0296: Totolink N200RE Firmware RCE Vulnerability

CVE-2024-0296 Overview

A critical OS command injection vulnerability has been identified in the Totolink N200RE router firmware version 9.3.5u.6139_B20201216. This vulnerability exists in the NTPSyncWithHost function within the /cgi-bin/cstecgi.cgi file, where improper handling of the host_time argument allows attackers to inject and execute arbitrary operating system commands. The vulnerability can be exploited remotely without authentication, potentially leading to complete device compromise.

Critical Impact

Remote attackers can execute arbitrary OS commands on affected Totolink N200RE routers without authentication, potentially gaining full control of the device and using it as a pivot point for further network attacks.

Affected Products

• Totolink N200RE Firmware version 9.3.5u.6139_B20201216
• Totolink N200RE hardware device

Discovery Timeline

• 2024-01-08 - CVE-2024-0296 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-0296

Vulnerability Analysis

This command injection vulnerability resides in the network time protocol synchronization functionality of the Totolink N200RE router. The NTPSyncWithHost function in /cgi-bin/cstecgi.cgi fails to properly sanitize user-supplied input in the host_time parameter before passing it to system shell commands. This allows an attacker to append malicious shell commands that will be executed with the privileges of the web server process, typically root on embedded devices.

The vulnerability is particularly dangerous because it requires no authentication to exploit. An attacker with network access to the router's web interface can craft malicious HTTP requests to trigger command execution. Given the nature of embedded device firmware, successful exploitation typically grants root-level access to the device operating system.

The exploit has been publicly disclosed and documented, increasing the risk of widespread exploitation. The vendor (Totolink) was contacted regarding this vulnerability but did not respond, leaving users without an official patch.

Root Cause

The root cause of CVE-2024-0296 is insufficient input validation and sanitization in the NTPSyncWithHost function. The host_time parameter is directly incorporated into a system command without proper escaping or validation of special characters. This classic CWE-78 (Improper Neutralization of Special Elements used in an OS Command) vulnerability allows shell metacharacters to break out of the intended command context and execute attacker-controlled commands.

Attack Vector

The attack is network-based and can be initiated remotely against the router's web management interface. An attacker crafts a malicious HTTP request to /cgi-bin/cstecgi.cgi targeting the NTPSyncWithHost function with a specially crafted host_time parameter containing shell metacharacters and malicious commands.

The exploitation flow involves:

1. Identifying a vulnerable Totolink N200RE device exposed on the network
2. Sending a crafted HTTP request to the CGI endpoint with shell injection payload in the host_time parameter
3. The injected commands execute on the device with elevated privileges
4. Attacker gains control of the router, potentially enabling further attacks on the connected network

Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2024-0296

Indicators of Compromise

• Unexpected outbound network connections from the router to unknown IP addresses
• Unusual processes running on the device (if accessible via SSH/Telnet)
• HTTP requests to /cgi-bin/cstecgi.cgi containing shell metacharacters (;, |, $(), backticks) in the host_time parameter
• Modified configuration files or firmware on the device
• Router exhibiting unexpected behavior such as DNS redirection or traffic interception

Detection Strategies

• Monitor HTTP traffic to /cgi-bin/cstecgi.cgi for requests containing shell injection patterns in POST parameters
• Implement network intrusion detection rules to flag command injection payloads targeting Totolink devices
• Review router logs for suspicious CGI requests or authentication anomalies
• Deploy network segmentation to isolate IoT and router management interfaces from untrusted networks

Monitoring Recommendations

• Enable logging on network firewalls to capture traffic to/from router management interfaces
• Implement continuous monitoring for unusual router behavior including unexpected DNS queries or connection attempts
• Regularly audit devices on the network to identify vulnerable Totolink N200RE firmware versions
• Monitor for exploitation attempts using threat intelligence feeds that track IoT vulnerabilities

How to Mitigate CVE-2024-0296

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Place the router's management interface behind a firewall or VPN to prevent remote exploitation
• Disable remote management functionality if not required
• Consider replacing the affected device with a supported alternative, as the vendor has not responded to disclosure
• Segment the network to limit the potential impact of a compromised router

Patch Information

No official patch is currently available from Totolink. The vendor was contacted regarding this vulnerability disclosure but did not respond. Users should implement the workarounds below and consider device replacement. Monitor VulDB Entry #249862 for any updates regarding vendor response or patches.

Workarounds

• Disable the web management interface entirely if not needed for device administration
• Implement access control lists (ACLs) on the network to restrict which hosts can reach the router's management port
• Use a dedicated management VLAN isolated from general network traffic
• Deploy a web application firewall (WAF) in front of the management interface to filter malicious requests
• Monitor and log all access attempts to the router's CGI interfaces for forensic purposes

# Example: Restrict management interface access using iptables on upstream device
# Block external access to router management interface (example IP: 192.168.1.1)
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow only trusted management host (example: 192.168.1.100)
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT