CVE-2024-12856: Four-faith F3x36 Firmware RCE Vulnerability

CVE-2024-12856 Overview

CVE-2024-12856 is an operating system (OS) command injection vulnerability affecting Four-Faith router models F3x24 and F3x36. The vulnerability exists in firmware version 2.0 and allows authenticated remote attackers to execute arbitrary OS commands over HTTP when modifying the system time via the apply.cgi endpoint. This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command).

The severity of this vulnerability is significantly amplified by the presence of default credentials in the affected firmware. If administrators have not changed these default credentials, the vulnerability effectively becomes an unauthenticated remote command execution issue, dramatically lowering the barrier to exploitation.

Critical Impact

Remote attackers can execute arbitrary operating system commands on vulnerable Four-Faith routers, potentially leading to complete device compromise, network pivoting, and persistent backdoor access. Default credentials make this exploitable without authentication.

Affected Products

• Four-Faith F3x36 Router (Firmware version 2.0)
• Four-Faith F3x36 Firmware
• Four-Faith F3x24 Router (Firmware version 2.0)
• Four-Faith F3x24 Firmware

Discovery Timeline

• 2024-12-27 - CVE-2024-12856 published to NVD
• 2025-09-25 - Last updated in NVD database

Technical Details for CVE-2024-12856

Vulnerability Analysis

This command injection vulnerability resides in the system time configuration functionality of Four-Faith routers. When users modify the system time through the web management interface, the router processes user-supplied input via the apply.cgi script without adequate sanitization. The improper handling of user input allows attackers to inject arbitrary shell commands that execute with the privileges of the web server process, typically root on embedded devices.

The attack can be conducted remotely over the network and requires minimal technical complexity. While the vulnerability officially requires authentication (high privileges in CVSS terms), the presence of default credentials in firmware version 2.0 means that many deployed devices may be vulnerable to unauthenticated attacks if administrators have not changed these credentials.

Root Cause

The root cause of CVE-2024-12856 is improper input validation and sanitization in the apply.cgi endpoint responsible for system time configuration. User-supplied parameters are passed directly to shell commands without proper escaping or validation, creating a classic OS command injection scenario. This is compounded by the insecure default configuration that ships with hardcoded credentials, violating secure-by-default design principles.

Attack Vector

The attack leverages the HTTP-based web management interface exposed by Four-Faith routers. An attacker can craft malicious HTTP requests to the apply.cgi endpoint, embedding OS commands within the time configuration parameters. The vulnerability is exploited through the network, and successful exploitation grants the attacker the ability to execute arbitrary commands on the underlying operating system.

The attack flow typically involves:

1. Identifying a vulnerable Four-Faith F3x24 or F3x36 router
2. Authenticating using default credentials (if unchanged) or valid credentials
3. Sending a crafted HTTP request to apply.cgi with injected commands in the system time parameter
4. Achieving command execution on the target device

Detailed technical analysis is available in the VulnCheck Blog and VulnCheck Security Advisory.

Detection Methods for CVE-2024-12856

Indicators of Compromise

• Unexpected HTTP POST requests to /apply.cgi containing shell metacharacters or command syntax in time-related parameters
• Unusual process spawning from the web server process on the router
• Network connections originating from the router to external command-and-control servers
• Modifications to system files, cron jobs, or startup scripts on the device
• Authentication logs showing successful logins using default credentials from external IP addresses

Detection Strategies

• Monitor HTTP traffic to Four-Faith router management interfaces for suspicious requests to apply.cgi endpoints
• Implement network segmentation to restrict access to router management interfaces from untrusted networks
• Deploy intrusion detection systems (IDS) with signatures for command injection patterns in HTTP traffic
• Review router logs for authentication attempts, especially those using default credentials
• Conduct regular vulnerability scans against network infrastructure devices

Monitoring Recommendations

• Enable and centralize logging for all Four-Faith router management interface access
• Monitor for outbound connections from router devices to unknown external hosts
• Set up alerts for multiple failed authentication attempts followed by successful logins
• Track changes to router configurations and system settings

How to Mitigate CVE-2024-12856

Immediate Actions Required

• Immediately change default credentials on all Four-Faith F3x24 and F3x36 routers
• Restrict access to the web management interface to trusted IP addresses only
• Place router management interfaces behind a VPN or on a dedicated management VLAN
• Disable remote management access if not required for operations
• Monitor for suspicious activity targeting router management interfaces

Patch Information

At the time of publication, no vendor patch information was available in the CVE data. Organizations should contact Four-Faith directly for firmware updates or security patches addressing this vulnerability. Monitor the VulnCheck Security Advisory for updates on patch availability.

Workarounds

• Implement strong, unique passwords for all router accounts to mitigate the default credential risk
• Use firewall rules to block access to the router's web management interface (apply.cgi) from untrusted networks
• Consider deploying a web application firewall (WAF) in front of management interfaces to filter malicious requests
• If possible, disable the web management interface entirely and manage devices through serial console or SSH
• Implement network monitoring to detect and alert on exploitation attempts

# Example: Restrict management interface access using iptables (if supported)
# Allow management access only from trusted admin 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
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP