CVE-2023-42326: Netgate pfSense RCE Vulnerability

CVE-2023-42326 Overview

CVE-2023-42326 is a command injection vulnerability affecting Netgate pfSense and pfSense Plus firewall distributions. The vulnerability exists in the web-based management interface, specifically within the interfaces_gif_edit.php and interfaces_gre_edit.php components. A remote attacker with authenticated access to the web interface can exploit this flaw to execute arbitrary code on the underlying operating system by sending specially crafted requests to the vulnerable endpoints.

Critical Impact

Authenticated attackers can achieve full remote code execution on pfSense firewall appliances, potentially compromising network perimeter security and enabling lateral movement across protected networks.

Affected Products

• Netgate pfSense v.2.7.0 and prior versions
• Netgate pfSense Plus (affected versions)

Discovery Timeline

• 2023-11-14 - CVE CVE-2023-42326 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-42326

Vulnerability Analysis

This vulnerability is classified as CWE-77 (Command Injection), indicating that user-supplied input is improperly sanitized before being passed to system commands. The affected components handle GIF (Generic Interface Tunneling) and GRE (Generic Routing Encapsulation) tunnel interface configurations through the pfSense web interface.

When an authenticated administrator configures network tunnel interfaces through interfaces_gif_edit.php or interfaces_gre_edit.php, certain input parameters are processed without adequate validation or sanitization. This allows an attacker to inject arbitrary shell commands that are subsequently executed with the privileges of the web server process, which typically runs with elevated permissions on pfSense systems.

The attack requires network access to the pfSense web management interface and valid authentication credentials. Given that pfSense is commonly deployed as a perimeter firewall, successful exploitation could result in complete compromise of the network security infrastructure, including the ability to intercept traffic, modify firewall rules, or pivot to internal network segments.

Root Cause

The root cause of this vulnerability is insufficient input validation in the PHP scripts responsible for handling GIF and GRE tunnel interface configuration. User-supplied parameters are passed to underlying shell commands without proper sanitization, escaping, or parameterization. This allows attackers to break out of the intended command context and inject additional commands.

Attack Vector

The attack is network-based and requires low-privilege authenticated access to the pfSense web interface. An attacker must craft malicious HTTP requests to either the interfaces_gif_edit.php or interfaces_gre_edit.php endpoints with payloads containing shell metacharacters and commands. The vulnerability requires no user interaction beyond initial authentication, and successful exploitation grants the attacker command execution capabilities on the firewall system.

The attack flow involves:

1. Authenticating to the pfSense web interface with valid credentials
2. Navigating to the GIF or GRE interface configuration pages
3. Injecting malicious commands through vulnerable input parameters
4. The system processes the malicious input and executes the injected commands with elevated privileges

Detection Methods for CVE-2023-42326

Indicators of Compromise

• Unusual HTTP POST requests to /interfaces_gif_edit.php or /interfaces_gre_edit.php containing shell metacharacters (;, |, &&, backticks, $())
• Unexpected child processes spawned by the web server process (typically php-fpm or php-cgi)
• Anomalous outbound network connections originating from the pfSense firewall
• Unauthorized modifications to system files, user accounts, or firewall rules

Detection Strategies

• Implement web application firewall (WAF) rules to detect command injection patterns in requests to pfSense management interfaces
• Monitor authentication logs for unusual login patterns or access from unexpected IP addresses
• Deploy network-based intrusion detection signatures targeting requests to the vulnerable PHP endpoints
• Review system audit logs for process execution anomalies on pfSense appliances

Monitoring Recommendations

• Enable detailed logging for pfSense web interface access and review for suspicious activity
• Configure alerting for any administrative configuration changes to tunnel interfaces
• Monitor for reverse shell connections or unexpected outbound traffic from the firewall
• Establish baseline behavior patterns for the pfSense appliance to identify deviations

How to Mitigate CVE-2023-42326

Immediate Actions Required

• Upgrade pfSense to the latest patched version as indicated in the Netgate security advisory
• Restrict web interface access to trusted management networks only using firewall rules
• Implement multi-factor authentication for administrative access where possible
• Review access logs for any signs of prior exploitation attempts

Patch Information

Netgate has released a security advisory addressing this vulnerability. Administrators should consult the Netgate Security Advisory pfSense-SA-23_10 for detailed patch information and upgrade instructions. It is critical to apply the latest security updates to remediate this command injection flaw.

Additional technical details about this vulnerability and related pfSense security issues can be found in the SonarSource Blog on pfSense Vulnerabilities.

Workarounds

• Limit access to the pfSense web interface to specific trusted IP addresses using firewall rules
• Disable remote management access and only allow local console administration if feasible
• Place the management interface on a dedicated, isolated management VLAN
• Deploy additional network segmentation to limit the impact of potential firewall compromise
• Consider implementing a jump host or VPN requirement for accessing the management interface

If upgrading is not immediately possible, restricting network access to the management interface is the most effective temporary mitigation. Configure pfSense firewall rules to only allow connections to the web interface from specific administrator workstations or a dedicated management network segment.