CVE-2024-46538: Netgate pfSense XSS Vulnerability

CVE-2024-46538 Overview

A cross-site scripting (XSS) vulnerability has been identified in pfSense v2.5.2, a widely deployed open-source firewall and router distribution. The vulnerability exists in the interfaces_groups_edit.php file where attackers can execute arbitrary web scripts or HTML by injecting a crafted payload into the $pconfig variable. This stored XSS flaw could allow authenticated attackers with high privileges to compromise other administrative users accessing the affected interface.

Critical Impact

Attackers can inject malicious scripts into the pfSense web interface, potentially stealing session cookies, capturing credentials, or performing unauthorized actions on behalf of other administrators accessing the compromised page.

Affected Products

• Netgate pfSense version 2.5.2
• pfSense interface groups configuration module (interfaces_groups_edit.php)
• Web-based management interface

Discovery Timeline

• 2024-10-22 - CVE-2024-46538 published to NVD
• 2024-10-30 - Last updated in NVD database

Technical Details for CVE-2024-46538

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The flaw originates from insufficient input validation and output encoding in the interface groups editing functionality of pfSense.

The vulnerability requires an attacker to have high-level privileges (administrative access) to exploit, and also requires user interaction from another administrator viewing the compromised page. While the attack complexity is low once the prerequisites are met, the scope is changed, meaning the vulnerable component impacts resources beyond its security scope - allowing the attacker to potentially compromise other administrative sessions.

The impact includes potential confidentiality and integrity breaches through script execution in victim browsers, though availability is not directly affected.

Root Cause

The root cause of this vulnerability lies in improper sanitization of user-supplied input in the $pconfig variable within the interfaces_groups_edit.php file. When administrators configure interface groups through the web interface, the application fails to properly encode or sanitize certain input values before rendering them back to the page. This allows malicious JavaScript or HTML code to be stored and subsequently executed when the page is viewed.

Attack Vector

The attack is network-based and targets the pfSense web management interface. An attacker with administrative privileges can inject malicious scripts through the interface groups configuration page. When another administrator accesses or edits the compromised interface group configuration, the injected script executes within their browser context. This can lead to session hijacking, credential theft, or unauthorized administrative actions performed on behalf of the victim.

The exploitation flow typically involves:

1. Authenticated attacker with high privileges accesses the interface groups edit page
2. Attacker crafts a malicious payload containing JavaScript code
3. The payload is injected into a vulnerable parameter within the $pconfig variable
4. When another administrator views or edits the affected interface group, the malicious script executes
5. The attacker can capture session tokens, perform CSRF attacks, or redirect users to malicious sites

Detection Methods for CVE-2024-46538

Indicators of Compromise

• Unusual JavaScript code or HTML tags present in interface group names or descriptions
• Unexpected entries in pfSense configuration files containing script tags or event handlers
• Browser console errors or unexpected script execution when accessing interface groups pages
• Authentication logs showing suspicious activity following interface group configuration changes

Detection Strategies

• Monitor pfSense web server logs for requests to interfaces_groups_edit.php containing suspicious characters or encoded payloads
• Implement Content Security Policy (CSP) headers to detect and block inline script execution
• Review interface group configurations for entries containing HTML special characters (<, >, ", ')
• Deploy web application firewalls (WAF) with XSS detection rules to identify injection attempts

Monitoring Recommendations

• Enable detailed logging for pfSense web interface access and configuration changes
• Set up alerts for configuration modifications to interface groups from unexpected sources
• Monitor for outbound connections from the pfSense management interface to unknown external hosts
• Implement session monitoring to detect potential hijacking attempts following configuration page access

How to Mitigate CVE-2024-46538

Immediate Actions Required

• Restrict access to the pfSense web management interface to trusted networks only
• Limit administrative privileges to essential personnel and audit existing admin accounts
• Consider disabling the web interface and using console or SSH for critical configurations until patched
• Implement network segmentation to isolate management interfaces from general network traffic

Patch Information

Users should monitor the pfSense Issue Tracker for official patch information and updates. Additionally, technical documentation regarding this vulnerability is available at the GitHub XSS Documentation page. Upgrade to the latest version of pfSense when a patched release becomes available that addresses this XSS vulnerability.

Workarounds

• Implement strict Content Security Policy (CSP) headers to prevent inline script execution
• Use a reverse proxy with XSS filtering capabilities in front of the pfSense management interface
• Limit web interface access to specific IP addresses using firewall rules on the management interface
• Regularly audit interface group configurations for suspicious entries and remove any unauthorized content

# Configuration example - Restrict management interface access
# Add to pfSense firewall rules via System > Advanced > Admin Access
# Limit webConfigurator access to specific management subnet
# Example: Allow only 192.168.1.0/24 to access management interface

# Via SSH, review interface groups for suspicious content:
cat /cf/conf/config.xml | grep -A 10 "<ifgroups>"

# Enable HTTPS-only access and disable HTTP redirect
# Navigate to System > Advanced > Admin Access
# Set Protocol to HTTPS and disable HTTP redirect