CVE-2023-48123: Netgate pfSense RCE Vulnerability

CVE-2023-48123 Overview

CVE-2023-48123 is an input validation vulnerability affecting Netgate pfSense Plus v.23.05.1 and earlier, as well as pfSense CE v.2.7.0. This vulnerability allows remote attackers to execute arbitrary code via crafted requests to the packet_capture.php file within the pfSense web interface. The flaw stems from improper validation of user-supplied input parameters in the packet capture diagnostics functionality.

Critical Impact

Remote attackers with low-level authenticated access can exploit this vulnerability to achieve full system compromise, potentially gaining complete control over the firewall appliance and network infrastructure it protects.

Affected Products

• Netgate pfSense Plus v.23.05.1 and earlier versions
• Netgate pfSense CE v.2.7.0 and earlier versions
• Network appliances running vulnerable pfSense web GUI components

Discovery Timeline

• 2023-12-06 - CVE-2023-48123 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-48123

Vulnerability Analysis

This vulnerability exists in the packet capture diagnostic functionality within the pfSense web administration interface. The diag_packet_capture.php file fails to properly validate and sanitize user-supplied input for the count and length POST parameters before using them in system operations. Without proper validation, attackers can inject malicious values that break out of the intended context, leading to arbitrary code execution on the underlying system.

The attack requires network access to the pfSense web interface and basic authenticated access (low privileges). Once exploited, an attacker can achieve complete confidentiality, integrity, and availability impact on the targeted system—effectively taking full control of the firewall appliance.

Root Cause

The root cause of this vulnerability is insufficient input validation in the packet capture functionality. The original code directly used user-supplied POST parameters ($_POST['count'] and $_POST['length']) without verifying that they contain only numeric integer values. This allowed attackers to submit specially crafted non-numeric payloads that could be processed by the system in unintended ways, leading to command injection or code execution.

Attack Vector

The attack vector is network-based, requiring the attacker to submit malicious HTTP POST requests to the diag_packet_capture.php endpoint on the pfSense web interface. The attacker must have at least low-level authenticated access to the pfSense administration panel. By crafting a malicious request with specially formatted count or length parameters, an attacker can bypass the intended input handling and execute arbitrary code on the server.

// Security patch validating count and length parameters
// Source: https://github.com/pfsense/pfsense/commit/f72618c4abb61ea6346938d0c93df9078736b775

 	$input_filter = ($_POST['filter'] !== null) ? intval($_POST['filter']) : null;
 	if ($_POST['count'] == '0') {
 		$input_count = 0;
+	} elseif (empty($_POST['count'])) {
+		$input_count = 1000;
+	} elseif (!is_numericint($_POST['count'])) {
+		$input_error[] = 'Invalid Packet Count.';
 	} else {
-		$input_count = empty($_POST['count']) ? 1000 : $_POST['count'];
+		$input_count = intval($_POST['count']);
+	}
+	if (empty($_POST['length'])) {
+		$input_length = 0;
+	} elseif (!is_numericint($_POST['length'])) {
+		$input_error[] = 'Invalid Packet Length.';
+	} else {
+		$input_length = intval($_POST['length']);
 	}
-	$input_length = empty($_POST['length']) ? 0 : $_POST['length'];
 	$input_promiscuous = empty($_POST['promiscuous']) ? false : $_POST['promiscuous'];
 	// view options
 	$input_viewdetail = empty($_POST['viewdetail']) ? 'normal' : $_POST['viewdetail'];

The patch introduces proper validation using is_numericint() to ensure that only numeric integer values are accepted for the count and length parameters. Non-numeric input now generates an error message rather than being processed.

Detection Methods for CVE-2023-48123

Indicators of Compromise

• Unusual or malformed HTTP POST requests to /diag_packet_capture.php containing non-numeric values in count or length parameters
• Web server logs showing repeated or suspicious access patterns to the packet capture diagnostic endpoint
• Evidence of unauthorized command execution or shell spawning from the pfSense web server process
• Unexpected outbound network connections originating from the pfSense appliance

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block POST requests to diag_packet_capture.php containing non-numeric or excessively long values in count and length parameters
• Monitor pfSense web server access logs for abnormal patterns targeting diagnostic endpoints
• Deploy intrusion detection signatures to identify exploitation attempts against this specific vulnerability
• Review authentication logs for suspicious login activity preceding access to diagnostic functions

Monitoring Recommendations

• Enable comprehensive logging on pfSense web interface access, particularly for diagnostic and system administration pages
• Configure alerts for failed authentication attempts followed by successful logins to the pfSense admin panel
• Monitor system process creation on the pfSense appliance for unexpected child processes from the web server
• Implement network traffic analysis to detect anomalous outbound connections from firewall management interfaces

How to Mitigate CVE-2023-48123

Immediate Actions Required

• Update pfSense Plus to a version newer than v.23.05.1 that includes the security patch
• Update pfSense CE to a version newer than v.2.7.0 that includes the security patch
• Restrict access to the pfSense web administration interface to trusted networks and IP addresses only
• Review user accounts with access to the pfSense admin panel and remove unnecessary privileges

Patch Information

Netgate has released a security patch addressing this vulnerability. The fix is documented in Netgate Security Advisory pfSense-SA-23_11. The specific code changes implementing proper input validation can be reviewed in the GitHub commit f72618c4abb61ea6346938d0c93df9078736b775. Additional details are available in the pfSense issue tracker entry #14809.

Workarounds

• Implement network-level access controls to limit which IP addresses can reach the pfSense web interface
• Deploy a web application firewall in front of the pfSense management interface to filter malicious requests
• Disable direct internet access to the pfSense administration panel and require VPN for remote management
• Consider temporarily disabling the packet capture diagnostic feature if not actively needed until patching is complete

# Example: Restrict pfSense web interface access via firewall rules
# Add to pfSense firewall rules to limit admin interface access

# Allow management only from trusted admin network
pfctl -a "admin_access" -f - <<EOF
pass in on em0 proto tcp from 10.0.0.0/24 to any port 443
block in on em0 proto tcp from any to any port 443
EOF

# Verify current firewall rules
pfctl -a "admin_access" -sr