CVE-2024-43392: Phoenix Contact TC mGuard RS4000 DoS Flaw

CVE-2024-43392 Overview

CVE-2024-43392 affects Phoenix Contact mGuard industrial security appliances across the FL MGUARD and TC MGUARD product families. A low-privileged remote attacker can manipulate the FW_INCOMING.FROM_IP, FW_INCOMING.IN_IP, FW_OUTGOING.FROM_IP, and FW_OUTGOING.IN_IP environment variables to alter firewall service configurations. This enables unauthorized changes to packet filtering, packet forwarding, network access control, and Network Address Translation (NAT) rules. The affected mGuard devices are commonly deployed in operational technology (OT) and industrial control system (ICS) environments as security gateways. Successful exploitation leads to denial-of-service conditions on downstream networks.

Critical Impact
A low-privileged remote attacker can modify firewall, NAT, and network access control rules on mGuard security gateways, disrupting protected industrial networks.

Affected Products

Phoenix Contact FL MGUARD series (CENTERPORT VPN-1000, CORE TX, DELTA TX/TX, GT/GT, PCI4000, PCIE4000, RS2000, RS2005, RS4000, RS4004, SMART2) firmware
Phoenix Contact TC MGUARD RS2000 3G/4G VPN and TC MGUARD RS4000 3G/4G VPN firmware
Phoenix Contact mGuard VPN-enabled variants across ATT, VZW, and standard carrier configurations

Discovery Timeline

2024-09-10 - CVE-2024-43392 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-43392

Vulnerability Analysis

The vulnerability is a code injection issue classified under [CWE-94]. Phoenix Contact mGuard firmware exposes firewall configuration state through environment variables consumed by internal service scripts. A low-privileged authenticated user can influence the FW_INCOMING.FROM_IP, FW_INCOMING.IN_IP, FW_OUTGOING.FROM_IP, and FW_OUTGOING.IN_IP values used by these routines. Because the values feed directly into firewall rule generation, an attacker can inject content that changes packet filter behavior, forwarding decisions, network access control, and NAT translations. The result is a denial-of-service condition affecting the networks the mGuard gateway is meant to protect.

Root Cause

The root cause is improper control over configuration values sourced from environment variables. Firewall rule generation logic accepts attacker-controlled input without adequate validation of the identity and privilege level of the caller. Because mGuard devices sit between untrusted and trusted network segments, any successful manipulation propagates into the data plane. The design assumption that only privileged administrative flows populate these variables is not enforced at runtime.

Attack Vector

Exploitation requires network reachability to the mGuard management interface and valid low-privileged credentials. No user interaction is required. An attacker submits crafted values for the affected environment variables through interfaces available to authenticated users. Once accepted, the firewall service applies the modified configuration, breaking legitimate traffic flows, disabling filtering, or misdirecting NAT'd sessions. The impact extends beyond the device to any industrial process depending on the traffic it mediates.

No verified public proof-of-concept code is available. See the VDE Security Advisory VDE-2024-039 for vendor technical details.

Detection Methods for CVE-2024-43392

Indicators of Compromise

Unexpected changes in mGuard firewall rules, NAT tables, or packet forwarding policies without a corresponding administrative change record
Configuration audit log entries showing modifications to FW_INCOMING.FROM_IP, FW_INCOMING.IN_IP, FW_OUTGOING.FROM_IP, or FW_OUTGOING.IN_IP from non-administrative accounts
Loss of connectivity or asymmetric routing between segments protected by an mGuard gateway

Detection Strategies

Baseline firewall and NAT configurations on each mGuard device and alert on deviations detected via scheduled configuration polling
Correlate authentication events from low-privileged mGuard accounts with subsequent configuration change events in the device audit trail
Monitor for atypical management-plane sessions targeting mGuard devices from OT jump hosts or engineering workstations

Monitoring Recommendations

Forward mGuard syslog and audit events to a central log platform and retain them for retrospective analysis
Alert on any successful configuration change performed by non-administrator roles on mGuard appliances
Track availability metrics for segments behind mGuard gateways to detect DoS conditions caused by rule tampering

How to Mitigate CVE-2024-43392

Immediate Actions Required

Apply the firmware update referenced in the VDE Security Advisory VDE-2024-039 to all affected FL MGUARD and TC MGUARD models
Restrict management-plane access to mGuard devices to a dedicated administrative network segment
Review all mGuard user accounts and remove or downgrade low-privileged accounts that are no longer needed
Capture and archive current known-good firewall, NAT, and access control configurations before remediation

Patch Information

Phoenix Contact has published remediation guidance through the VDE Security Advisory VDE-2024-039. Administrators should identify affected FL MGUARD and TC MGUARD hardware models in their inventory and apply the firmware versions listed in the advisory. Devices deployed in production OT environments should be patched during scheduled maintenance windows with rollback plans documented.

Workarounds

Enforce network access control lists that permit management access to mGuard devices only from authorized administrative hosts
Require multi-factor authentication or jump-host mediation for any account with mGuard console access
Segment low-privileged operational accounts away from any interface that allows firewall configuration input until firmware is updated

bash

# Configuration example: restrict mGuard management access at an upstream ACL
# Replace <MGUARD_MGMT_IP> and <ADMIN_JUMPHOST_IP> with site-specific values
access-list MGUARD_MGMT permit tcp host <ADMIN_JUMPHOST_IP> host <MGUARD_MGMT_IP> eq 443
access-list MGUARD_MGMT permit tcp host <ADMIN_JUMPHOST_IP> host <MGUARD_MGMT_IP> eq 22
access-list MGUARD_MGMT deny   ip any host <MGUARD_MGMT_IP> log