CVE-2023-3596: Rockwell Automation 1756-EN4TR DoS Flaw

CVE-2023-3596 Overview

CVE-2023-3596 is an out-of-bounds write vulnerability affecting Rockwell Automation 1756-EN4* Ethernet/IP communication products. This vulnerability allows a malicious user to cause a denial of service condition by sending maliciously crafted Common Industrial Protocol (CIP) messages to the target system. The affected devices are critical components in industrial control system (ICS) environments, making this vulnerability particularly concerning for operational technology (OT) security.

Critical Impact

Exploitation of this vulnerability can disrupt industrial processes by causing denial of service on Rockwell Automation Ethernet/IP communication modules, potentially affecting manufacturing operations and critical infrastructure.

Affected Products

• Rockwell Automation 1756-EN4TR (and firmware)
• Rockwell Automation 1756-EN4TRK (and firmware)
• Rockwell Automation 1756-EN4TRXT (and firmware)

Discovery Timeline

• July 12, 2023 - CVE-2023-3596 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-3596

Vulnerability Analysis

The vulnerability is classified as CWE-787 (Out-of-bounds Write), which occurs when the software writes data past the end, or before the beginning, of the intended buffer. In the context of the Rockwell Automation 1756-EN4* Ethernet/IP modules, this flaw can be triggered through specially crafted CIP messages sent over the network. The out-of-bounds write condition leads to memory corruption, which ultimately causes the device to enter a fault state, resulting in denial of service.

The attack can be launched remotely without requiring authentication or user interaction. An attacker with network access to the vulnerable device can exploit this flaw to disrupt communications between programmable logic controllers (PLCs) and other industrial automation components.

Root Cause

The root cause of this vulnerability lies in improper boundary checking when processing CIP messages. The firmware fails to adequately validate the length or content of incoming CIP protocol messages, allowing an attacker to craft messages that cause the system to write data outside the bounds of allocated memory buffers. This memory corruption compromises the stability of the device, leading to assertion failures and denial of service.

Attack Vector

The attack vector is network-based, requiring the attacker to have network connectivity to the vulnerable Rockwell Automation 1756-EN4* module. The attack does not require any privileges or user interaction:

1. The attacker identifies a network-accessible 1756-EN4* Ethernet/IP module
2. Maliciously crafted CIP messages are constructed to trigger the out-of-bounds write condition
3. The messages are sent to the target device over the Ethernet/IP protocol (typically TCP port 44818)
4. The device processes the malformed messages, causing memory corruption
5. The system enters an assertion fault state, disrupting industrial communications

Due to the nature of the vulnerability and ICS/SCADA security best practices, no proof-of-concept code is provided. Organizations should refer to the Rockwell Automation Security Advisory for detailed technical information.

Detection Methods for CVE-2023-3596

Indicators of Compromise

• Unexpected device reboots or fault conditions on 1756-EN4* modules
• Anomalous CIP traffic patterns or malformed protocol messages targeting port 44818
• Network traffic containing unusual payload sizes or structures in Ethernet/IP communications
• Multiple device assertion failures occurring in close temporal proximity

Detection Strategies

• Deploy industrial protocol-aware intrusion detection systems (IDS) capable of inspecting CIP traffic
• Monitor for anomalous Ethernet/IP traffic patterns, particularly malformed or oversized CIP messages
• Implement network baseline analysis to identify deviations in communication patterns with 1756-EN4* modules
• Configure SIEM rules to correlate device fault events with network traffic anomalies

Monitoring Recommendations

• Enable logging on network devices and firewalls monitoring traffic to/from 1756-EN4* modules
• Implement continuous asset inventory monitoring to track firmware versions across affected devices
• Configure alerts for unexpected device state changes or communication failures in the industrial network
• Establish baseline metrics for normal CIP communication patterns to identify potential exploitation attempts

How to Mitigate CVE-2023-3596

Immediate Actions Required

• Apply firmware updates from Rockwell Automation as outlined in their security advisory
• Segment industrial networks to limit exposure of 1756-EN4* modules to untrusted networks
• Implement firewall rules to restrict access to Ethernet/IP ports (TCP/UDP 44818) from authorized systems only
• Review and restrict network access to affected devices following principle of least privilege

Patch Information

Rockwell Automation has released security guidance and firmware updates to address this vulnerability. Organizations should consult the Rockwell Automation Security Advisory for specific patch information and update instructions. It is recommended to work with Rockwell Automation support to obtain and deploy the appropriate firmware versions for affected 1756-EN4TR, 1756-EN4TRK, and 1756-EN4TRXT modules.

Workarounds

• Implement network segmentation to isolate affected devices from untrusted networks
• Deploy industrial firewalls or access control lists to restrict CIP traffic to authorized sources only
• Enable application-layer filtering on network security devices to inspect and block malformed CIP messages
• Consider implementing a demilitarized zone (DMZ) architecture for industrial networks

# Example firewall rule to restrict Ethernet/IP access (adapt to your firewall platform)
# Allow CIP traffic only from authorized engineering workstations
iptables -A INPUT -p tcp --dport 44818 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p udp --dport 44818 -s 192.168.100.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 44818 -j DROP
iptables -A INPUT -p udp --dport 44818 -j DROP