CVE-2024-24851

Executive Summary

CVE-2024-24851 is a critical heap-based buffer overflow vulnerability in the Programming Software Connection FiBurn functionality of AutomationDirect P3-550E programmable logic controllers (PLCs) running firmware version 1.2.10.9. The flaw allows an unauthenticated attacker to send a specially crafted network packet, triggering a buffer overflow that can lead to denial of service (DoS) or potentially arbitrary code execution. With a CVSS score of 7.5 (High), this vulnerability poses a significant risk to industrial control systems (ICS) and operational technology (OT) environments. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high due to the critical nature of PLCs in industrial processes.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions are required for exploitation.
• Privileges Required (PR): None – No authentication is needed.
• User Interaction (UI): None – The victim does not need to perform any action.
• Scope (S): Unchanged – The exploit does not affect other components.
• Confidentiality (C): None – No data is exposed.
• Integrity (I): None – No data is modified.
• Availability (A): High – The primary impact is denial of service, potentially crashing the PLC.

Threat Level: High. The vulnerability is remotely exploitable without authentication, making it a prime target for attackers seeking to disrupt industrial processes. The lack of a patch increases the urgency for mitigations.

Deep Dive & Mechanics

The vulnerability resides in the FiBurn functionality of the AutomationDirect P3-550E PLC. FiBurn is a proprietary protocol used for programming and firmware updates over the network. The flaw is a heap-based buffer overflow (CWE-122) that occurs when the PLC processes a specially crafted network packet. The heap overflow can corrupt memory structures, leading to a crash (DoS) or potentially allowing an attacker to overwrite critical data structures for code execution.

Root Cause: The FiBurn handler does not properly validate the size of incoming data before copying it into a heap buffer. An attacker can send a packet with a payload larger than the allocated buffer, causing a write beyond the buffer boundaries.

Attack Vector: An unauthenticated attacker sends a malicious network packet to the PLC’s FiBurn service (typically on a proprietary port). The packet triggers the overflow, corrupting heap metadata or adjacent memory.

Potential Impact:

• Denial of Service: The PLC crashes, halting industrial processes.
• Arbitrary Code Execution: With careful heap manipulation, an attacker could execute arbitrary code, potentially taking full control of the PLC.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code is in the FiBurn packet handler. A hypothetical fix would involve adding bounds checking before memory copy operations.

Vulnerable Code (Conceptual):

void handle_fiburn_packet(char *packet, int size) {
    char *buffer = malloc(256);
    memcpy(buffer, packet, size); // No size check
    // Process buffer...
}

Patched Code (Conceptual):

void handle_fiburn_packet(char *packet, int size) {
    char *buffer = malloc(256);
    if (size > 256) {
        // Reject oversized packet
        free(buffer);
        return;
    }
    memcpy(buffer, packet, size);
    // Process buffer...
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• AutomationDirect P3-550E PLC with firmware 1.2.10.9
• Network access to the PLC’s FiBurn port (default port unknown, likely TCP 502 or a custom port)
• Python with socket library

Exploit Script (Conceptual):

import socket

target_ip = "192.168.1.100"
target_port = 502  # Example port

# Craft a malicious packet with oversized payload
payload = b"A" * 1024  # Overflow buffer
packet = b"\x00\x01" + payload  # Example header + payload

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

Expected Outcome: The PLC crashes or becomes unresponsive, causing a denial of service.

Blue Team (Detection & Defense)

Detection:

• Monitor for unusually large packets on the FiBurn port.
• Use network intrusion detection systems (NIDS) to flag anomalous traffic.
• Enable logging on the PLC and network devices.

Defense:

• Segment the PLC network from corporate IT and the internet.
• Use firewalls to restrict access to the FiBurn port to authorized IPs only.
• Implement network-based anomaly detection.
• Monitor for PLC crashes or unexpected reboots.

Indicators of Compromise (IOCs)

• Network Traffic:
  • Large packets (e.g., >256 bytes) sent to the FiBurn port (TCP 502 or custom port).
  • Repeated connection attempts from unknown IPs.
• System Logs:
  • PLC crash logs or unexpected reboots.
  • Memory corruption errors in PLC diagnostics.
• File Artifacts:
  • No file-based IOCs due to the network-based nature of the exploit.

Detection Engineering

YARA Rule

rule CVE_2024_24851_HeapOverflow {
    meta:
        description = "Detects network packets targeting AutomationDirect P3-550E FiBurn heap overflow"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-24851"
    strings:
        $fiburn_header = { 00 01 } // Example FiBurn header bytes
        $large_payload = /.{256,}/ // Payload > 256 bytes
    condition:
        $fiburn_header and #large_payload > 0
}

Sigma Rule

title: CVE-2024-24851 AutomationDirect P3-550E FiBurn Heap Overflow
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects oversized packets targeting the FiBurn service on AutomationDirect PLCs
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        dest_port: 502
        payload_length: ">256"
    condition: selection
falsepositives:
    - Legitimate firmware updates (rare)
level: high

Suricata Rule

alert tcp any any -> any 502 (msg:"CVE-2024-24851 AutomationDirect P3-550E FiBurn Heap Overflow"; flow:to_server; content:"|00 01|"; depth:2; byte_test:2,>,256,2; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Isolate the PLC network from untrusted networks.
2. Access Control: Restrict access to the FiBurn port to only authorized IPs using firewall rules.
3. Monitoring: Enable logging and monitor for anomalous traffic patterns.
4. Disable Unused Services: If FiBurn is not required, disable the service on the PLC.

Long-Term Actions:

1. Vendor Patch: Monitor AutomationDirect for a firmware update. Apply immediately when available.
2. Upgrade: Consider replacing the P3-550E with a patched or more secure alternative.
3. IDS/IPS: Deploy network intrusion detection/prevention systems with custom rules for this CVE.

Workarounds:

• Use a VPN or dedicated secure channel for PLC programming.
• Implement application-layer filtering to reject oversized packets.

Valters IT