CVE-2024-40427

Executive Summary

CVE-2024-40427 is a critical stack buffer overflow vulnerability identified in PX4-Autopilot version 1.14.3. This flaw allows an attacker to execute arbitrary commands by overflowing a stack buffer, leading to a denial of service (DoS) or potential code execution. The vulnerability resides in the autopilot firmware, which is widely used in unmanned aerial vehicles (UAVs) and drones. Given the nature of the affected system, exploitation could result in loss of control over the drone, data exfiltration, or physical damage. No public proof-of-concept (PoC) or patch is currently available, but the risk is elevated due to the potential for remote exploitation in networked environments.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a full assessment. However, based on the vulnerability type (stack buffer overflow) and the context (embedded autopilot system), the following estimated breakdown is provided:

• Attack Vector (AV): Network (AV:N) – likely exploitable over MAVLink or other network protocols.
• Attack Complexity (AC): Low (AC:L) – standard buffer overflow techniques apply.
• Privileges Required (PR): None (PR:N) – no authentication needed.
• User Interaction (UI): None (UI:N) – no user action required.
• Scope (S): Unchanged (S:U) – vulnerability affects the same component.
• Confidentiality (C): High (C:H) – potential for data leakage.
• Integrity (I): High (I:H) – arbitrary code execution possible.
• Availability (A): High (A:H) – DoS is immediate.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Estimated Score: 9.8 (Critical)

Threat Level: Critical – due to the potential for remote code execution on safety-critical drone systems.

Deep Dive & Mechanics

The vulnerability is a classic stack buffer overflow in the PX4-Autopilot firmware, specifically in version 1.14.3. The exact vulnerable function is not publicly documented, but stack overflows in embedded systems often occur in input parsing routines (e.g., MAVLink message handling, parameter updates, or command processing). When a buffer on the stack is written with data exceeding its allocated size, adjacent stack memory (including the return address) can be overwritten. An attacker can craft a malicious payload that overwrites the return address to redirect execution to attacker-controlled shellcode, leading to arbitrary command execution.

In the context of PX4, this could be triggered via:

• MAVLink messages: Sending oversized or malformed messages to the autopilot.
• Parameter updates: Exploiting parameter set commands with long values.
• File system operations: If the vulnerability is in file parsing (e.g., mission files).

The impact is severe: an attacker could take full control of the drone, disable safety features, or cause a crash.

Vulnerable vs. Patched Code

Since no patch is available, a generic comparison is provided:

Vulnerable Code (hypothetical example):

void process_command(char *input) {
    char buffer[64];
    strcpy(buffer, input); // No bounds checking
    // ... process buffer
}

Patched Code (recommended fix):

void process_command(char *input) {
    char buffer[64];
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
    // ... process buffer
}

The patched version uses strncpy with a size limit and ensures null-termination, preventing buffer overflow. The official patch from PX4 is awaited.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• PX4-Autopilot v1.14.3 running on a Pixhawk or similar hardware.
• Network access to the drone’s MAVLink port (default: UDP 14550).
• A tool like mavsdk or pymavlink to send custom MAVLink messages.

Exploitation Steps:

1. Identify the vulnerable endpoint: Use fuzzing tools (e.g., boofuzz) to find the specific MAVLink message that triggers the overflow.
2. Craft the payload: Create a buffer overflow payload that overwrites the return address with a pointer to shellcode. Example shellcode could disable safety checks or execute a system command.
3. Send the payload: Use a script to send the malicious MAVLink message to the drone.

Example Python script (conceptual):

import socket
import struct

# Craft payload (simplified)
payload = b"A" * 64  # Fill buffer
payload += struct.pack("<I", 0x08048400)  # Overwrite return address
payload += b"\x90" * 16  # NOP sled
payload += shellcode  # Attacker's shellcode

# Send via UDP
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(payload, ("192.168.1.100", 14550))

Note: No public exploit code is available; this is a conceptual example.

Blue Team (Defense)

Detection:

• Monitor MAVLink traffic for unusually long messages or malformed packets.
• Use intrusion detection systems (IDS) like Snort or Suricata with custom rules.
• Enable stack canaries in the firmware (if supported) to detect overflow.

Mitigation:

• Isolate the drone network from untrusted sources.
• Use a firewall to restrict MAVLink access to known IPs.
• Apply input validation and bounds checking in custom firmware builds.

Indicators of Compromise (IOCs)

• Network IOCs:
  • MAVLink packets with payload sizes exceeding 256 bytes (normal max is ~255 bytes).
  • Repeated connection attempts from unknown IPs to UDP port 14550.
  • Anomalous MAVLink message IDs (e.g., custom or reserved IDs).
• Host IOCs:
  • Unexpected crashes or reboots of the autopilot.
  • Log entries showing stack corruption or segmentation faults.
  • Unusual system commands executed (e.g., reboot, kill).
• File IOCs:
  • Modified firmware binaries with altered code sections.
  • Presence of shellcode in memory dumps.

Detection Engineering

YARA Rule

rule CVE_2024_40427_StackOverflow {
    meta:
        description = "Detects potential stack overflow payloads targeting PX4-Autopilot v1.14.3"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-40427"
    strings:
        $overflow_pattern = { 41 41 41 41 41 41 41 41 } // 8 'A's as filler
        $mavlink_header = { FE } // MAVLink v1 start byte
    condition:
        $mavlink_header at 0 and #overflow_pattern > 4
}

Sigma Rule

title: CVE-2024-40427 Stack Buffer Overflow in PX4-Autopilot
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects network traffic indicative of exploitation of CVE-2024-40427
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        dest_port: 14550
        payload_length: ">256"
    condition: selection
falsepositives:
    - Legitimate large MAVLink messages (rare)
level: high

Suricata Rule

alert udp any any -> any 14550 (msg:"CVE-2024-40427 PX4 Stack Overflow Attempt"; content:"|FE|"; depth:1; byte_test:1,>,255,1; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems: Disconnect PX4 v1.14.3 drones from untrusted networks.
2. Monitor for IOCs: Use the provided detection rules to identify potential exploitation.
3. Apply workarounds: If possible, restrict MAVLink access via firewall rules (e.g., allow only specific IPs).

Long-term Fix:

• Await an official patch from PX4. Once released, update firmware to the patched version.
• In the interim, consider compiling a custom firmware with stack protection (e.g., -fstack-protector-strong).
• Implement input validation for all MAVLink messages in custom builds.

Vendor Contact: PX4 has not yet released a patch. Monitor their GitHub repository for updates.

Valters IT