Introduction to AAOS Security Auditing

Android Automotive OS (AAOS) is rapidly becoming the standard for in-vehicle infotainment (IVI) systems. Its open-source nature and rich feature set offer immense opportunities for innovation, but also introduce unique security challenges. Unlike traditional Android devices, AAOS is deeply integrated into the vehicle’s critical systems, making its security paramount. Vulnerabilities in AAOS can have severe consequences, ranging from data breaches to vehicle compromise. Therefore, a robust and continuous security auditing process is essential.

Traditional security scanning tools often fall short when dealing with the specific architecture and automotive-centric customizations of AAOS. This article details how to build a custom, script-based security audit tool tailored for AAOS, enabling automated vulnerability scans and compliance checks.

The Need for a Custom Tool

Generic vulnerability scanners, while useful, typically lack the deep understanding of AAOS’s unique attack surfaces and configuration nuances. Key reasons for developing a custom tool include:

• Automotive Specifics: AAOS features like Vehicle HAL, CarService, and specific power management modes require specialized checks.
• Deep System Access: Leveraging adb and low-level shell commands to inspect configurations, permissions, and network states often missed by high-level scanners.
• Custom Compliance: Tailoring checks to automotive industry standards (e.g., ISO 26262, UNECE WP.29 regulations) and OEM-specific security policies.
• Integration with CI/CD: A script-based approach can be easily integrated into continuous integration/continuous deployment pipelines for automated security gates.
• Early Detection: Identifying misconfigurations or vulnerabilities early in the development lifecycle reduces remediation costs and risks.

Designing Your AAOS Security Audit Tool

Our custom tool will primarily be a Python script leveraging the Android Debug Bridge (ADB) to interact with the AAOS device. Python’s versatility, rich library ecosystem, and ease of scripting make it an ideal choice. The tool will be modular, allowing for easy expansion and maintenance.

Setting Up Your Environment

Before writing the script, ensure you have the following prerequisites:

• ADB (Android Debug Bridge): Installed and configured on your host machine.
• Python 3: Installed, along with the subprocess module (usually built-in).
• AAOS Device: A physical or emulated AAOS device with ADB debugging enabled.

Connect your host machine to the AAOS device:

adb devices

You should see your device listed. If not, troubleshoot your ADB connection.

Core Audit Modules and Implementation

Let’s break down the audit into several key areas, demonstrating how to implement checks for each.

1. ADB Service Security

The ADB service, while crucial for development, can be a significant security risk if left exposed. We’ll check its status and configuration.

Python Script Snippet: Check ADB Status

import subprocess

def run_adb_command(command):
    try:
        result = subprocess.run(['adb', 'shell'] + command, capture_output=True, text=True, check=True)
        return result.stdout.strip()
    except subprocess.CalledProcessError as e:
        print(f"Error running ADB command: {e}")
        print(f"Stderr: {e.stderr}")
        return ""

def check_adb_security():
    print("n--- Checking ADB Security ---")
    # Check if ADB over TCP is enabled (common misconfiguration for remote debugging)
    adb_tcp_port = run_adb_command(['getprop', 'service.adb.tcp.port'])
    if adb_tcp_port and adb_tcp_port != "-1":
        print(f"  [CRITICAL] ADB over TCP is enabled on port: {adb_tcp_port}")
        print("    Remediation: Disable by running 'setprop service.adb.tcp.port -1' and reboot.")
    else:
        print("  [OK] ADB over TCP is disabled or not configured.")

    # Check if ADB authentication is enforced (always expected on user builds)
    # This is harder to check directly via shell, but we can look for system properties
    # A more robust check involves trying to connect without a key on a fresh device.
    # For simplicity, we assume 'persist.adb.secure=1' implies enforcement for this example.
    adb_secure = run_adb_command(['getprop', 'persist.adb.secure'])
    if adb_secure == '1':
        print("  [OK] ADB secure mode (authentication) is likely enforced.")
    else:
        print("  [WARNING] ADB secure mode might not be enforced (persist.adb.secure != 1).")

    # Check for unauthorized ADB connections (requires parsing 'adb devices' output on host)
    # This part would typically be run on the host system, not via adb shell.
    # For this script's scope, we focus on device-side config.

2. Application & Package Analysis

Unwanted, debuggable, or excessively permissioned applications can create attack vectors.

Python Script Snippet: Scan Installed Packages

def scan_packages():
    print("n--- Scanning Installed Packages ---")
    packages_raw = run_adb_command(['pm', 'list', 'packages', '-f'])
    packages = [line.split('=')[-1] for line in packages_raw.splitlines() if line.strip()]

    debuggable_apps = []
    system_apps_with_dangerous_perms = []

    for pkg in packages:
        # Check for debuggable flag
        package_info = run_adb_command(['dumpsys', 'package', pkg])
        if "debuggable=true" in package_info:
            debuggable_apps.append(pkg)

        # Check for system apps with dangerous permissions (example: android.permission.CAMERA)
        if "/system/app" in package_info or "/system/priv-app" in package_info:
            # Example check for a specific dangerous permission
            if "android.permission.CAMERA" in package_info and "GRANTED" in package_info.split("android.permission.CAMERA")[1]:
                system_apps_with_dangerous_perms.append(pkg)

    if debuggable_apps:
        print("  [CRITICAL] Debuggable applications found:")
        for app in debuggable_apps:
            print(f"    - {app}")
        print("    Remediation: Ensure debuggable flag is 'false' for production builds.")
    else:
        print("  [OK] No debuggable applications found.")

    if system_apps_with_dangerous_perms:
        print("  [WARNING] System apps with potentially dangerous permissions:")
        for app in system_apps_with_dangerous_perms:
            print(f"    - {app} (e.g., CAMERA)")
        print("    Remediation: Review permissions of system applications.")
    else:
        print("  [OK] No system apps found with example dangerous permissions.")

3. Network Configuration Review

An open network stack or misconfigured firewall rules can expose the AAOS device to external threats.

Python Script Snippet: Network Checks

def check_network_config():
    print("n--- Checking Network Configuration ---")

    # Check open ports
    open_ports = run_adb_command(['netstat', '-tuln'])
    print("  Active network listeners (TCP/UDP):")
    for line in open_ports.splitlines():
        if "LISTEN" in line or "UDP" in line:
            print(f"    {line.strip()}")
    print("    Remediation: Investigate unexpected open ports; restrict access via firewall.")

    # Check iptables rules (basic check for non-empty rulesets)
    iptables_rules = run_adb_command(['iptables', '-L'])
    if "Chain INPUT" in iptables_rules and "Chain FORWARD" in iptables_rules:
        print("  [OK] iptables rules detected. Review for proper ingress/egress filtering.")
        # Further parsing could check for specific rules, e.g., default DROP policy
    else:
        print("  [WARNING] iptables rules not found or output unexpected. System might lack firewall.")

    # Check Wi-Fi configuration if applicable (e.g., open networks, WPA enterprise settings)
    # This often requires more specific commands or access to system logs.
    # Example: run_adb_command(['dumpsys', 'wifi'])
    print("  Review Wi-Fi configuration manually if applicable (e.g., via 'dumpsys wifi').")

4. SELinux Policy Enforcement

SELinux is critical for enforcing Mandatory Access Control (MAC) policies. Misconfigurations can severely weaken the system.

Python Script Snippet: SELinux Status

def check_selinux_status():
    print("n--- Checking SELinux Status ---")

    enforce_status = run_adb_command(['getenforce'])
    if enforce_status == "Enforcing":
        print("  [OK] SELinux is in Enforcing mode.")
    elif enforce_status == "Permissive":
        print("  [CRITICAL] SELinux is in Permissive mode. This significantly weakens security.")
        print("    Remediation: Ensure SELinux is set to Enforcing in production builds.")
    else:
        print(f"  [WARNING] Unknown SELinux status: {enforce_status}")

    policy_version = run_adb_command(['cat', '/sys/fs/selinux/policyvers'])
    if policy_version:
        print(f"  SELinux Policy Version: {policy_version}")
    else:
        print("  [WARNING] Could not retrieve SELinux policy version.")

5. System & Kernel Hardening

Basic kernel hardening measures can significantly reduce the attack surface.

Python Script Snippet: Kernel Checks

def check_kernel_hardening():
    print("n--- Checking Kernel Hardening ---")

    # Check kptr_restrict (hides kernel pointer addresses from unprivileged users)
    kptr_restrict = run_adb_command(['sysctl', 'kernel.kptr_restrict'])
    if "= 1" in kptr_restrict or "= 2" in kptr_restrict:
        print("  [OK] kernel.kptr_restrict is enabled (value 1 or 2).")
    else:
        print("  [WARNING] kernel.kptr_restrict is disabled or misconfigured. Consider enabling.")

    # Check for unknown kernel modules loaded (may indicate compromise or unauthorized components)
    loaded_modules = run_adb_command(['lsmod'])
    print("  Loaded Kernel Modules (review for unauthorized entries):")
    if loaded_modules:
        for line in loaded_modules.splitlines():
            print(f"    {line.strip()}")
    else:
        print("    No kernel modules found (unexpected or device doesn't use them like this).")
    print("    Remediation: Investigate any unfamiliar or unauthorized kernel modules.")

Reporting and Compliance

Once the audit checks are performed, the tool should generate a clear, actionable report. This report can be in various formats:

• Console Output: As shown in the snippets above, providing immediate feedback.
• JSON/XML: For programmatic consumption and integration with other tools.
• HTML: For human-readable, formatted reports with severity levels.
• CSV: For simple data export and spreadsheet analysis.

Each finding should include:

• Severity: Critical, High, Medium, Low, Informational.
• Description: What the vulnerability is.
• Recommendation: How to fix it.
• Compliance Mapping: Which industry standards (e.g., ISO 26262 requirement X, UNECE WP.29 regulation Y) or internal policies the finding relates to.

Integrating this tool into a CI/CD pipeline allows for automated scanning after every build, providing continuous security assurance and helping to maintain compliance throughout the development lifecycle.

Conclusion

Building a custom AAOS security audit tool, leveraging Python and ADB, provides a powerful and flexible solution for addressing the unique security challenges of automotive systems. By automating vulnerability scans and compliance checks, development teams can proactively identify and remediate security weaknesses, ensure adherence to industry standards, and ultimately deliver a more secure and reliable in-vehicle experience. This approach empowers developers and security engineers to maintain a strong security posture in the rapidly evolving landscape of connected vehicles.