Patched code sample

import subprocess
import os
import sys

# This code provides a conceptual demonstration of how a vulnerability class
# like the one described in the hypothetical CVE-2025-34193 could be fixed
# in a Python application component.
#
# The original vulnerability stems from multiple factors, including:
# 1. Lack of modern compile-time mitigations (ASLR, DEP, etc.).
# 2. Use of outdated runtimes (Python 2).
# 3. Unsafe handling of external inputs, leading to potential code execution.
#
# While compile-time mitigations must be addressed in the build process and
# runtime updates require migrating the codebase (e.g., from Python 2 to 3),
# the unsafe handling of inputs can be fixed in the code itself.
#
# This example focuses on fixing a command injection vulnerability that could
# arise from processing a maliciously crafted printer driver configuration.

# --- VULNERABLE APPROACH (FOR CONTEXT) ---
#
# In a vulnerable implementation, an external input (like a driver path)
# might be concatenated directly into a command string and executed via a shell.
#
# def vulnerable_install_driver(driver_path):
#     # This is DANGEROUS. If driver_path is "C:\drivers\a.inf && evil.exe",
#     # the shell will execute both commands.
#     command = f"installer.exe /install {driver_path}"
#     os.system(command) # os.system uses a shell, enabling injection.
#
# --- FIXED APPROACH ---

# Define a secure, expected base directory for all printer drivers.
# This prevents path traversal attacks (e.g., using "../..").
ALLOWED_DRIVER_DIRECTORY = "C:\\ProgramData\\Vasion\\Drivers"

def install_printer_driver_safely(driver_config: dict):
    """
    Safely installs a printer driver by validating the input path and executing
    the installer process without a shell.

    This function represents the "fixed" code. It mitigates the risk of
    remote/local code execution from crafted inputs by:
    1.  Validating that the input path is within an expected, safe directory.
    2.  Executing the installer process using a list of arguments, which avoids
        shell interpretation and prevents command injection.
    3.  Using the modern `subprocess` module instead of `os.system`.
    """
    print(f"Attempting to install driver from config: {driver_config}")

    try:
        # 1. Input Sanitization and Validation
        driver_path = driver_config.get("driver_path")
        if not driver_path or not isinstance(driver_path, str):
            raise ValueError("Invalid or missing 'driver_path' in configuration.")

        # Normalize the path to resolve ".." and "." components.
        normalized_path = os.path.normpath(driver_path)

        # Create absolute paths for comparison to prevent bypasses.
        base_path_abs = os.path.abspath(ALLOWED_DRIVER_DIRECTORY)
        driver_path_abs = os.path.abspath(os.path.join(base_path_abs, normalized_path))

        # Security Check: Ensure the final path is within the allowed directory.
        if os.path.commonpath([base_path_abs, driver_path_abs]) != base_path_abs:
            raise SecurityWarning(
                f"Path Traversal Attempt Blocked: '{driver_path}' resolves outside "
                f"the allowed directory '{ALLOWED_DRIVER_DIRECTORY}'."
            )
        
        # Security Check: Ensure the target file actually exists before calling it.
        if not os.path.exists(driver_path_abs):
            raise FileNotFoundError(f"Driver file not found at '{driver_path_abs}'")

        print(f"Validated driver path: {driver_path_abs}")

        # 2. Safe Process Execution
        # The command and its arguments are passed as a list.
        # This ensures that `driver_path_abs` is treated as a single, literal
        # argument and is NOT interpreted by a shell.
        command_args = [
            # Using a placeholder for the actual installer executable
            "C:\\Program Files\\Vasion\\Client\\PrinterInstallerClient.exe",
            "/install",
            driver_path_abs
        ]

        print(f"Executing command: {command_args}")

        # `shell=False` is the default and is critical for security.
        # `check=True` will raise an exception if the command returns a non-zero exit code.
        # We capture output to prevent it from cluttering the main program's stdout/stderr
        # unless needed for debugging.
        result = subprocess.run(
            command_args,
            check=True,
            capture_output=True,
            text=True,
            shell=False # Explicitly ensuring no shell is used.
        )

        print("Driver installation command executed successfully.")
        print(f"Installer STDOUT: {result.stdout.strip()}")

    except ValueError as e:
        print(f"[ERROR] Configuration Error: {e}", file=sys.stderr)
    except (SecurityWarning, FileNotFoundError) as e:
        print(f"[CRITICAL] Security Violation or File Error: {e}", file=sys.stderr)
    except subprocess.CalledProcessError as e:
        print(f"[ERROR] Installer process failed with exit code {e.returncode}", file=sys.stderr)
        print(f"Installer STDERR: {e.stderr.strip()}", file=sys.stderr)
    except Exception as e:
        print(f"[FATAL] An unexpected error occurred: {e}", file=sys.stderr)


if __name__ == '__main__':
    # --- Demonstration ---

    # Ensure the fake allowed directory and a legitimate driver file exist for the demo
    if not os.path.exists(ALLOWED_DRIVER_DIRECTORY):
        os.makedirs(ALLOWED_DRIVER_DIRECTORY)
    
    legit_driver_file = os.path.join(ALLOWED_DRIVER_DIRECTORY, "safe_driver.inf")
    with open(legit_driver_file, "w") as f:
        f.write("# This is a legitimate driver file.")

    # Example 1: A legitimate, safe driver configuration.
    # This should be processed successfully.
    print("--- Running Scenario 1: Legitimate Driver ---")
    safe_config = {
        "driver_name": "Corporate-Printer-v3",
        "driver_path": "safe_driver.inf"
    }
    install_printer_driver_safely(safe_config)
    print("-" * 50)

    # Example 2: A malicious configuration attempting command injection.
    # The vulnerable code would execute `evil.exe`. The fixed code will treat
    # the entire string as a filename, which will fail the `os.path.exists` check.
    print("\n--- Running Scenario 2: Command Injection Attempt ---")
    malicious_injection_config = {
        "driver_name": "malicious",
        "driver_path": 'safe_driver.inf" && "C:\\Windows\\System32\\calc.exe'
    }
    install_printer_driver_safely(malicious_injection_config)
    print("-" * 50)

    # Example 3: A malicious configuration attempting path traversal.
    # The fixed code will detect that the path resolves outside the allowed
    # directory and block the attempt.
    print("\n--- Running Scenario 3: Path Traversal Attempt ---")
    malicious_traversal_config = {
        "driver_name": "traversal",
        "driver_path": "..\\..\\..\\Windows\\System32\\kernel32.dll"
    }
    install_printer_driver_safely(malicious_traversal_config)
    print("-" * 50)

    # Clean up the created dummy file and directory
    os.remove(legit_driver_file)
    os.rmdir(ALLOWED_DRIVER_DIRECTORY)