Vulnerable code sample

import subprocess

class CodeInterpreterSandbox:
    """
    A simplified representation of a code execution environment that can install packages.
    """
    def install_packages(self, package_names: list):
        """
        VULNERABLE IMPLEMENTATION (Pre-patch)

        Installs Python packages by constructing a shell command from a list of names.
        This method is vulnerable to command injection because it does not sanitize
        the package names before joining them into a command string that is executed
        with `shell=True`.
        """
        if not package_names:
            return

        # VULNERABLE: Package names are directly joined into a string.
        # An attacker can include shell metacharacters (e.g., ';', '&&', '|')
        # in a "package name" to execute arbitrary commands.
        packages_str = " ".join(package_names)
        command = f"pip install {packages_str}"

        # The use of `shell=True` with the unsanitized `command` string
        # allows for command injection.
        try:
            subprocess.run(
                command,
                shell=True,
                check=True,
                capture_output=True,
                text=True
            )
        except subprocess.CalledProcessError as e:
            # In a real scenario, error handling would be more robust.
            print(f"Failed to execute: {e.stderr}")