1. Shell Injection: The script uses the os.system() and subprocess methods with string formatting to execute shell commands. This makes the script vulnerable to shell injection attacks, especially if user-supplied input is used. For instance, if an attacker can influence the default_conf or domain_name values, they could potentially execute arbitrary commands.
2. Sensitive Data Exposure: The script prints out the script_user, which could potentially reveal sensitive information about the system. Furthermore, it is handling environment variables that likely contain sensitive information.
3. Arbitrary File Deletion: The script deletes files using the rm -rf command, which is a dangerous operation that can delete directories and their contents recursively. In this case, the default_conf file is deleted. If an attacker can control the path, this could lead to deletion of any file or directory.
4. Insecure File Permissions: The script modifies the file permissions of certain files using the chmod command. This could potentially lead to inappropriate access to sensitive files.
5. Unchecked Return Values: The script does not check the return values of the system or subprocess calls, which can lead to unnoticed failures. If these calls fail, the script continues to execute, which can lead to unexpected behavior.
6. Insecure Temporary File: The script writes the nginx_config to a file, but it does not check if the file already exists. An attacker could potentially create a symlink to another file, and the script would overwrite that file instead.

To mitigate these issues, you should:

• Avoid using os.system() and subprocess with string formatting. Instead, use subprocess.run() with a list of arguments.
• Check the return values of system or subprocess calls and handle errors appropriately.