Yeap , getting admin access to any OS where you can mount the root filesystem is super easy ! This is true for Linux and windows and any other OS , too . You can make that task significantly harder by using disk encryption prevents access to the root filesystem , passwords enforced by the BIOSUEFI to prevent booting from other devices preventing users from starting rescue media and using secure boot with custom keys again making it harder to use rescue media and to manipulate the initrdkernel to get around the disk encryption . The combination of these things makes the task of getting root access pretty hardWhen you include the attacker being able to remove the drive and plug it into another machine , then nothing but disk encryption will make the task harder .