How a defender shuts each path down

Attack teaches defence

Knowing how each path works tells you exactly how to close it. This is the other half of the skill — the part that keeps real systems safe:

• SUID binaries — audit them (find / -perm -4000) and strip the bit from anything that does not truly need it.
• Sudo rules — grant the narrowest command possible, never a shell or a pager, and avoid NOPASSWD unless essential.
• Writable /etc/passwd — it must be 644, owned by root; the same goes for /etc/shadow (640) and /etc/sudoers.
• Cron scripts — a file run by root must be writable only by root, and live in a directory only root can write.
• PATH in privileged scripts — call programs by full path and set an explicit, trusted PATH; never let a writable dir come first.
• Leaked credentials — keep secrets out of readable files, use a secrets store, and never reuse a password across accounts.

A hardened box is simply one where every item on the enumeration checklist comes back clean.