Setuid Software

Under the Unix operating system there is a notion of privileges, each user who has an account upon a given machine has a specific set of rights.

Often those rights are carefully granted to be minimal, so that ordinary users cannot alter the operating system commands for example.

In some cases these privileges are insufficient to do useful things, for example if the user had the ability to write to the /etc/passwd file they could alter or remove all users passwords - but without access to it they cannot change their own password!

This lead to the notion of commands that give users different privileges whilst they are executed.

A so-called setuid piece of software changes the effective user ID whilst it is being run, typically software is setuid(root) allowing the command to be run by a normal user as if it was being invoked by the superuser, root.

/usr/bin/passwd is traditionally a setuid binary, it runs as the root user so that it may update the system wide password file regardless of who invokes it.

Similarly setgid affects the effective group identity of the user who invokes it. For the duration of the command the user is treated as if they are a member of the given group.

About the lists

One of the first things I did when I set about auditing the Debian GNU/Linux distribution for security flaws was examine the distribution for the setuid/setgid binaries it contained.

This turned out to be a wise move, as many of the binaries which ran with increased privileges turned out to be susceptible to buffer overflows and security attacks.

(The alternative approach of examining services available over a network was also suggested and is a good aproach).

Over time I came to realise that having a single resource containing lists of all the setuid/setgid binaries was a useful thing in its own right.

So these lists were created, as there may be gaps your contributions are welcome.