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SubjectRe: When to submit something? and: signed executables.
On Mon, Aug 21, 2000 at 11:39:59AM -0600, Charles Cazabon wrote:

Hello Charles,

I submit this to the list since I think it's something that might be of
interest for others.

> Just out of curiosity, what happens if...

> 1. Hacker gets in through sendmail whole or such and gets a root shell.
> 2. Hacker pokes through /proc/kcore and changes the md5sums stored.
> 3. Now no one (including root?) can run any setuid programs, or possibly
> any binaries at all, until the system is restarted or they undo the damage
> in /proc/kcore.

The hacker, obviously being root, could also write a module that tries to
disable the whole MD5 checking thing. He could also mess up everything by
dumping crap to /proc/kcore, without the MD5 thingie.

He could also remove the insmod for the module from the startup scripts,
provocate a reboot...

If one's already root, the system is overtaken. There's always a way if you
are root.

I even would say that if a hacker got root privileges, there's no more need
to replace any binaries. (except for building "entry insurances")

But if he has no complete root shell, and there is a way to somehow
change a binary, put in a trojan horse (how many times a day is an
administrator typing "ls" as root?)... well, that's bad. And the signed exec
module (it's called "signed exec" since I later plan to implement some
public/private key mechanism) prevents this.

It does not prevent an idiot system administrator from doing idiot things
which break security, but maybe it has some advantages.

I believe that security is mostly a conceptual thing, built up by a good
admin with a good network structure. But if we can make a operating system
a little bit more secure, make hacking just a little bit more harder -
why shouldn't we do so?

Just my 2 cents,
Julien

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