bugtraq - Re: Unprivilegued settings for FreeBSD kernel variables

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Message-ID: <20040618180149.GB13459@christian.fuerth.chrullrich.de>
Date: Fri, 18 Jun 2004 20:01:49 +0200
From: Christian Ullrich <chris@...ullrich.de>
To: bugtraq@...urityfocus.com
Subject: Re: Unprivilegued settings for FreeBSD kernel variables


* Eygene A. Ryabinkin wrote on Thursday, 2004-06-17:

> On Tue, Jun 15, 2004 at 09:01:13PM +0200, Dag-Erling SmÃžrgrav wrote:

> > I've already told you that there is no such threat, since the attack
> > you describe can only be initiated by someone who already has
> > unrestricted access.  Please stop wasting everybody's time.

>  You are wrong. Unrestricted access means _really unrestricted_ and
> kernel securelevel restricts access to certain places even to root.

Quite correct.

> IMHO, it's dagerous bug, because some administrators can think "...hmm,
> I've enabled the hardest securelevel and even if a hacker would break
> into my host with r00t privileges he will be restricted in certain ways.

Correct as well.

> But this bug changes things. One can lower securelevel, do some nasty 
> things and raise it again _without reboots_. So, as I've already 
> noted, you are wrong.

No. You CAN'T load or unload kernel modules if securelevel is > 0.

To make your attack work, the attacker would have to have access to
the system before it ever went to securelevel 1, 2 or 3, in order to
load the very kernel module your attack requires. Since that almost
certainly means that he had to be in the same room with the system,
I think "can only be initiated by someone who already has unrestricted
access" is completely correct.

-- 
Christian Ullrich

"There's nothing we can't face -- except for Bun-bun..."