GID Games Exploits

[Kris Kennaway]

On Sun, Oct 16, 2005 at 10:53:19AM +0200, Jimmy Scott wrote:
> On Sun, Oct 16, 2005 at 10:15:23AM +0200, Mathieu Arnold wrote:
> > 
> > +-le 16/10/2005 00:47 -0400, Kris Kennaway ?crivait :
> > | On Sat, Oct 15, 2005 at 09:39:27PM -0700, Stephen Major wrote:
> > |> It has come to my attention that there are quite a few local exploits
> > |> circling around in the private sector for GID Games.
> > |> 
> > |>  
> > |> 
> > |> Several of the games have vanilla stack overflows in them which can lead to
> > |> elevation of privileges if successfully exploited.
> > | 
> > | Big deal..that's why they're setgid games (which can only write to
> > | game data files) and not setuid anything important :-)
> > 
> > It means that I can change my own score to something better, that's very
> > important :-)
> 
> No ! It means you could access directory trees where your own group
> would not have access to, for example on freeshell.org:
> 
> [sdf] ~> ls -al /usr/pkg/bin/perl                                                
> -rwx---r-x  2 root  users  22246 Aug  7 11:16 /usr/pkg/bin/perl
> 
> Groups are frequently used for negative permissions, because ACL's would
> be overkill or not possible on the filesystem in question.

It's not overkill when the alternative is a security model that is too
fragile or limited to handle your needs.  Unprivileged users/groups
like 'nobody' and 'games' are supposed to be unprivileged, not have
extra privileges that normal users don't get, which is the case in the
above misuse of groups.

The solution is not to give those entities extra privileges: either
use ACLs, or don't install games since they violate your intended
security policy.

Kris
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