GID Games Exploits

[Jimmy Scott]

On Sun, Oct 16, 2005 at 05:04:45AM -0400, Kris Kennaway wrote:
> 
> 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.
> 

I agree this is not a good practice at all, but it is a lot used in
environments where there are clients with no ACL support yet. Or you
don't want the extra ACL support for one directory (and are aware of
these risks, but people aren't; which is explained later).

My point of view is "you don't have ACL's available", which is still the
default as I remember.

> 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.
> 

Your solution is correct, but it is not documented in the handbook or
the security(7) manpage as I can remember, correct me if I'm wrong.

> Kris

-- 
People usually get what's coming to them ... unless it's been mailed.
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