Re: OpenBSD local DoS and root exploit

[Jonas Eriksson <je () sekure net>]

The response from the OpenBSD team:
---


Date: Thu, 09 May 2002 08:35:34 -0600
From: Todd C. Miller <Todd.Miller () courtesan com>
To: security-announce () openbsd org
Subject: Potential localhost root hole

In July of 1998 the OpenBSD kernel was modified to populate file
descriptors 0-2 on exec for setuid (and setgid) processes.  This
was done to defeat an attack on setuid programs that open files for
writing and also write to descriptors 0-2 (usually via stdin, stdout
or stderr).

The fix at that time didn't properly deal with the possibility that
the allocation of the dummy descriptors could fail due to a full
file descriptor table.  It has come to our attention that there is
a winnable race condition when the file descriptor table is full,
allowing an fd 0-2 attack to succeed.

Credit for finding this goes to FozZy of Hackademy / Hackerz Voice.
Please see his advisory on bugtraq for more in-depth details.

The following patches are available:

OpenBSD-3.1:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.1/common/003_fdalloc2.patch

OpenBSD-3.0:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.0/common/021_fdalloc2.patch

OpenBSD-2.9:

ftp://ftp.openbsd.org/pub/OpenBSD/patches/2.9/common/026_fdalloc2.patch

OpenBSD-current as well as the OpenBSD 2.9, 3.0 and 3.1 -stable
branches have already been patched.



On Thu, 9 May 2002, Dave Ahmad wrote:

> Hey,
>
> After posting this, Fozzy sent another message mentioning that he left out
> some credit.  I requested that he fix the advisory and re-send it to the
> list, but he hasn't gotten back to me fast enough ;).  This needs to go
> out, so here's the correction:
>
> > I realized this credit problem just after sending my post :
> > "Three weeks ago, XXXXXXXX from Pine released an advisory..." should be :
> > "Three weeks ago, Joost Pol from Pine released an advisory...".
>
> Dave Ahmad
> SecurityFocus
> www.securityfocus.com
>
> On Thu, 9 May 2002 fozzy () dmpfrance com wrote:
>
> > The following is research material from FozZy from Hackademy and Hackerz
> > Voice newspaper (http://www.hackerzvoice.org), and can be distributed
> > modified or not if proper credits are given to them. For educational
> > purposes only, no warranty of any kind, I may be wrong, this post could
> > kill you mail reader, etc.
> >
> >
> > -= OVERVIEW =-
> >
> > On current OpenBSD systems, any local user (being or not in the wheel
> > group) can fill the kernel file descriptors table, leading to a denial of
> > service. Because of a flaw in the way the kernel checks closed file
> > descriptors 0-2 when running a setuid program, it is possible to combine
> > these bugs and earn root access by winning a race condition.


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