Re: OpenBSD local DoS and root exploit
From: Jonas Eriksson (je@sekure.net)Date: 05/09/02
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- In reply to: Dave Ahmad: "Re: OpenBSD local DoS and root exploit"
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Date: Thu, 9 May 2002 18:54:31 +0200 (CEST) From: Jonas Eriksson <je@sekure.net> To: bugtraq@securityfocus.com
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. > > > > > >
-- Favourite pickup line: Hey baby, wanna synchronize sequence numbers? Warning: not always effective
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