Date: Fri, 17 May 1996 16:30:52 -0700 From: FreeBSD Security Officer <security-officer@freebsd.org> To: freebsd-security-notifications@freebsd.org, freebsd-announce@freebsd.org Cc: freebsd-security@freebsd.org Subject: FreeBSD Security Advisory: FreeBSD-SA-96:09.vfsload Message-ID: <199605180006.RAA03132@freefall.freebsd.org>
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=============================================================================
FreeBSD-SA-96:09 Security Advisory
The FreeBSD Project, Inc.
Topic: unauthorized access via mount_union / mount_msdos (vfsload)
Category: core
Module: libc
Announced: 1996-05-17
Affects: FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected: 1996-05-17 2.1-stable and 2.2-current sources
Source: FreeBSD native bug
FreeBSD only: yes
Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:09/
=============================================================================
I. Background
A bug was found in the vfsload(3) library call that affects all
versions of FreeBSD from 2.0 through 2.2-CURRENT that caused a
system vulnerability. This problem is present in all source
code and binary distributions of FreeBSD version 2.x released
before 1996-05-18.
The FreeBSD project is aware of active exploits of this
vulnerability.
All FreeBSD users are encouraged to use the workaround provided
until they can update their operating system to a version with
this vulnerability fixed.
II. Problem Description
The mount_union and mount_msdos programs invoke another system
utility in an insecure fashion while setuid root.
III. Impact
The problem could allow local users to gain unauthorized
permissions.
This vulnerability can only be exploited by users with a valid
account on the local system.
IV. Solution(s)
Update operating system sources and binaries to FreeBSD 2.1-stable
or FreeBSD 2.2-current as distributed later than 1996-05-18 or
if you are currently running 2.1 or later, you may apply the
solution patches available at the URL listed at the top of this
message.
The OS updates fix the actual problem in the vfsload(3) library
routine. Once the vfsload() library routine is fixed, the
workaround listed below is not necessary to solve this problem.
However, an additional stability problem has come to light
(ref. FreeBSD SA-96:10) so the FreeBSD project suggests
using both the setuid workaround and the solution for best results.
V. Workaround
This vulnerability can quickly and easily be limited by removing
the setuid permission bit from the mount_union and mount_msdos
program. This workaround will work for all versions of FreeBSD
affected by this problem.
As root, execute the command:
% chmod u-s /sbin/mount_union /sbin/mount_msdos
then verify that the setuid permissions of the files have been
removed. The permissions array should read "-r-xr-xr-x" as
shown here:
% ls -l /sbin/mount_union /sbin/mount_msdos
-r-xr-xr-x 1 root bin 151552 Apr 26 04:41 /sbin/mount_msdos
-r-xr-xr-x 1 root bin 53248 Apr 26 04:40 /sbin/mount_union
In addition to changing the permissions on the executable files,
if you have the source code installed, we suggest patching the
sources so that mount_union will not be installed with the
setuid bit set:
*** /usr/src/sbin/mount_union/Makefile Sun Nov 20 14:47:52 1994
- --- /usr/src/sbin/mount_union/Makefile Fri May 17 10:36:09 1996
***************
*** 8,14 ****
CFLAGS+= -I${.CURDIR}/../../sys -I${MOUNT}
.PATH: ${MOUNT}
- - BINOWN= root
- - BINMODE=4555
- -
.include <bsd.prog.mk>
- --- 8,11 ----
*** /usr/src/sbin/i386/mount_msdos/Makefile Sun Dec 4 00:01:24 1994
- --- /usr/src/sbin/i386/mount_msdos/Makefile Fri May 17 11:31:57 1996
***************
*** 6,14 ****
SRCS= mount_msdos.c getmntopts.c
MAN8= mount_msdos.8
- - BINOWN= root
- - BINMODE= 4555
- -
MOUNT= ${.CURDIR}/../../mount
CFLAGS+= -I${MOUNT}
.PATH: ${MOUNT}
- --- 6,11 ----
=============================================================================
The FreeBSD Project, Inc.
Web Site: http://www.freebsd.com/
Confidential contacts: security-officer@freebsd.org
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: security-notifications@freebsd.org
Security public discussion: security@freebsd.org
Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=============================================================================
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