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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD Parameter Validation Flaw in nfsclient Lets Local Users Gain Elevated Privileges
SecurityTracker Alert ID:  1024039
SecurityTracker URL:  http://securitytracker.com/id/1024039
CVE Reference:   CVE-2010-2020   (Links to External Site)
Date:  May 27 2010
Impact:   Execution of arbitrary code via local system, Root access via local system
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 7.2, 7.3, 8.0, 8.1
Description:   A vulnerability was reported in the FreeBSD nfsclient. A local user can obtain elevated privileges on the target system.

A local user with privileges to mount filesystems can provide a specially crafted parameter to execute arbitrary code on the target system with kernel level privileges.

Patroklos Argyroudis reported this vulnerability.

Impact:   A local user can execute arbitrary code with kernel level privileges.
Solution:   The vendor has issued a fix and has provided the following solution instructions [quoted].

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the
RELENG_8_0, RELENG_7_3, or RELENG_7_2 security branch dated after the
correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.2, 7.3
and 8.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-10:06/nfsclient.patch
# fetch http://security.FreeBSD.org/patches/SA-10:06/nfsclient.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your vulnerable system via a binary patch:

Systems running 7.2-RELEASE, 7.3-RELEASE, or 8.0-RELEASE on the i386 or
amd64 platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

The vendor's advisory is available at:

http://security.FreeBSD.org/advisories/FreeBSD-SA-10:06.nfsclient.asc

Vendor URL:  security.FreeBSD.org/advisories/FreeBSD-SA-10:06.nfsclient.asc (Links to External Site)
Cause:   Input validation error
Underlying OS:  

Message History:   None.


 Source Message Contents

Date:  Thu, 27 May 2010 03:25:11 GMT
Subject:  FreeBSD Security Advisory FreeBSD-SA-10:06.nfsclient

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

=============================================================================
FreeBSD-SA-10:06.nfsclient                                  Security Advisory
                                                          The FreeBSD Project

Topic:          Unvalidated input in nfsclient

Category:       core
Module:         nfsclient
Announced:      2010-05-27
Credits:        Patroklos Argyroudis
Affects:        FreeBSD 7.2 and later.
Corrected:      2010-05-27 03:15:04 UTC (RELENG_8, 8.1-PRERELEASE)
                2010-05-27 03:15:04 UTC (RELENG_8_0, 8.0-RELEASE-p3)
                2010-05-27 03:15:04 UTC (RELENG_7, 7.3-STABLE)
                2010-05-27 03:15:04 UTC (RELENG_7_3, 7.3-RELEASE-p1)
                2010-05-27 03:15:04 UTC (RELENG_7_2, 7.2-RELEASE-p8)
CVE Name:       CVE-2010-2020

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I.   Background

The Network File System (NFS) allows a host to export some or all of its
file systems so that other hosts can access them over the network and mount
them as if they were on local disks.  FreeBSD includes server and client
implementations of NFS.

II.  Problem Description

The NFS client subsystem fails to correctly validate the length of a
parameter provided by the user when a filesystem is mounted.

III. Impact

A user who can mount filesystems can execute arbitrary code in the kernel.
On systems where the non-default vfs.usermount feature has been enabled,
unprivileged users may be able to gain superuser ("root") privileges.

IV.  Workaround

Do not allow untrusted users to mount filesystems.  To prevent unprivileged
users from mounting filesystems, set the vfs.usermount sysctl variable to
zero:

# sysctl vfs.usermount=0

Note that the default value of this variable is zero, i.e., FreeBSD is not
affected by this vulnerability in its default configuration, and FreeBSD
system administrators are strongly encouraged not to change this setting.

V.   Solution

NOTE WELL: Even with this fix allowing users to mount arbitrary media
should not be considered safe.  Most of the file systems in FreeBSD were
not built to protect safeguard against malicious devices.  While such bugs
in file systems are fixed when found, a complete audit has not been
perfomed on the file system code.

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to the
RELENG_8_0, RELENG_7_3, or RELENG_7_2 security branch dated after the
correction date.

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to FreeBSD 7.2, 7.3
and 8.0 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-10:06/nfsclient.patch
# fetch http://security.FreeBSD.org/patches/SA-10:06/nfsclient.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your vulnerable system via a binary patch:

Systems running 7.2-RELEASE, 7.3-RELEASE, or 8.0-RELEASE on the i386 or
amd64 platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_7
  src/sys/nfsclient/nfs_vfsops.c                                1.193.2.7
  src/lib/libc/sys/mount.2                                       1.45.2.1
RELENG_7_3
  src/UPDATING                                             1.507.2.34.2.3
  src/sys/conf/newvers.sh                                   1.72.2.16.2.5
  src/sys/nfsclient/nfs_vfsops.c                            1.193.2.5.4.2
  src/lib/libc/sys/mount.2                                      1.45.12.2
RELENG_7_2
  src/UPDATING                                            1.507.2.23.2.11
  src/sys/conf/newvers.sh                                  1.72.2.11.2.12
  src/sys/nfsclient/nfs_vfsops.c                            1.193.2.5.2.2
  src/lib/libc/sys/mount.2                                       1.45.8.2
RELENG_8
  src/sys/nfsclient/nfs_vfsops.c                                1.226.2.7
  src/lib/libc/sys/mount.2                                      1.45.10.2
RELENG_8_0
  src/UPDATING                                              1.632.2.7.2.6
  src/sys/conf/newvers.sh                                    1.83.2.6.2.6
  src/sys/nfsclient/nfs_vfsops.c                            1.226.2.2.2.2
  src/lib/libc/sys/mount.2                                  1.45.10.1.2.2
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/6/                                                         r208586
releng/6.4/                                                       r208586
stable/7/                                                         r208586
releng/7.3/                                                       r208586
releng/7.2/                                                       r208586
releng/7.1/                                                       r208586
stable/8/                                                         r208586
releng/8.0/                                                       r208586
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-2020

http://census-labs.com/news/2010/05/26/freebsd-kernel-nfsclient/

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-10:06.nfsclient.asc
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