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UNIRAS Brief - 808/06 - FreeBSD Security Advisory: FreeBSD-SA-06:26.gtar



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______________________________________________________________________________

 UNIRAS (UK Government CERT) Briefing - 808/06 dated 06.12.06 time 14:00
 UNIRAS is part of NISCC (the UK National Infrastructure Security
 Co-ordination Centre)
______________________________________________________________________________

 UNIRAS material is available from the NISCC website at www.niscc.gov.uk
______________________________________________________________________________

Title
=====

FreeBSD Security Advisory: FreeBSD-SA-06:26.gtar                                      

Detail
======

Symlinks created using the "GNUTYPE_NAMES" tar extension can be absolute due 
to lack of proper sanity checks.


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=============================================================================
FreeBSD-SA-06:26.gtar                                      Security Advisory
                                                          The FreeBSD Project

Topic:          gtar name mangling symlink vulnerability

Category:       contrib
Module:         contrib_tar
Announced:      2006-12-06
Credits:        Teemu Salmela
Affects:        FreeBSD 4.x and 5.x releases
Corrected:      2006-12-06 09:16:17 UTC (RELENG_5, 5.5-STABLE)
                2006-12-06 09:16:41 UTC (RELENG_5_5, 5.5-RELEASE-p9)
                2006-12-06 09:17:09 UTC (RELENG_4, 4.11-STABLE)
                2006-12-06 09:18:02 UTC (RELENG_4_11, 4.11-RELEASE-p26)
CVE Name:       CVE-2006-6097

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

GNU tar (gtar) is a utility to create and extract "tape archives", commonly known as tar files.  GNU tar is included in FreeBSD 4.x
as /usr/bin/tar, and in FreeBSD 5.x as /usr/bin/gtar.

II.  Problem Description

Symlinks created using the "GNUTYPE_NAMES" tar extension can be absolute due to lack of proper sanity checks.

III. Impact

If an attacker can get a user to extract a specially crafted tar archive the attacker can overwrite arbitrary files with the
permissions of the user running gtar.  If file system permissions allow it, this may allow the attacker to overwrite important
system file (if gtar is being run as root), or important user configuration files such as .tcshrc or .bashrc, which would allow the
attacker to run arbitrary commands.

IV.  Workaround

Use "bsdtar", which is the default tar implementation in FreeBSD 5.3 and higher.  For FreeBSD 4.x, bsdtar is available in the
FreeBSD Ports Collection as ports/archivers/libarchive.

V.   Solution

NOTE: The solution described below causes GNU tar to exit with an error when handling an archive with GNUTYPE_NAMES entries.  The
FreeBSD Security Team does not consider this to be a significant regression, since GNUTYPE_NAMES has not been used for many years
and is not supported by other archival software such as libarchive(3); but the original (insecure) behaviour can be retained by
running GNU tar with the newly added --allow-name-mangling option.

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE, or 5-STABLE, or to the
RELENG_5_5 or RELENG_4_11 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.11 and
5.5 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-06:26/gtar.patch
# fetch http://security.FreeBSD.org/patches/SA-06:26/gtar.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/gnu/usr.bin/tar
# make obj && make depend && make && make install

VI.  Correction details

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

Branch                                                           Revision
  Path
- - -------------------------------------------------------------------------
RELENG_4
  src/contrib/tar/src/common.h                                    1.2.2.2
  src/contrib/tar/src/extract.c                                   1.4.2.4
  src/contrib/tar/src/tar.c                                       1.2.2.3
RELENG_4_11
  src/UPDATING                                             1.73.2.91.2.27
  src/sys/conf/newvers.sh                                  1.44.2.39.2.30
  src/contrib/tar/src/common.h                               1.2.2.1.10.1
  src/contrib/tar/src/extract.c                               1.4.2.3.8.1
  src/contrib/tar/src/tar.c                                   1.2.2.2.6.1
RELENG_5
  src/contrib/tar/src/common.h                                   1.2.10.1
  src/contrib/tar/src/extract.c                                   1.6.8.1
  src/contrib/tar/src/tar.c                                       1.3.4.1
RELENG_5_5
  src/UPDATING                                             1.342.2.35.2.9
  src/sys/conf/newvers.sh                                  1.62.2.21.2.11
  src/contrib/tar/src/common.h                                   1.2.22.1
  src/contrib/tar/src/extract.c                                  1.6.20.1
  src/contrib/tar/src/tar.c                                      1.3.16.1
- - -------------------------------------------------------------------------

VII. References

http://marc.theaimsgroup.com/?l=full-disclosure&m=116414883029517
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-6097

The latest revision of this advisory is available at http://security.FreeBSD.org/advisories/FreeBSD-SA-06:26.gtar.asc
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______________________________________________________________________________

UNIRAS wishes to acknowledge the contributions of FreeBSD for the
information contained in this briefing.
______________________________________________________________________________

This notice contains information released by the original author.
Some of the information may have changed since it was released. If the
vulnerability affects you, it may be prudent to retrieve the advisory
from the site of the original source to ensure that you receive the most
current information concerning that problem.

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imply its endorsement, recommendation, or favouring by UNIRAS or NISCC.
The views and opinions of authors expressed within this notice shall not
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Neither UNIRAS or NISCC shall also accept responsibility for any errors
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shall not be liable for any loss or damage whatsoever, arising from or
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UNIRAS is a member of the Forum of Incident Response and Security Teams
(FIRST) and has contacts with other international Incident Response
Teams (IRTs) in order to foster cooperation and coordination in incident
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information sharing amongst its members and the community at large.
______________________________________________________________________________

<End of UNIRAS Briefing>

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