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Category:   Application (Generic)  >   Bzip2 Vendors:   [Multiple Authors/Vendors]
(FreeBSD Issues Fix) bzip2 Race Condition Lets Local Users Modify Permissions of Certain Files
SecurityTracker Alert ID:  1014335
SecurityTracker URL:  http://securitytracker.com/id/1014335
CVE Reference:   CVE-2005-0953   (Links to External Site)
Date:  Jun 29 2005
Impact:   Modification of system information, Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 1.0.2 and prior versions
Description:   A file permission vulnerability was reported in bzip2. A local user can change the permissions of certain files on the target system.

A local user with write access to a directory that the target user is using bzip2 with to extract or compress a file can change the permissions on any file owned by the target user.

When extracting a file, the software applies the permissions of a compressed file to the uncompressed file. However, there is a time period between when the file handle for the uncompressed file is closed and the permissions are changed. A local user can exploit this race condition by replacing the decompressed file with a hardlink to another file on the target system during that time period. The hardlinked file's permissions will be changed to the permissions of the compressed bzip2 file.

Impact:   A local user can cause the permissions on files owned by the target user to be changed when the target user decompresses a file using bzip2.
Solution:   FreeBSD has released a fix and has provided the following instructions [quoted].

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE or 5-STABLE, or to the RELENG_5_4, RELENG_5_3, RELENG_4_11, or RELENG_4_10 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.10, 4.11, 5.3, and 5.4 systems.

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

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:14/bzip2.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:14/bzip2.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/libbz2
# make obj && make depend && make && make install
# cd /usr/src/usr.bin/bzip2
# make obj && make depend && make && make install

Vendor URL:  sources.redhat.com/bzip2/ (Links to External Site)
Cause:   Access control error, State error
Underlying OS:  UNIX (FreeBSD)
Underlying OS Comments:  4.10, 4.11, 5.3, and 5.4

Message History:   This archive entry is a follow-up to the message listed below.
Apr 2 2005 bzip2 Race Condition Lets Local Users Modify Permissions of Certain Files



 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-05:14.bzip2


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

=============================================================================
FreeBSD-SA-05:14.bzip2                                      Security Advisory
                                                          The FreeBSD Project

Topic:          bzip2 denial of service and permission race vulnerabilities

Category:       contrib
Module:         contrib_bzip2
Announced:      2005-06-29
Credits:        Imran Ghory, Chris Evans
Affects:        All FreeBSD releases
Corrected:      2005-06-29 21:38:48 UTC (RELENG_5, 5.4-STABLE)
                2005-06-29 21:41:03 UTC (RELENG_5_4, 5.4-RELEASE-p3)
                2005-06-29 21:42:33 UTC (RELENG_5_3, 5.3-RELEASE-p17)
                2005-06-29 21:43:42 UTC (RELENG_4, 4.11-STABLE)
                2005-06-29 21:45:14 UTC (RELENG_4_11, 4.11-RELEASE-p11)
                2005-06-29 21:46:15 UTC (RELENG_4_10, 4.10-RELEASE-p16)
CVE Name:       CAN-2005-0953, CAN-2005-1260

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

I.   Background

bzip2 is a block-sorting file compression utility.

II.  Problem Description

Two problems have been discovered relating to the extraction of
bzip2-compressed files.  First, a carefully constructed invalid bzip2
archive can cause bzip2 to enter an infinite loop.  Second, when
creating a new file, bzip2 closes the file before setting its
permissions.

III. Impact

The first problem can cause bzip2 to extract a bzip2 archive to an
infinitely large file.  If bzip2 is used in automated processing of
untrusted files this could be exploited by an attacker to create an
denial-of-service situation by exhausting disk space or by consuming
all available cpu time.

The second problem can allow a local attacker to change the
permissions of local files owned by the user executing bzip2 providing
that they have write access to the directory in which the file is
being extracted.

IV.  Workaround

Do not uncompress bzip2 archives from untrusted sources and do not
uncompress files in directories where untrusted users have write
access.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 4-STABLE or 5-STABLE, or to the
RELENG_5_4, RELENG_5_3, RELENG_4_11, or RELENG_4_10 security branch
dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 4.10,
4.11, 5.3, and 5.4 systems.

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

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:14/bzip2.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-05:14/bzip2.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/libbz2
# make obj && make depend && make && make install
# cd /usr/src/usr.bin/bzip2
# 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
  contrib/bzip2/bzip2.c                                       1.1.1.1.2.3
  contrib/bzip2/bzlib.c                                       1.1.1.1.2.3
  contrib/bzip2/compress.c                                    1.1.1.1.2.3
  contrib/bzip2/decompress.c                                  1.1.1.1.2.3
  contrib/bzip2/huffman.c                                     1.1.1.1.2.3
RELENG_4_11
  src/UPDATING                                             1.73.2.91.2.12
  src/sys/conf/newvers.sh                                  1.44.2.39.2.15
  contrib/bzip2/bzip2.c                                  1.1.1.1.2.2.12.1
  contrib/bzip2/bzlib.c                                  1.1.1.1.2.2.12.1
  contrib/bzip2/compress.c                               1.1.1.1.2.2.12.1
  contrib/bzip2/decompress.c                             1.1.1.1.2.2.12.1
  contrib/bzip2/huffman.c                                1.1.1.1.2.2.12.1
RELENG_4_10
  src/UPDATING                                             1.73.2.90.2.17
  src/sys/conf/newvers.sh                                  1.44.2.34.2.18
  contrib/bzip2/bzip2.c                                  1.1.1.1.2.2.10.1
  contrib/bzip2/bzlib.c                                  1.1.1.1.2.2.10.1
  contrib/bzip2/compress.c                               1.1.1.1.2.2.10.1
  contrib/bzip2/decompress.c                             1.1.1.1.2.2.10.1
  contrib/bzip2/huffman.c                                1.1.1.1.2.2.10.1
RELENG_5
  contrib/bzip2/bzip2.c                                       1.1.1.2.8.1
  contrib/bzip2/bzlib.c                                       1.1.1.2.8.1
  contrib/bzip2/compress.c                                    1.1.1.2.8.1
  contrib/bzip2/decompress.c                                  1.1.1.2.8.1
  contrib/bzip2/huffman.c                                     1.1.1.2.8.1
RELENG_5_4
  src/UPDATING                                            1.342.2.24.2.12
  src/sys/conf/newvers.sh                                   1.62.2.18.2.8
  contrib/bzip2/bzip2.c                                      1.1.1.2.12.1
  contrib/bzip2/bzlib.c                                      1.1.1.2.12.1
  contrib/bzip2/compress.c                                   1.1.1.2.12.1
  contrib/bzip2/decompress.c                                 1.1.1.2.12.1
  contrib/bzip2/huffman.c                                    1.1.1.2.12.1
RELENG_5_3
  src/UPDATING                                            1.342.2.13.2.20
  src/sys/conf/newvers.sh                                  1.62.2.15.2.22
  contrib/bzip2/bzip2.c                                      1.1.1.2.10.1
  contrib/bzip2/bzlib.c                                      1.1.1.2.10.1
  contrib/bzip2/compress.c                                   1.1.1.2.10.1
  contrib/bzip2/decompress.c                                 1.1.1.2.10.1
  contrib/bzip2/huffman.c                                    1.1.1.2.10.1
- -------------------------------------------------------------------------

VII. References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-0953
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2005-1260
http://marc.theaimsgroup.com/?l=bugtraq&m=111229375217633
http://scary.beasts.org/security/CESA-2005-002.txt

The latest revision of this advisory is available at
ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:14.bzip.asc
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