SUSE Security Announcement: permissions (SUSE-SA:2005:062)
Posted on: 10/24/2005 10:42 AM

A security announcement from SUSE

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Hash: SHA1

______________________________________________________________________________

SUSE Security Announcement

Package: permissions
Announcement ID: SUSE-SA:2005:062
Date: Mon, 24 Oct 2005 08:00:00 +0000
Affected Products: SUSE LINUX 10.0
SUSE LINUX 9.3
SUSE LINUX 9.2
SUSE LINUX 9.1
SuSE Linux 9.0
SuSE Linux Desktop 1.0
SuSE Linux Enterprise Server 8
SUSE SLES 9
UnitedLinux 1.0
Vulnerability Type: information disclosure
Severity (1-10): 4
SUSE Default Package: yes
Cross-References: -

Content of This Advisory:
1) Security Vulnerability Resolved:
information disclosure via permissions package
Problem Description
2) Solution or Work-Around
3) Special Instructions and Notes
4) Package Location and Checksums
5) Pending Vulnerabilities, Solutions, and Work-Arounds:
- See SUSE Security Summary Report
6) Authenticity Verification and Additional Information

______________________________________________________________________________

1) Problem Description and Brief Discussion

SUSE LINUX ships with three pre defined sets of permissions, 'easy',
'secure' and 'paranoid'. The chkstat program contained in the
permissions package is used to set those permissions to the chosen
level. Level 'easy' which is the default allows some world writeable
directories. /usr/src/packages/RPMS and subdirectories is among
them. To prevent users from playing tricks in there e.g. linking to
/etc/shadow chkstat doesn't touch symlinks or files with an hardlink
count != 1.

Stefan Nordhausen discovered a way to trick this check. To gain
access to e.g. /etc/shadow a malicious user has to place a hardlink
to that file at a place that is modified by chkstat. chkstat will
not touch the file because it has a hardlink count of two. However,
if the administrator modifies the user database the original
/etc/shadow gets deleted and replaced by a new one. That means the
hardlink count of the file created by the malicious user drops to
one. At this point chkstat will modify the file's permissions so
anyone can read it. So it's technically impossible for chkstat to
modify permissions of files in world writeable directories in a
secure way.

One such world writeable directoy in level 'easy' is
/usr/src/packages/RPMS. Only subdirectories need to be adjusted in
this case. Since normal users cannot create hard links to
directories the problem can be solved by telling chkstat to not
accept regular files. Another problematic directory is /var/games.
Only members of group 'games' may write to it but it's likely that
games with setgid 'games' are exploitable to allow user to gain
group 'games' membership.

The updated permissions package now tells chkstat when to only
accept directories and no longer touches anything below /var/games
to solve the described problems. On SUSE Linux 9.0 xmcd contained
world writeable directories that suffered from the same problems.
Updated xmcd packages for SUSE Linux 9.0 are therefore provided as
well.

We like to thank Stefan Nordhausen for pointing out the problems.

2) Solution or Work-Around

In permissions level 'secure' no games are setgid 'games' and
/usr/src/packages is not world writeable. You are safe if you
switched to that level before any potentially malicious users could
log in.

3) Special Instructions and Notes

None

4) Package Location and Checksums

The preferred method for installing security updates is to use the YaST
Online Update (YOU) tool. YOU detects which updates are required and
automatically performs the necessary steps to verify and install them.
Alternatively, download the update packages for your distribution manually
and verify their integrity by the methods listed in Section 6 of this
announcement. Then install the packages using the command

rpm -Fhv <file.rpm>

to apply the update, replacing <file.rpm> with the filename of the
downloaded RPM package.


x86 Platform:

SUSE LINUX 10.0:
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/i586/filesystem-10.0-4.2.i586.rpm
5f634cb4cd45ad3283e6055c3794ecff
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/i586/permissions-2005.10.20-0.1.i586.rpm
7e9beef0e8df0ba419ff64ac96ad57e1

SUSE LINUX 9.3:
ftp://ftp.suse.com/pub/suse/i386/update/9.3/rpm/i586/permissions-2005.10.20-0.1.i586.rpm
216afa8469276198015e5fff177580d2

SUSE LINUX 9.2:
ftp://ftp.suse.com/pub/suse/i386/update/9.2/rpm/i586/permissions-2005.10.20-0.1.i586.rpm
3d61d27c7bf81889a321972ac12dcaab

SUSE LINUX 9.1:
ftp://ftp.suse.com/pub/suse/i386/update/9.1/rpm/i586/permissions-2005.10.20-0.2.i586.rpm
72d9a0b5b0b750fb656aa54eb7c6ebdd

SuSE Linux 9.0:
ftp://ftp.suse.com/pub/suse/i386/update/9.0/rpm/i586/permissions-2005.10.20-3.i586.rpm
cf8c022048e93fc6d159913ad7824e6a
ftp://ftp.suse.com/pub/suse/i386/update/9.0/rpm/i586/xmcd-3.0.2-552.i586.rpm
f3e82cf342c45ab46fca16c98587b22d

Power PC Platform:

SUSE LINUX 10.0:
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/ppc/filesystem-10.0-4.2.ppc.rpm
f0077c15af6a95edbd7aa25055668967
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/ppc/permissions-2005.10.20-0.1.ppc.rpm
7f6552f5450b98821912c8703c580b38

x86-64 Platform:

SUSE LINUX 10.0:
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/x86_64/filesystem-10.0-4.2.x86_64.rpm
214b7d7fc6dfdac3e07eff2ad4abf0e9
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/x86_64/permissions-2005.10.20-0.1.x86_64.rpm
7b15cb94762ae6bc1cd7e441a08c39b4

SUSE LINUX 9.3:
ftp://ftp.suse.com/pub/suse/i386/update/9.3/rpm/x86_64/permissions-2005.10.20-0.1.x86_64.rpm
0d11d64965eee2cefeb56edfe258fee4

SUSE LINUX 9.2:
ftp://ftp.suse.com/pub/suse/i386/update/9.2/rpm/x86_64/permissions-2005.10.20-0.1.x86_64.rpm
4f2373ed4a93e3974b919e595a9490b7

SUSE LINUX 9.1:
ftp://ftp.suse.com/pub/suse/x86_64/update/9.1/rpm/x86_64/permissions-2005.10.20-0.2.x86_64.rpm
3ca12f4aae9b7a1b484e6a0e4f8f658d

SuSE Linux 9.0:
ftp://ftp.suse.com/pub/suse/x86_64/update/9.0/rpm/x86_64/permissions-2005.10.20-3.x86_64.rpm
853503b8868c1d2a34d05aaf6824cf83
ftp://ftp.suse.com/pub/suse/x86_64/update/9.0/rpm/x86_64/xmcd-3.0.2-552.x86_64.rpm
fd95ac5dd3980af5308abe7062849149

Sources:

SUSE LINUX 10.0:
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/src/filesystem-10.0-4.2.src.rpm
1784328035be5507b20737a2edfce8d8
ftp://ftp.suse.com/pub/suse/i386/update/10.0/rpm/src/permissions-2005.10.20-0.1.src.rpm
0fc7ffe7a9688f04c916c50709db08da

SUSE LINUX 9.3:
ftp://ftp.suse.com/pub/suse/i386/update/9.3/rpm/src/permissions-2005.10.20-0.1.src.rpm
0a856cadf3b65db9434f20203413aba3

SUSE LINUX 9.2:
ftp://ftp.suse.com/pub/suse/i386/update/9.2/rpm/src/permissions-2005.10.20-0.1.src.rpm
57c3240513c9861634e79547df4f8cf0

SUSE LINUX 9.1:
ftp://ftp.suse.com/pub/suse/i386/update/9.1/rpm/src/permissions-2005.10.20-0.2.src.rpm
b47b5e76f759227d325a33dbbcb5ae96
ftp://ftp.suse.com/pub/suse/x86_64/update/9.1/rpm/src/permissions-2005.10.20-0.2.src.rpm
f98fa35639b7d118e6aed1ecb99c4cbb

SuSE Linux 9.0:
ftp://ftp.suse.com/pub/suse/i386/update/9.0/rpm/src/permissions-2005.10.20-3.src.rpm
8fa2759f6d2012aee4571e5830ea26eb
ftp://ftp.suse.com/pub/suse/i386/update/9.0/rpm/src/xmcd-3.0.2-552.src.rpm
44f64e89f871fd07bd6291d88277b327
ftp://ftp.suse.com/pub/suse/x86_64/update/9.0/rpm/src/permissions-2005.10.20-3.src.rpm
48857a183ff120bc39ebb280eaca8764
ftp://ftp.suse.com/pub/suse/x86_64/update/9.0/rpm/src/xmcd-3.0.2-552.src.rpm
9e961bdfaf2c935857eb86bd64b74c83

Our maintenance customers are notified individually. The packages are
offered for installation from the maintenance web:

http://support.novell.com/cgi-bin/search/searchtid.cgi?psdb/f91efcfdcc1e3f92b382d1725439765d.html
http://portal.suse.com/psdb/f91efcfdcc1e3f92b382d1725439765d.html
http://support.novell.com/cgi-bin/search/searchtid.cgi?psdb/5811be293ad9fa388c6d368261df375d.html
http://portal.suse.com/psdb/5811be293ad9fa388c6d368261df375d.html

______________________________________________________________________________

5) Pending Vulnerabilities, Solutions, and Work-Arounds:

- See SUSE Security Summary Report

______________________________________________________________________________

6) Authenticity Verification and Additional Information

- Announcement authenticity verification:

SUSE security announcements are published via mailing lists and on Web
sites. The authenticity and integrity of a SUSE security announcement is
guaranteed by a cryptographic signature in each announcement. All SUSE
security announcements are published with a valid signature.

To verify the signature of the announcement, save it as text into a file
and run the command

gpg --verify <file>

replacing <file> with the name of the file where you saved the
announcement. The output for a valid signature looks like:

gpg: Signature made <DATE> using RSA key ID 3D25D3D9
gpg: Good signature from "SuSE Security Team <security@suse.de>"

where <DATE> is replaced by the date the document was signed.

If the security team's key is not contained in your key ring, you can
import it from the first installation CD. To import the key, use the
command

gpg --import gpg-pubkey-3d25d3d9-36e12d04.asc

- Package authenticity verification:

SUSE update packages are available on many mirror FTP servers all over the
world. While this service is considered valuable and important to the free
and open source software community, the authenticity and the integrity of
a package needs to be verified to ensure that it has not been tampered
with.

There are two verification methods that can be used independently from
each other to prove the authenticity of a downloaded file or RPM package:

1) Using the internal gpg signatures of the rpm package
2) MD5 checksums as provided in this announcement

1) The internal rpm package signatures provide an easy way to verify the
authenticity of an RPM package. Use the command

rpm -v --checksig <file.rpm>

to verify the signature of the package, replacing <file.rpm> with the
filename of the RPM package downloaded. The package is unmodified if it
contains a valid signature from build@suse.de with the key ID 9C800ACA.

This key is automatically imported into the RPM database (on
RPMv4-based distributions) and the gpg key ring of 'root' during
installation. You can also find it on the first installation CD and at
the end of this announcement.

2) If you need an alternative means of verification, use the md5sum
command to verify the authenticity of the packages. Execute the command

md5sum <filename.rpm>

after you downloaded the file from a SUSE FTP server or its mirrors.
Then compare the resulting md5sum with the one that is listed in the
SUSE security announcement. Because the announcement containing the
checksums is cryptographically signed (by security@suse.de), the
checksums show proof of the authenticity of the package if the
signature of the announcement is valid. Note that the md5 sums
published in the SUSE Security Announcements are valid for the
respective packages only. Newer versions of these packages cannot be
verified.

- SUSE runs two security mailing lists to which any interested party may
subscribe:

suse-security@suse.com
- General Linux and SUSE security discussion.
All SUSE security announcements are sent to this list.
To subscribe, send an e-mail to
<suse-security-subscribe@suse.com>.

suse-security-announce@suse.com
- SUSE's announce-only mailing list.
Only SUSE's security announcements are sent to this list.
To subscribe, send an e-mail to
<suse-security-announce-subscribe@suse.com>.

For general information or the frequently asked questions (FAQ),
send mail to <suse-security-info@suse.com> or
<suse-security-faq@suse.com>.

=====================================================================
SUSE's security contact is <security@suse.com> or <security@suse.de>.
The <security@suse.de> public key is listed below.
=====================================================================
______________________________________________________________________________

The information in this advisory may be distributed or reproduced,
provided that the advisory is not modified in any way. In particular, the
clear text signature should show proof of the authenticity of the text.

SUSE Linux Products GmbH provides no warranties of any kind whatsoever
with respect to the information contained in this security advisory.

Type Bits/KeyID Date User ID
pub 2048R/3D25D3D9 1999-03-06 SuSE Security Team <security@suse.de>
pub 1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <build@suse.de>

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