1. Topic:
lpr has a format string security bug. It also mishandles any extension to
the lpd communication protocol, and assumes that the instructions contained
in the extension are a file it should try to print. It also has a race
condition in the handling of queue interactions that can cause the queue to
wedge.
Note: Packages indicated in revision -03 and earlier were not signed with
the Red Hat GPG key. This has been corrected.
2. Problem description:
The old BSD-based lpr which we shipped with Red Hat Linux 5.x and 6.x has a
recently discovered format string bug in its calls to the syslog facility.
While we are not aware of any exploits for this issue, it might be possible
for a user to gain local root access. For this reason, upgrading to the
new lpr is strongly encouraged.
Additionally, lpr did not properly handle extensions to the lpd protocol.
LPRng, an advanced replacement for lpr included in Red Hat Linux 7, makes
use of extensions. The lpr included in Red Hat Linux 6.2 and earlier will
not recognize these extensions, and attempt to handle the instructions as
if they were a file to be printed. As a result, the lpr system sends out
three of the following email messages per print job:
Date: Thu, 10 Aug 2000 21:36:32 -0400
From: bin <bin@redhat.com>
Reply-To: root@yyyyy.redhat.com
To: xxxx@xxxxxx.redhat.com
Subject: lp printer job "(stdin)"
Your printer job ((stdin))
was not printed because the daemon could not stat the file
Additionaly, a race condition exists in the contention for the lock file,
making it posible for the queue to get into a wedged state.
These problems are now fixed.
3. Bug IDs fixed: (see bugzilla for more information)
16032 - LPRng lpd/BSD lpd generate stat errors in LPRng->BSD queue interactions.
11740 - Race condition in locking for LPD
16725 - BSD lpr 0.50-5 Errata Tracking Bug
4. Relevant releases/architectures:
Red Hat Linux 5.0 - i386, alpha
Red Hat Linux 5.1 - i386, alpha, sparc
Red Hat Linux 5.2 - i386, alpha, sparc
Red Hat Linux 6.0 - i386, alpha, sparc
Red Hat Linux 6.1 - i386, alpha, sparc
Red Hat Linux 6.2 - i386, alpha, sparc
5. RPMs required:
Red Hat Linux 5.2:
alpha:
ftp://updates.redhat.com/5.2/en/os/alpha/lpr-0.50-7.5.x.alpha.rpm
sparc:
ftp://updates.redhat.com/5.2/en/os/sparc/lpr-0.50-7.5.x.sparc.rpm
i386:
ftp://updates.redhat.com/5.2/en/os/i386/lpr-0.50-7.5.x.i386.rpm
sources:
ftp://updates.redhat.com/5.2/en/os/SRPMS/lpr-0.50-7.5.x.src.rpm
Red Hat Linux 6.x:
alpha:
ftp://updates.redhat.com/6.2/en/os/alpha/lpr-0.50-7.6.x.alpha.rpm
sparc:
ftp://updates.redhat.com/6.2/en/os/sparc/lpr-0.50-7.6.x.sparc.rpm
i386:
ftp://updates.redhat.com/6.2/en/os/i386/lpr-0.50-7.6.x.i386.rpm
sources:
ftp://updates.redhat.com/6.2/en/os/SRPMS/lpr-0.50-7.6.x.src.rpm
6. Solution:
For each RPM for your particular architecture, run:
rpm -Fvh [filename]
where filename is the name of the RPM.
Additionally, after upgrading, you will want to restart your "lpd" service
by executing the following as root:
/etc/rc.d/init.d/lpd restart
If you do not need printing at all on your system, we recommend you remove
the lpr print system:
/etc/rc.d/init.d/lpd stop
rpm -e lpr
7. Verification:
MD5 sum Package Name
-------------------------------------------------------------------------
c4c0311c59fd741507a41ce6705d7b11 5.2/en/os/SRPMS/lpr-0.50-7.5.x.src.rpm
3ee5d7ae89389678c48a881ea9f13de3 5.2/en/os/alpha/lpr-0.50-7.5.x.alpha.rpm
1a516bb638568f516beda7dd98c8ee1b 5.2/en/os/i386/lpr-0.50-7.5.x.i386.rpm
73308d3778f5f9f953c794cecd98dde4 5.2/en/os/sparc/lpr-0.50-7.5.x.sparc.rpm
49d59ce8e0347a59a55ae10e142ad709 6.2/en/os/SRPMS/lpr-0.50-7.6.x.src.rpm
031b2bb377ec41ca2f1b924a0e92fad6 6.2/en/os/alpha/lpr-0.50-7.6.x.alpha.rpm
d1576d4478830b78f2368935eb59044a 6.2/en/os/i386/lpr-0.50-7.6.x.i386.rpm
031b953bd97f40e5b9f11696ac27c4d5 6.2/en/os/sparc/lpr-0.50-7.6.x.sparc.rpm
These packages are GPG signed by Red Hat, Inc. for security. Our key
is available at:
http://www.redhat.com/about/contact.html
You can verify each package with the following command:
rpm --checksig filename
If you only wish to verify that each package has not been corrupted or
tampered with, examine only the md5sum with the following command:
rpm --checksig --nogpg filename
Note that you need RPM >= 3.0 to check GnuPG keys.
8. References:
Thanks go to Chris Evans <chris@scary.beasts.org> for spotting this in the
OpenBSD lpr CVS commit logs, and verifying the problem existed for Linux as
well.
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