SuSE Linux Advisory: dhcp/dhcp server
May 22, 2002, 18:34 (0 Talkback[s])
SuSE Security Announcement
Date: Wednesday, May 22th 2002 13:30 MEST
Affected products: 7.2, 7.3, 8.0
SuSE Linux Database Server
SuSE eMail Server III
SuSE Linux Enterprise Server for S/390
SuSE Linux Connectivity Server
SuSE Linux Enterprise Server 7
Vulnerability Type: remote command execution
Severity (1-10): 4
SuSE default package: no
Other affected systems: all systems using ISC DHCP server 3.x
Content of this advisory:
1) security vulnerability resolved: format string bug in dynamic DNS
problem description, discussion, solution and upgrade information
2) pending vulnerabilities, solutions, workarounds
3) standard appendix (further information)
1) problem description, brief discussion, solution, upgrade information
The "Dynamic Host Configuration Protocol" (DHCP) server from the Internet
Software Consortium allows hosts on a TCP/IP network to request and be
assigned IP addresses, and also to discover information about the network
to which they are attached.
A remote exploitable format string vulnerability was found in the logging
routines of the dynamic DNS code of dhcpd. This vulnerability allows an
attacker, usually within the LAN served by the DHCP server, to get remote
root access to the host running dhcpd.
The dhcp/dhcp-server package is not installed by default nor is the
dynamic DNS feature enabled by default.
As temporary workaround the dynamic DNS feature could be disabled via
dhcpd's config file with the following lines:
After updating the package or modifying the config file you have to run:
as root to restart all instances of running dhcpd processes.
Please download the update package for your distribution and verify its
integrity by the methods listed in section 3) of this announcement.
Then, install the package using the command "rpm -Fhv file.rpm" to apply
Our maintenance customers are being notified individually. The packages
are being offered to install from the maintenance web.
i386 Intel Platform:
PPC Power PC Platform:
2) Pending vulnerabilities in SuSE Distributions and Workarounds:
Various security and non-security related bugs were found in the code
of tcpdump and libpcap. New RPMs are currently being build.
3) standard appendix: authenticity verification, additional information
- Package authenticity verification:
SuSE update packages are available on many mirror ftp servers all over
the world. While this service is being considered valuable and important
to the free and open source software community, many users wish to be
sure about the origin of the package and its content before installing
the package. 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) md5sums as provided in the (cryptographically signed) announcement.
2) using the internal gpg signatures of the rpm package.
1) execute the command
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
announcement. Since the announcement containing the checksums is
cryptographically signed (usually using the key firstname.lastname@example.org),
the checksums show proof of the authenticity of the package.
We disrecommend to subscribe to security lists which cause the
email message containing the announcement to be modified so that
the signature does not match after transport through the mailing
Downsides: You must be able to verify the authenticity of the
announcement in the first place. If RPM packages are being rebuilt
and a new version of a package is published on the ftp server, all
md5 sums for the files are useless.
2) 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, where <file.rpm> is the
filename of the rpm package that you have downloaded. Of course,
package authenticity verification can only target an uninstalled rpm
a) gpg is installed
b) The package is signed using a certain key. The public part of this
key must be installed by the gpg program in the directory
~/.gnupg/ under the user's home directory who performs the
signature verification (usually root). You can import the key
that is used by SuSE in rpm packages for SuSE Linux by saving
this announcement to a file ("announcement.txt") and
running the command (do "su -" to be root):
gpg --batch; gpg < announcement.txt | gpg --import
SuSE Linux distributions version 7.1 and thereafter install the
key "email@example.com" upon installation or upgrade, provided that
the package gpg is installed. The file containing the public key
is placed at the toplevel directory of the first CD (pubring.gpg)
and at ftp://ftp.suse.com/pub/suse/pubring.gpg-build.suse.de .
- SuSE runs two security mailing lists to which any interested party may
- general/linux/SuSE security discussion.
All SuSE security announcements are sent to this list.
To subscribe, send an email to
- SuSE's announce-only mailing list.
Only SuSE's security annoucements are sent to this list.
To subscribe, send an email to
For general information or the frequently asked questions (faq)
send mail to:
SuSE's security contact is <firstname.lastname@example.org> or <email@example.com>.
The <firstname.lastname@example.org> 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,
it is desired that the cleartext signature shows proof of the
authenticity of the text.
SuSE Linux AG makes no warranties of any kind whatsoever with respect
to the information contained in this security advisory.
Thomas Biege <email@example.com>
SuSE Linux AG,Deutschherrnstr. 15-19,90429 Nuernberg
Function: Security Support & Auditing
"lynx -source http://www.suse.de/~thomas/contact/thomas.asc | pgp -fka"
Key fingerprint = 51 AD B9 C7 34 FC F2 54 01 4A 1C D4 66 64 09 83
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