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Home » Hacking News » SuSE-SA:2002:023-openssh


by Nikola Strahija on June 27th, 2002 Content of this advisory: 1) security vulnerability resolved: unknown vulnerability in the OpenSSH daemon. 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

There's a new vulnerabilty in the OpenSSH daemon, of which we were
notified yesterday.

The OpenSSH/OpenBSD team has asked Linux vendors to upgrade their
platforms to OpenSSH 3.3, and change the configuration to use the
relatively new "Privilege Separation" code. According to their
information, 3.3 does not fix the vulnerability, but using privilege
separation prevents exploits.

We were not given any additional information on the nature of the

Setting PrivilegeSeparation to on causes large portions of the
daemon to run in a so-called "chroot jail", i.e. in a very restricted
environment. An attacker breaking this part of the SSH daemon will
*not* obtain full root privilege (as he would if sshd ran without
this option), but will find himself in an empty directory, inside a
process running as a non privileged user (he can still do some harm
this way, but it's a far cry from full root powers).

The SuSE security team has prepared RPMs that upgrade OpenSSH to
version 3.3p1 on all SuSE Linux platforms. Based on the information
we've been given, we are unable to provide updates containing
a complete fix, nor can we guarantee that the workaround using
privilege separation is enough to protect you.

Given these imponderabilities, we suggest to you to take additional
precautions until details of the vulnerability have been published,
and we have been able to assess it:

- if you do not need external access to your SSH daemons,
turn off the SSH service on these machine completely, or block
external access at the firewall.

- if you do need external access to your SSH daemons,
make sure you restrict the hosts that it will talk to by setting
appropriate firewall rules.

If, for some reason, you cannot configure your firewall to
block external SSH access, you can also restrict access through
/etc/hosts.allow; the following will allow connections from
hosts with IP addresses, from hosts on the clas C IP
network, and from hosts in the DNS domain,
while rejecting any other connections.

sshd : : allow
sshd : : allow
sshd : * : allow
sshd : ALL : deny

As soon as we are given the relevant details, the SuSE security
team will publish a follow-up advisory, and another openssh
update, as required.

Please download the update package for your distribution and
verify its integrity by the methods listed in section 3) of this

If you are running nscd (enabled by default since SuSE Linux 7.0), the
name service caching daemon, shut down the daemon prior to upgrading
(this works around a bug in the groupadd command):

rcnscd stop

Then, install the package using the following command to apply
the update:

rpm -Fvh openssh*.rpm

After upgrading, please restart the SSH server by executing the
following command as super user:

rcsshd restart

Our maintenance customers are being notified individually. The
packages are being offered to install from the maintenance web.

Special notice concerning SuSE Linux 6.4 and 7.0:

SuSE Linux 6.4 ceased to be supported a week or two ago. However,
given the potential impact of this problem, we decided to issue update
packages for 6.4 as well. These are in the process of getting built,
and will show up on our FTP server soon.

Users of SuSE Linux 6.4 and 7.0, please also note that crypto update
packages for these platforms are always made available through only, not, due to the crypto laws that
were in effect in the US at the time of the original release of
the product.

i386 Intel Platform

source rpm:

source rpm:

source rpm:

source rpm:

source rpm:

Sparc Platform

source rpm:

source rpm:

source rpm:

AXP Alpha Platform

source rpm:

source rpm:

PPC Power PC Platform

source rpm:

source rpm:

source rpm:

2) Pending vulnerabilities in SuSE Distributions and Workarounds:

- mozilla
Cross-dependencies between mozilla and other packages in SuSE Linux
products keep us from providing version upgrades for the mozilla
packages. Fixing security bugs in our packages is usually done by
adding the necessary patches to the existing version to ensure the
compatibility and consistency that is expected from our products.
In some cases (as with the mozilla package) the complexity of the
issue does not allow to add patches any more. By consequence,
security related issues in mozilla cannot be addressed.
As a service to our user community, we provide packages of newer
mozilla versions at
These packages have been verified to run fine; they are not located
in the update directory of the distribution in question because
we cannot make any claims about the compatibility with the other
packages in the product. Security-aware users are encouraged to
install the packages from the projects/ directory.

- ghostscript
RedHat released a security announcement concerning a problem in
ghostscript, which could be exploited to gain privilege of the print
server user. We are investigating whether SuSE Linux is affected.

- kernel netfilter update
we are in the process of preparing a kernel update that will include
a security fix for a minor netfilter bug.

- fetchmail
we are in the process of releasing a security update for fetchmail
that corrects a vulnerability that could be exploited by hostile
mail servers.


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 [email protected]),
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
list software.
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
to verify the signature of the package, where is the
filename of the rpm package that you have downloaded. Of course,
package authenticity verification can only target an uninstalled rpm
package file.
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 .

[email protected]
- 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 or .
The 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

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