[8598] in bugtraq
KDE Screensaver vulnerability
daemon@ATHENA.MIT.EDU (Christian Esken)
Wed Nov 18 16:47:58 1998
Date: Wed, 18 Nov 1998 23:11:06 +0100
Reply-To: Christian Esken <esken@KDE.ORG>
From: Christian Esken <esken@KDE.ORG>
To: BUGTRAQ@NETSPACE.ORG
Dear Bugtraq subscribers,
KDE Screensavers are usually running SUID root. Security issues have
been posted to Bugtraq on Nov 16 1998, under the subject "KDE 1.0's
klock can be used to gain root priveledges". The KDE team has now
published a fix for the KDE1.0 branch and the current branch.
With this change, screensavers and klock are not running SUID anymore.
This will solve every potential exploit, like misuse of buffer overruns
to gain root rights or executing a wrong executable under SUID rights.
The following text explains the technique used to solve the problem.
An advisory for distributors, users and administrators follows the
technical description.
Technique
---------
An authentification program, kcheckpass, has been introduced. This
is a separate, helper program, that runs SUID and is called each
time a password has to be checked. The password is passed via
STDIN to the program and the result of the authentification
process is returned in the return code of the program.
This program is small and supposed to be free from security hazzles.
Advisory
--------
Administrators should remove any SUID bit from KDE executables.
After updating to the fixed KDE1.0 tree or to the current KDE,
administrators should
1) check the access rights of the installed executables. The
screensavers must not be installed SUID anymore. If in doubt,
remove the SUID bits manually by a suitable command, like
"chmod -s *.kss klock" under Linux.
2) check the access rights of the kcheckpass program. This program
should only be installed SUID root under certain authentification
systems, like the shadow password suite.
3) Distributions using the shadow password system can be made more
secure by creating a "shadow" group and setting the access rights
of /etc/shadow and kcheckpass like in the following example:
-rw-r----- 1 root shadow 746 Sep 2 21:35 /etc/shadow
-rwxr-sr-x 1 root shadow 4720 Nov 17 22:32 /opt/kde/bin/kc=
heckpass
Distributors are strongly encouraged to follow this scheme. This
way, the kcheckpass is running under the effective user id of the us=
er
itself and the effective group "shadow". With this, kcheckpass has o=
nly
one additional right against regular users: The right to read /etc/s=
hadow.
Attackers won't be able to make wider use of "kcheckpass".
Availability of the fix
-----------------------
The patches are already integrated in the KDE1.0 and the KDE1.1 branche=
s.
You can use cvs/cvsup to get current sources. You can also get the patc=
h
from KDE's ftp Server ftp://ftp.kde.org and its mirrors, which you can =
apply
against a clean KDE1.0 kdebase package.
It has been uploaded under the name kdebase1.0-klock-patch and should
show up soon on a suitable place on KDE's ftp Server. The precise locat=
ion
will be announced later, for example http://www.kde.org/news_dyn.html w=
ill
provide this information as soon as it available.
Christian Esken <esken@kde.org>=FF
