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| From: | CERT <cert_(at)_cert.gov> | | Date: | 26.10.2002 | | Subject: | CERT Advisory CA-2002-29 Buffer Overflow in Kerberos Administration Daemon |
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CERT Advisory CA-2002-29 Buffer Overflow in Kerberos Administration Daemon
Original issue date: October 25, 2002
Last revised: --
Source: CERT/CC
A complete revision history is at the end of this file.
Systems Affected
* MIT Kerberos version 4 and version 5 up to and including
krb5-1.2.6
* KTH eBones prior to version 1.2.1 and KTH Heimdal prior to version
0.5.1
* Other Kerberos implementations derived from vulnerable MIT or KTH
code
Overview
Multiple Kerberos distributions contain a remotely exploitable buffer
overflow in the Kerberos administration daemon. A remote attacker
could exploit this vulnerability to gain root privileges on a
vulnerable system.
The CERT/CC has received reports that indicate that this vulnerability
is being exploited. In addition, MIT advisory MITKRB5-SA-2002-002
notes that an exploit is circulating.
We strongly encourage sites that use vulnerable Kerberos distributions
to verify the integrity of their systems and apply patches or upgrade
as appropriate.
I. Description
Kerberos is a widely used network protocol that uses strong
cryptography to authenticate clients and servers. The Kerberos
administration daemon (typically called kadmind) handles password
change and other requests to modify the Kerberos database. The daemon
runs on the master Key Distribution Center (KDC) server of a Kerberos
realm.
The code that provides legacy support for the Kerberos 4
administration protocol contains a remotely exploitable buffer
overflow. The vulnerable code does not adequately validate data read
from a network request. This data is subsequently used as an argument
to a memcpy() call, which can overflow a buffer allocated on the
stack. An attacker does not have to authenticate in order to exploit
this vulnerability, and the Kerberos administration daemon runs with
root privileges.
Both Massachusetts Institute of Technology (MIT) and Kungl Tekniska
HĐ–gskolan (KTH) Kerberos are affected, as well as operating systems,
applications, and other Kerberos implementations that use vulnerable
code derived from either the MIT or KTH distributions. In MIT Kerberos
5, the Kerberos 4 administration daemon is implemented in kadmind4. In
KTH Kerberos 4 (eBones), the Kerberos administration daemon is
implemented in kadmind. KTH Kerberos 5 (Heimdal) also implements the
daemon in kadmind; however, the Heimdal daemon is only affected if
compiled with Kerberos 4 support. Since the vulnerable Kerberos
administration daemon is included in the MIT Kerberos 5 and KTH
Heimdal distributions, both Kerberos 4 sites and Kerberos 5 sites that
enable support for the Kerberos 4 administration protocol are
affected.
Further information about this vulnerability may be found in
VU#875073.
MIT has released an advisory that contains information about this
vulnerability:
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2002-002-kadm
4.txt
The KTH eBones and Heimdal web sites also contain information about
this vulnerability:
KTH eBones
http://www.pdc.kth.se/kth-krb/
KTH Heimdal
http://www.pdc.kth.se/kth-krb/
In addition to resolving the vulnerability described in VU#875073,
version 0.51 of KTH Heimdal contains other fixes related to the KDC.
See the ChangeLog for more information:
ftp://ftp.pdc.kth.se/pub/heimdal/src/heimdal-0.5-0.5.1.diff.gz
This vulnerability has been assigned CAN-2002-1235 by the Common
Vulnerabilities and Exposures (CVE) group.
II. Impact
An unauthenticated, remote attacker could execute arbitrary code with
root privileges. If an attacker is able to gain control of a master
KDC, the integrity of the entire Kerberos realm is compromised,
including user and host identities and other systems that accept
Kerberos authentication.
III. Solution
Apply a patch or upgrade
Apply the appropriate patch or upgrade as specified by your vendor.
See Appendix A below and the Systems Affected section of VU#875073 for
specific information.
Disable vulnerable service
Disable support for the Kerberos 4 administration protocol if it is
not needed. In MIT Kerberos 5, this can be achieved by disabling
kadmind4. For information about disabling all Kerberos 4 support in
MIT Kerberos 5 at compile time, see
http://web.mit.edu/kerberos/www/krb5-1.2/krb5-1.2.6/doc/install.htm
l#SEC24
In KTH Heimdal, it is necessary to recompile kadmind in order to
disable support for the Kerberos 4 administration protocol. For
information about disabling all Kerberos 4 support in KTH Heimdal at
compile time, see
http://www.pdc.kth.se/heimdal/heimdal.html#Building%20and%20Install
ing
This solution will prevent Kerberos 4 administrative clients from
accessing the Kerberos database. It will also prevent users with
Kerberos 4 clients from changing their passwords. In general, the
CERT/CC recommends disabling any service that is not explicitly
required.
Block or restrict access
Block access to the Kerberos administration service from untrusted
networks such as the Internet. Furthermore, only allow access to the
service from trusted administrative hosts. By default, the Kerberos 4
administration daemon listens on 751/tcp and 751/udp, and the Kerberos
5 administration daemon listens on 749/tcp and 749/udp. It may be
necessary to block access to the Kerberos 5 administration service if
the daemon also supports the Kerberos 4 administration protocol. This
workaround will prevent administrative connections and password change
requests from blocked networks. Note that this workaround will not
prevent exploitation, but it will limit the possible sources of
attacks.
Appendix A. Vendor Information
This appendix contains information provided by vendors. When vendors
report new information, this section is updated and the changes are
noted in the revision history. If a vendor is not listed below, we
have not received their comments.
Apple Computer, Inc.
The Kerberos Administration Daemon was included in Mac OS X 10.0,
but removed in Mac OS X 10.1 and later.
We encourage sites that use vulnerable Kerberos distributions to
verify the integrity of their systems and apply patches or upgrade
as appropriate.
Conectiva
Our MIT Kerberos 5 packages in Conectiva Linux 8 do contain the
vulnerable kadmind4 daemon, but it is not used by default nor is it
installed as a service.
Updated packages are being uploaded to our ftp server and should be
available in a few hours at:
ftp://atualizacoes.conectiva.com.br/8/
The krb5-server-1.2.3-3U8_3cl.i386.rpm package contains a patched
kadmind4 daemon. An announcement will be sent to our security
mailing list a few hours after the upload is complete.
Debian
Debian has released DSA-178:
http://www.debian.org/security/2002/dsa-178
FreeBSD
Both the FreeBSD base Kerberos 4 (kadmind) and Kerberos 5 (k5admind
v4 compatibility) daemons were vulnerable and have been corrected
as of 23 October 2002. In addition, the heimdal and krb5 ports
contained the same vulnerability and have been corrected as of 24
October 2002. A Security Advisory is in progress.
KTH Kerberos
The eBones and Heimdal web sites have information about this
vulnerability:
KTH eBones
http://www.pdc.kth.se/kth-krb/
KTH Heimdal
http://www.pdc.kth.se/kth-krb/
Microsoft Corporation
Microsoft's implementation of Kerberos is not affected by this
vulnerability.
MIT Kerberos
MIT has released MIT krb5 Security Advisory 2002-002:
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2002-002-ka
dm4.txt
NetBSD
NetBSD has released NetBSD-SA2002-026:
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2002
-026.txt.asc
OpenBSD
OpenBSD has released Security Fix 016 for OpenBSD 3.1 and Security
Fix 033 for OpenBSD 3.0.
OpenBSD 3.1
http://www.openbsd.org/errata31.html#kadmin
OpenBSD 3.0
http://www.openbsd.org/errata30.html#kadmin
Openwall
Openwall GNU/*/Linux is not vulnerable. We don't provide Kerberos.
SuSE
SuSE Linux 7.2 and later are shipped with Heimdal Kerberos
included, but Kerberos 4 support is disabled in all releases.
Therefore, SuSE Linux and SuSE Enterprise Linux are not affected by
this bug. [See also: SuSE-SA:2002:034]
Wind River Systems (BSDI)
No version of BSD/OS is vulnerable to this problem.
Appendix B. References
* http://web.mit.edu/kerberos/www/
* http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2002-002-kad
m4.txt
* http://web.mit.edu/kerberos/www/krb5-1.2/krb5-1.2.6/doc/install.ht
ml#SEC24
* http://www.pdc.kth.se/kth-krb/
* http://www.pdc.kth.se/heimdal/
* http://www.pdc.kth.se/heimdal/heimdal.html#Building%20and%20Instal
ling
_________________________________________________________________
Authors: Art Manion and Jason A. Rafail.
______________________________________________________________________
This document is available from:
http://www.cert.org/advisories/CA-2002-29.html
______________________________________________________________________
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Revision History
October 25, 2002: Initial release
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