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AUSCERT External Security Bulletin Redistribution
Important: krb5 security and bug fix update
7 April 2010
AusCERT Security Bulletin Summary
Publisher: Red Hat
Operating System: Red Hat Enterprise Linux Server 5
Red Hat Enterprise Linux WS/Desktop 5
Impact/Access: Denial of Service -- Existing Account
CVE Names: CVE-2010-0629
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Red Hat Security Advisory
Synopsis: Important: krb5 security and bug fix update
Advisory ID: RHSA-2010:0343-01
Product: Red Hat Enterprise Linux
Advisory URL: https://rhn.redhat.com/errata/RHSA-2010-0343.html
Issue date: 2010-04-06
CVE Names: CVE-2010-0629
Updated krb5 packages that fix one security issue and one bug are now
available for Red Hat Enterprise Linux 5.
The Red Hat Security Response Team has rated this update as having
important security impact. A Common Vulnerability Scoring System (CVSS)
base score, which gives a detailed severity rating, is available from the
CVE link in the References section.
2. Relevant releases/architectures:
RHEL Desktop Workstation (v. 5 client) - i386, x86_64
Red Hat Enterprise Linux (v. 5 server) - i386, ia64, ppc, s390x, x86_64
Red Hat Enterprise Linux Desktop (v. 5 client) - i386, x86_64
Kerberos is a network authentication system which allows clients and
servers to authenticate to each other using symmetric encryption and a
trusted third party, the Key Distribution Center (KDC).
A use-after-free flaw was discovered in the MIT Kerberos administration
daemon, kadmind. A remote, authenticated attacker could use this flaw to
crash the kadmind daemon. Administrative privileges are not required to
trigger this flaw, as any realm user can request information about their
own principal from kadmind. (CVE-2010-0629)
This update also fixes the following bug:
* when a Kerberos client seeks tickets for use with a service, it must
contact the Key Distribution Center (KDC) to obtain them. The client must
also determine which realm the service belongs to and it typically does
this with a combination of client configuration detail, DNS information and
If the service belongs to a realm other than the client's, cross-realm
authentication is required. Using a combination of client configuration and
guesswork, the client determines the trust relationship sequence which
forms the trusted path between the client's realm and the service's realm.
This may include one or more intermediate realms.
Anticipating the KDC has better knowledge of extant trust relationships,
the client then requests a ticket from the service's KDC, indicating it
will accept guidance from the service's KDC by setting a special flag in
the request. A KDC which recognizes the flag can, at its option, return a
ticket-granting ticket for the next realm along the trust path the client
should be following.
If the ticket-granting ticket returned by the service's KDC is for use with
a realm the client has already determined was in the trusted path, the
client accepts this as an optimization and continues. If, however, the
ticket is for use in a realm the client is not expecting, the client
responds incorrectly: it treats the case as an error rather than continuing
along the path suggested by the service's KDC.
For this update, the krb5 1.7 modifications which allow the client to trust
such KDCs to send them along the correct path, resulting in the client
obtaining the tickets it originally desired, were backported to krb 1.6.1
(the version shipped with Red Hat Enterprise Linux 5.5). (BZ#578540)
All krb5 users should upgrade to these updated packages, which contain
backported patches to correct these issues. All running KDC services must
be restarted for the update to take effect.
Before applying this update, make sure all previously-released errata
relevant to your system have been applied.
This update is available via the Red Hat Network. Details on how to
use the Red Hat Network to apply this update are available at
5. Bugs fixed (http://bugzilla.redhat.com/):
576011 - CVE-2010-0629 krb5: kadmind use-after-free remote crash (MITKRB5-SA-2010-003)
578540 - [RFE] Backport referral-chasing code within krb5-1.7 to RHEL5
6. Package List:
Red Hat Enterprise Linux Desktop (v. 5 client):
RHEL Desktop Workstation (v. 5 client):
Red Hat Enterprise Linux (v. 5 server):
These packages are GPG signed by Red Hat for security. Our key and
details on how to verify the signature are available from
The Red Hat security contact is <firstname.lastname@example.org>. More contact
details at https://www.redhat.com/security/team/contact/
Copyright 2010 Red Hat, Inc.
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