Critical: krb5 security update

Updated krb5 packages that fix a number of issues are now available.

This update has been rated as having critical security impact by the Red
Hat Security Response Team.

Kerberos is a network authentication system which allows clients and
servers to authenticate to each other through use of symmetric encryption
and a trusted third party, the KDC.

A flaw was found in the username handling of the MIT krb5 telnet daemon
(telnetd). A remote attacker who can access the telnet port of a target
machine could log in as root without requiring a password. (CVE-2007-0956)

Note that the krb5 telnet daemon is not enabled by default in any version
of Red Hat Enterprise Linux. In addition, the default firewall rules block
remote access to the telnet port. This flaw does not affect the telnet
daemon distributed in the telnet-server package.

For users who have enabled the krb5 telnet daemon and have it accessible
remotely, this update should be applied immediately.

Whilst we are not aware at this time that the flaw is being actively
exploited, we have confirmed that the flaw is very easily exploitable.

This update also fixes two additional security issues:

Buffer overflows were found which affect the Kerberos KDC and the kadmin
server daemon. A remote attacker who can access the KDC could exploit this
bug to run arbitrary code with the privileges of the KDC or kadmin server
processes. (CVE-2007-0957)

A double-free flaw was found in the GSSAPI library used by the kadmin
server daemon. Red Hat Enterprise Linux 4 and 5 contain checks within
glibc that detect double-free flaws. Therefore, on Red Hat Enterprise Linux
4 and 5 successful exploitation of this issue can only lead to a denial of
service. Applications which use this library in earlier releases of Red
Hat Enterprise Linux may also be affected. (CVE-2007-1216)

All users are advised to update to these erratum packages which contain a
backported fix to correct these issues.

Red Hat would like to thank MIT and iDefense for reporting these
vulnerabilities.

The krb5 telnet daemon is an xinetd service. You can determine if krb5
telnetd is enabled with the command:

/sbin/chkconfig --list krb5-telnet

The output of this command will be "krb5-telnet on" if krb5 telnet is
enabled. krb5 telnet daemon can be immediately disabled with the command:

/sbin/chkconfig krb5-telnet off

Before applying this update, make sure that all previously-released
errata relevant to your system have been applied.

This update is available via Red Hat Network. Details on how to use
the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/FAQ_58_10188

229782 - CVE-2007-0956 Unauthorized access via krb5-telnet daemon
231528 - CVE-2007-0957 krb5_klog_syslog() stack buffer overflow
231537 - CVE-2007-1216 krb5 double free flaw

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-0956
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-0957
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-1216
http://www.redhat.com/security/updates/classification/#critical