RHSA-2011:1854 - Security Advisory

Topic

Updated krb5-appl packages that fix one security issue are now available
for Red Hat Enterprise Linux 6.0 and 6.1 Extended Update Support.

The Red Hat Security Response Team has rated this update as having critical
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.

Description

The krb5-appl packages provide Kerberos-aware telnet, ftp, rcp, rsh, and
rlogin clients and servers. 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 buffer overflow flaw was found in the MIT krb5 telnet daemon (telnetd).
A remote attacker who can access the telnet port of a target machine could
use this flaw to execute arbitrary code as root. (CVE-2011-4862)

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 installed the krb5-appl-servers package, have enabled
the krb5 telnet daemon, and have it accessible remotely, this update should
be applied immediately.

All krb5-appl-server users should upgrade to these updated packages, which
contain a backported patch to correct this issue.

Solution

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

/sbin/chkconfig --list krb5-telnet
/sbin/chkconfig --list ekrb5-telnet

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

/sbin/chkconfig krb5-telnet off
/sbin/chkconfig ekrb5-telnet off

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
https://access.redhat.com/kb/docs/DOC-11259

Affected Products

• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.1 x86_64
• Red Hat Enterprise Linux for x86_64 - Extended Update Support 6.1 i386
• Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 6.1 s390x
• Red Hat Enterprise Linux for Power, big endian - Extended Update Support 6.1 ppc64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.1 x86_64
• Red Hat Enterprise Linux Server - Extended Update Support from RHUI 6.1 i386
• Red Hat Virtual Storage Appliance (from RHUI) 6.1 x86_64

Fixes

• BZ - 770325 - CVE-2011-4862 krb5: remote buffer overflow in kerberized telnet daemon

CVEs

• CVE-2011-4862

References

• https://access.redhat.com/security/updates/classification/#critical
• http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-008.txt