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Category:   Application (Security)  >   Kerberos Vendors:   MIT
(Red Hat Issues Fix) Kerberos Telnet Encryption Feature Buffer Overflow Lets Remote Users Execute Arbitrary Code
SecurityTracker Alert ID:  1026465
SecurityTracker URL:  http://securitytracker.com/id/1026465
CVE Reference:   CVE-2011-4862   (Links to External Site)
Date:  Dec 27 2011
Impact:   Execution of arbitrary code via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   A vulnerability was reported in Kerberos. A remote user can execute arbitrary code on the target system.

A remote user can supply a specially crafted encryption key to trigger a buffer overflow and execute arbitrary code on the target system. The code will run with the privileges of the telnet daemon (typically root privileges).

Versions prior to krb5-1.8 and all versions of krb5-appl are affected.

This vulnerability is being actively exploited.

[Editor's note: This vulnerability was previously reported in Alert ID 1026460 as also affecting FreeBSD telnetd.]

Impact:   A remote user can execute arbitrary code on the target system.
Solution:   Red Hat has issued a fix.

The Red Hat advisory is available at:

https://rhn.redhat.com/errata/RHSA-2011-1852.html

Vendor URL:  web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-008.txt (Links to External Site)
Cause:   Boundary error
Underlying OS:  Linux (Red Hat Enterprise)
Underlying OS Comments:  6

Message History:   This archive entry is a follow-up to the message listed below.
Dec 27 2011 Kerberos Telnet Encryption Feature Buffer Overflow Lets Remote Users Execute Arbitrary Code



 Source Message Contents

Subject:  [RHSA-2011:1852-02] Critical: krb5-appl security update

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=====================================================================
                   Red Hat Security Advisory

Synopsis:          Critical: krb5-appl security update
Advisory ID:       RHSA-2011:1852-02
Product:           Red Hat Enterprise Linux
Advisory URL:      https://rhn.redhat.com/errata/RHSA-2011-1852.html
Issue date:        2011-12-27
CVE Names:         CVE-2011-4862 
=====================================================================

1. Summary:

Updated krb5-appl packages that fix one security issue are now available
for Red Hat Enterprise Linux 6.

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.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Desktop (v. 6) - i386, x86_64
Red Hat Enterprise Linux HPC Node (v. 6) - x86_64
Red Hat Enterprise Linux Server (v. 6) - i386, ppc64, s390x, x86_64
Red Hat Enterprise Linux Workstation (v. 6) - i386, x86_64

3. 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.

4. 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 commands 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

5. Bugs fixed (http://bugzilla.redhat.com/):

770325 - CVE-2011-4862 krb5-appl: remote buffer overflow in kerberised telnet daemon

6. Package List:

Red Hat Enterprise Linux Desktop (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Client/en/os/SRPMS/krb5-appl-1.0.1-7.el6_2.src.rpm

i386:
krb5-appl-clients-1.0.1-7.el6_2.i686.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.i686.rpm
krb5-appl-servers-1.0.1-7.el6_2.i686.rpm

x86_64:
krb5-appl-clients-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-servers-1.0.1-7.el6_2.x86_64.rpm

Red Hat Enterprise Linux HPC Node (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6ComputeNode/en/os/SRPMS/krb5-appl-1.0.1-7.el6_2.src.rpm

x86_64:
krb5-appl-clients-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-servers-1.0.1-7.el6_2.x86_64.rpm

Red Hat Enterprise Linux Server (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Server/en/os/SRPMS/krb5-appl-1.0.1-7.el6_2.src.rpm

i386:
krb5-appl-clients-1.0.1-7.el6_2.i686.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.i686.rpm
krb5-appl-servers-1.0.1-7.el6_2.i686.rpm

ppc64:
krb5-appl-clients-1.0.1-7.el6_2.ppc64.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.ppc64.rpm
krb5-appl-servers-1.0.1-7.el6_2.ppc64.rpm

s390x:
krb5-appl-clients-1.0.1-7.el6_2.s390x.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.s390x.rpm
krb5-appl-servers-1.0.1-7.el6_2.s390x.rpm

x86_64:
krb5-appl-clients-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-servers-1.0.1-7.el6_2.x86_64.rpm

Red Hat Enterprise Linux Workstation (v. 6):

Source:
ftp://ftp.redhat.com/pub/redhat/linux/enterprise/6Workstation/en/os/SRPMS/krb5-appl-1.0.1-7.el6_2.src.rpm

i386:
krb5-appl-clients-1.0.1-7.el6_2.i686.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.i686.rpm
krb5-appl-servers-1.0.1-7.el6_2.i686.rpm

x86_64:
krb5-appl-clients-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-debuginfo-1.0.1-7.el6_2.x86_64.rpm
krb5-appl-servers-1.0.1-7.el6_2.x86_64.rpm

These packages are GPG signed by Red Hat for security.  Our key and 
details on how to verify the signature are available from
https://access.redhat.com/security/team/key/#package

7. References:

https://www.redhat.com/security/data/cve/CVE-2011-4862.html
https://access.redhat.com/security/updates/classification/#critical
http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-008.txt

8. Contact:

The Red Hat security contact is <secalert@redhat.com>.  More contact
details at https://access.redhat.com/security/team/contact/

Copyright 2011 Red Hat, Inc.
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