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Category:   OS (UNIX)  >   FreeBSD Kernel Vendors:   FreeBSD
FreeBSD Heimdal Programming Error Lets Remote Users Bypass Kerberos Authentication in Certain Cases
SecurityTracker Alert ID:  1038876
SecurityTracker URL:
CVE Reference:   CVE-2017-11103   (Links to External Site)
Date:  Jul 12 2017
Impact:   Host/resource access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 10.3, 11.0, 11.1
Description:   A vulnerability was reported in FreeBSD Heimdal. A remote user can bypass authentication in certain cases.

The KDC-REP service uses the plain text service name supplied in a ticket without authenticating the value. A remote user that can conduct a man-in-the-middle attack can bypass Kerberos mutual authentication.

Kerberos-enabled clients are affected.

Impact:   A remote user that can conduct a man-in-the-middle attack can bypass Kerberos mutual authentication.
Solution:   FreeBSD has issued a fix.

The FreeBSD advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Authentication error

Message History:   None.

 Source Message Contents

Subject:  FreeBSD Security Advisory FreeBSD-SA-17:05.heimdal

Hash: SHA512

FreeBSD-SA-17:05.heimdal                                    Security Advisory
                                                          The FreeBSD Project

Topic:          heimdal KDC-REP service name validation vulnerability

Category:       contrib
Module:         heimdal
Announced:      2017-07-12
Affects:        All supported versions of FreeBSD.
Corrected:      2017-07-12 07:26:07 UTC (stable/11, 11.1-PRERELEASE)
                2017-07-12 08:07:16 UTC (releng/11.1, 11.1-RC2-p1)
                2017-07-12 08:07:16 UTC (releng/11.1, 11.1-RC1-p1)
                2017-07-12 07:26:07 UTC (stable/11, 11.1-BETA3-p1)
                2017-07-12 08:07:36 UTC (releng/11.0, 11.0-RELEASE-p11)
                2017-07-12 07:26:07 UTC (stable/10, 10.3-STABLE)
                2017-07-12 15:16:01 UTC (releng/10.3, 10.3-RELEASE-p20)
CVE Name:       CVE-2017-11103

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:>.

I.   Background

Heimdal implements the Kerberos 5 network authentication protocols.
The Kerberos protocol uses "tickets" to authenticate a client to a

A Key Distribution Center (KDC) is trusted by all principals registered
in that administrative "realm" to store a secret key in confidence, of
which, the proof of knowledge is used to verify the authenticity of a

II.  Problem Description

There is a programming error in the Heimdal implementation that used an
unauthenticated, plain-text version of the KDC-REP service name found
in a ticket.

III. Impact

An attacker who has control of the network between a client and the
service it talks to will be able to impersonate the service, allowing
a successful man-in-the-middle (MITM) attack that circumvents the mutual

IV.  Workaround

No workaround is available, but only Kerberos enabled clients are

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.

A reboot is recommended.

2) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

A reboot is recommended.

3) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch
# fetch
# gpg --verify heimdal.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:>.

Restart all daemons that use the library, or reboot the system.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/10/                                                        r320907
releng/10.3/                                                      r320915
stable/11/                                                        r320907
releng/11.0/                                                      r320911
releng/11.1/                                                      r320910
- -------------------------------------------------------------------------

To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:

# svn diff -cNNNNNN --summarize svn://

Or visit the following URL, replacing NNNNNN with the revision number:


VII. References



The latest revision of this advisory is available at
Version: GnuPG v2.1.21 (FreeBSD)

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