Orpheus' Lyre mutual authentication validation bypass

Description

All versions of Samba from 4.0.0 include an embedded copy of Heimdal
Kerberos. Heimdal has made a security release, which disclosed:

Fix CVE-2017-11103: Orpheus’ Lyre KDC-REP service name validation

This is a critical vulnerability.

In _krb5_extract_ticket() the KDC-REP service name must be obtained from
encrypted version stored in ‘enc_part’ instead of the unencrypted version
stored in ‘ticket’. Use of the unecrypted version provides an
opportunity for successful server impersonation and other attacks.

Identified by Jeffrey Altman, Viktor Duchovni and Nico Williams.

See https://www.orpheus-lyre.info/ for more details.

The impact for Samba is particularly strong for cases where the Samba
DRS replication service contacts another DC requesting replication
of user passwords, as these could then be controlled by the attacker.

Patch Availability

A patch addressing this defect has been posted to

https://www.samba.org/samba/security/

Additionally, Samba 4.6.6, 4.5.12 and 4.4.15 have been issued as security
releases to correct the defect. Samba vendors and administrators running
affected versions linked against the embedded Heimdal Kerberos are advised to
upgrade or apply the patch as soon as possible.

Workaround

Samba versions built against MIT Kerberos are not impacted. Unless
you are running Samba as an AD DC, then rebuild samba using:

./configure --with-system-mitkrb5.

Credits

This problem was identified in Heimdal by Jeffrey Altman, Viktor
Duchovni and Nico Williams.

Andrew Bartlett, Garming Sam and Bob Campbell of Catalyst and the
Samba Team ported the fix to Samba and wrote this advisory.