Potential DOS in Samba internal DNS server

Description

Samba versions 4.0.0 and above have a flaw in DNS protocol handling in the
internal DNS server. The server will not check the “reply” flag in the DNS
packet header when processing a request. That makes it vulnerable to reply
to a spoofed reply packet with another reply. Two affected servers could thus
DOS each other.

Patch Availability

Patches addressing this issue have been posted to:

http://www.samba.org/samba/security/

Samba version 4.0.18 includes a patch for this issue.

Workaround

Use the BIND_DLZ DNS backend to avoid this issue.

Credits

This problem was reported on IRC by a Samba user

Patch provided by Kai Blin of the Samba team.

== Our Code, Our Bugs, Our Responsibility.
== The Samba Team