#14047 closed enhancement (fixed)

Samba-4.12.7 (Urgent security release)

Reported by: Douglas R. Reno Owned by: Douglas R. Reno
Priority: highest Milestone: 10.1
Component: BOOK Version: SVN
Severity: normal Keywords:
Cc:

Description

CVE-2020-1472 (Unauthenticated domain takeover via netlogon ("ZeroLogon")), affects our version of Samba (and this is a protocol level flaw). Samba File Server will need modifications to continue to talk to Active Directory domains, so this directly affects us.

CVE-2020-1472 has been rated a 10.0/10.0 by the United States National Vulnerability Database.

Here is the release announcement:

Release Announcements
---------------------

These are security releases in order to address the following defect:

o CVE-2020-1472: Unauthenticated domain takeover via netlogon ("ZeroLogon").

The following applies to Samba used as domain controller only (most
seriously the Active Directory DC, but also the classic/NT4-style DC).

Installations running Samba as a file server only are not directly
affected by this flaw, though they may need configuration changes to
continue to talk to domain controllers (see "file servers and domain
members" below).

The netlogon protocol contains a flaw that allows an authentication
bypass. This was reported and patched by Microsoft as CVE-2020-1472.
Since the bug is a protocol level flaw, and Samba implements the
protocol, Samba is also vulnerable.

However, since version 4.8 (released in March 2018), the default
behaviour of Samba has been to insist on a secure netlogon channel,
which is a sufficient fix against the known exploits. This default is
equivalent to having 'server schannel = yes' in the smb.conf.

Therefore versions 4.8 and above are not vulnerable unless they have
the smb.conf lines 'server schannel = no' or 'server schannel = auto'.

Samba versions 4.7 and below are vulnerable unless they have 'server
schannel = yes' in the smb.conf.

Note each domain controller needs the correct settings in its smb.conf.

Vendors supporting Samba 4.7 and below are advised to patch their
installations and packages to add this line to the [global] section if
their smb.conf file.

The 'server schannel = yes' smb.conf line is equivalent to Microsoft's
'FullSecureChannelProtection=1' registry key, the introduction of
which we understand forms the core of Microsoft's fix.

Some domains employ third-party software that will not work with a
'server schannel = yes'. For these cases patches are available that
allow specific machines to use insecure netlogon. For example, the
following smb.conf:

   server schannel = yes
   server require schannel:triceratops$ = no
   server require schannel:greywacke$ = no

will allow only "triceratops$" and "greywacke$" to avoid schannel.

More details can be found here:
https://www.samba.org/samba/security/CVE-2020-1472.html


Changes:
--------

o  Jeremy Allison <jra@samba.org>
   * BUG 14497: CVE-2020-1472(ZeroLogon): s3:rpc_server/netlogon: Protect
     netr_ServerPasswordSet2 against unencrypted passwords.

o  Günther Deschner <gd@samba.org>
   * BUG 14497: CVE-2020-1472(ZeroLogon): s3:rpc_server/netlogon: Support
     "server require schannel:WORKSTATION$ = no" about unsecure configurations.

o  Gary Lockyer <gary@catalyst.net.nz>
   * BUG 14497: CVE-2020-1472(ZeroLogon): s4 torture rpc: repeated bytes in
     client challenge.

o  Stefan Metzmacher <metze@samba.org>
   * BUG 14497: CVE-2020-1472(ZeroLogon): libcli/auth: Reject weak client
     challenges in netlogon_creds_server_init()
     "server require schannel:WORKSTATION$ = no".


#######################################
Reporting bugs & Development Discussion
#######################################

Please discuss this release on the samba-technical mailing list or by
joining the #samba-technical IRC channel on irc.freenode.net.

If you do report problems then please try to send high quality
feedback. If you don't provide vital information to help us track down
the problem then you will probably be ignored.  All bug reports should
be filed under the Samba 4.1 and newer product in the project's Bugzilla
database (https://bugzilla.samba.org/).


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



================
Download Details
================

The uncompressed tarballs and patch files have been signed
using GnuPG (ID 6F33915B6568B7EA).  The source code can be downloaded
from:

        https://download.samba.org/pub/samba/stable/

The release notes are available online at:

        https://www.samba.org/samba/history/samba-4.12.7.html
        https://www.samba.org/samba/history/samba-4.11.13.html
        https://www.samba.org/samba/history/samba-4.10.18.html

Our Code, Our Bugs, Our Responsibility.
(https://bugzilla.samba.org/)

                        --Enjoy
                        The Samba Team

Change History (4)

comment:1 by Douglas R. Reno, 10 months ago

Owner: changed from blfs-book to Douglas R. Reno
Priority: normalhighest
Status: newassigned
The netlogon protocol contains a flaw that allows an authentication
bypass. This was reported and patched by Microsoft as CVE-2020-1472.
Since the bug is a protocol level flaw, and Samba implements the
protocol, Samba is also vulnerable.

comment:2 by Douglas R. Reno, 10 months ago

The buildfix sed is no longer required.

comment:3 by Douglas R. Reno, 10 months ago

Never mind, wasn't needed in a build without tests, but still is if you have "--enable-selftest" passed to it.

comment:4 by Douglas R. Reno, 10 months ago

Resolution: fixed
Status: assignedclosed

Fixed at r23741. An email has been sent, and errata has been added.

Note: See TracTickets for help on using tickets.