Software 42424 Published by

The second release candidate for Samba 4.17.0 is now available for testing.  Samba is the standard Windows interoperability suite of programs for Linux and Unix.

Samba 4.17.0rc2 Available for Download

Release Announcements

This is the second release candidate of Samba 4.17.  This is *not* intended for production environments and is designed for testing purposes only.  Please report any defects via the Samba bug reporting system at

Samba 4.17 will be the next version of the Samba suite.




SMB Server performance improvements

The security improvements in recent releases
(4.13, 4.14, 4.15, 4.16), mainly as protection against symlink races, caused performance regressions for meta data heavy workloads.
With 4.17 the situation improved a lot again:

- Pathnames given by a client are devided into dirname and basename.   The amount of syscalls to validate dirnames is reduced to 2 syscalls   (openat, close) per component. On modern Linux kernels (>= 5.6) smbd   makes use of the openat2() syscall with RESOLVE_NO_SYMLINKS,   in order to just use 2 syscalls (openat2, close) for the whole dirname.
- Contended path based operations used to generate a lot of unsolicited   wakeup events causing thundering herd problems, which lead to masive   latencies for some clients. These events are now avoided in order   to provide stable latencies and much higher throughput of open/close   operations.

Configure without the SMB1 Server

It is now possible to configure Samba without support for
the SMB1 protocol in smbd. This can be selected at configure time with either of the options:


By default (without either of these options set) Samba
is configured to include SMB1 support (i.e. --with-smb1-server is the default). When Samba is configured without SMB1 support, none of the SMB1 code is included inside smbd except the minimal stub code needed to allow a client to connect as SMB1 and immediately negotiate the selected protocol into SMB2 (as a Windows server also allows).

None of the SMB1-only smb.conf parameters are removed when
configured without SMB1, but these parameters are ignored by the smbd server. This allows deployment without having to change an existing smb.conf file.

This option allows sites, OEMs and integrators to configure Samba to remove the old and insecure SMB1 protocol from their products.
Note that the Samba client libraries still support SMB1 connections even when Samba is configured as --without-smb1-server. This is to ensure maximum compatibility with environments containing old SMB1 servers.

Bronze bit and S4U support with MIT Kerberos 1.20

In 2020 Microsoft Security Response Team received another Kerberos-related report. Eventually, that led to a security update of the CVE-2020-17049, Kerberos KDC Security Feature Bypass Vulnerability, also known as a ‘Bronze
Bit’. With this vulnerability, a compromised service that is configured to use
Kerberos constrained delegation feature could tamper with a service ticket that
is not valid for delegation to force the KDC to accept it.

With the release of MIT Kerberos 1.20, Samba AD DC is able able to mitigate the
‘Bronze Bit’ attack. MIT Kerberos KDC's KDB (Kerberos Database Driver) API was
changed to allow passing more details between KDC and KDB components. When built
against MIT Kerberos, Samba AD DC supports MIT Kerberos 1.19 and 1.20 versions
but 'Bronze Bit' mitigation is provided only with MIT Kerberos 1.20.
In addition to fixing the ‘Bronze Bit’ issue, Samba AD DC now fully supports
S4U2Self and S4U2Proxy Kerberos extensions.

Resource Based Constrained Delegation (RBCD) support

Samba AD DC built with MIT Kerberos 1.20 offers RBCD support now. With MIT Kerberos 1.20 we have complete RBCD support passing Sambas S4U testsuite. Note that samba-tool lacks support for setting this up yet!
To complete RBCD support and make it useful to Administrators we added the Asserted Identity [1] SID into the PAC for constrained delegation. This is available for Samba AD compiled with MIT Kerberos 1.20.


Customizable DNS listening port

It is now possible to set a custom listening port for the builtin DNS service,
making easy to host another DNS on the same system that would bind to the default port and forward the domain-specific queries to Samba using the custom
port. This is the opposite configuration of setting a forwarder in Samba.
It makes possible to use another DNS server as a front and forward to Samba.
Dynamic DNS updates may not be proxied by the front DNS server when forwarding
to Samba. Dynamic DNS update proxying depends on the features of the other DNS
server used as a front.

CTDB changes

* When Samba is configured with both --with-cluster-support and   --systemd-install-services then a systemd service file for CTDB will   be installed.

* ctdbd_wrapper has been removed.  ctdbd is now started directly from   a systemd service file or init script.

* The syntax for the ctdb.tunables configuration file has been   relaxed.  However, trailing garbage after the value, including   comments, is no longer permitted.  Please see ctdb-tunables(7) for   more details.

Operation without the (unsalted) NT password hash

When Samba is configured with 'nt hash store = never' then Samba will no longer store the (unsalted) NT password hash for users in Active Directory.  (Trust accounts, like computers, domain controllers and inter-domain trusts are not impacted).

In the next version of Samba the default for 'nt hash store' will change from 'always' to 'auto', where it will follow (behave as 'nt hash store = never' when 'ntlm auth = disabled' is set.

Security-focused deployments of Samba that have eliminated NTLM from their networks will find setting 'ntlm auth = disabled' with 'nt hash store = always' as a useful way to improve compliance with
best-practice guidance on password storage (which is to always use an interated hash).

Note that when 'nt hash store = never' is set, then arcfour-hmac-md5 Kerberos keys will not be available for users who subsequently change their password, as these keys derive their values from NT hashes. AES keys are stored by default for all deployments of Samba with Domain Functional Level 2008 or later, are supported by all modern clients, and are much more secure.

Finally, also note that password history in Active Directory is stored in nTPwdHistory using a series of NT hash values.  Therefore the full password history feature is not available in this mode.

To provide some protection against password re-use previous Kerberos hash values (the current, old and older values are already stored) are used, providing a history length of 3.

There is one small limitation of this workaround: Changing the sAMAccountName, userAccountControl or userPrincipalName of an account can cause the Kerberos password salt to change.  This means that after *both* an account rename and a password change, only the current password will be recognised for password history purposes.

Python API for smbconf

Samba's smbconf library provides a generic frontend to various configuration backends (plain text file, registry) as a C library. A new Python wrapper, importable as 'samba.smbconf' is available. An additional module, 'samba.samba3.smbconf', is also available to enable registry backend support. These libraries allow Python programs to read, and optionally write, Samba configuration natively.

JSON support for smbstatus

It is now possible to print detailed information in JSON format in the smbstatus program using the new option --json. The JSON output covers all the existing text output including sessions, connections, open files, byte-range locks, notifies and profile data with all low-level information maintained by Samba in the respective databases.


LanMan Authentication and password storage removed from the AD DC -----------------------------------------------------------------

The storage and authentication with LanMan passwords has been entirely removed from the Samba AD DC, even when "lanman auth = yes" is set.
smb.conf changes

  Parameter Name                          Description     Default
  --------------                          -----------     -------

  dns port                                New default     53
  nt hash store                  New parameter   always

o  Jeremy Allison
   * BUG 15143: New filename parser doesn't check veto files smb.conf parameter.
   * BUG 15144: 4.17.rc1 still uses symlink-race prone unix_convert()    * BUG 15146: Backport fileserver related changed to 4.17.0rc2
o  Jule Anger
   * BUG 15147: Manpage for smbstatus json is missing

o  Volker Lendecke
   * BUG 15146: Backport fileserver related changed to 4.17.0rc2
o  Stefan Metzmacher
   * BUG 15125: Performance regression on contended path based operations   * BUG 15146: Backport fileserver related changed to 4.17.0rc2
o  Andreas Schneider
   * BUG 15140: Fix issues found by coverity in smbstatus json code    * BUG 15146: Backport fileserver related changed to 4.17.0rc2


Reporting bugs & Development Discussion

Please discuss this release on the samba-technical mailing list or by joining the matrix room, or
#samba-technical IRC channel on

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 (

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


Download Details

The uncompressed tarballs and patch files have been signed
using GnuPG (ID AA99442FB680B620).  The source code can be downloaded from:

The release notes are available online at:
Our Code, Our Bugs, Our Responsibility.

                        The Samba Team