net/samba4: update to 4.12.7

Update samba4 package to 4.12.7.


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                   Release Notes for Samba 4.12.7
                         September 18, 2020
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This is a security release 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

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