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CVE-2022-38023 docs-xml/smbdotconf: document "server reject md5 schannel:COMPUTERACCOUNT"
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15240 Signed-off-by: Stefan Metzmacher <metze@samba.org> Reviewed-by: Andrew Bartlett <abartlet@samba.org> Reviewed-by: Ralph Boehme <slow@samba.org>
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Stefan Metzmacher
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bd429d0259
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2ad302b422
@ -45,7 +45,9 @@
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in order to collect the explicit
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'<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT">yes</smbconfoption>' options.</para>
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<para>This option is over-ridden by the '<smbconfoption name="reject md5 clients">yes</smbconfoption>' option.</para>
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<para>This option is over-ridden by the effective value of 'yes' from
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the '<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT"/>'
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and/or '<smbconfoption name="reject md5 clients"/>' options.</para>
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</description>
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<value type="default">no</value>
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@ -85,12 +87,19 @@
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<para>This option overrides the <smbconfoption name="allow nt4 crypto"/> option.</para>
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<para>This option is over-ridden by the '<smbconfoption name="reject md5 clients">yes</smbconfoption>' option.</para>
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<para>This option is over-ridden by the effective value of 'yes' from
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the '<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT"/>'
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and/or '<smbconfoption name="reject md5 clients"/>' options.</para>
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<para>Which means '<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT">yes</smbconfoption>'
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is only useful in combination with '<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT">no</smbconfoption>'</para>
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<programlisting>
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allow nt4 crypto:LEGACYCOMPUTER1$ = yes
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server reject md5 schannel:LEGACYCOMPUTER1$ = no
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allow nt4 crypto:NASBOX$ = yes
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server reject md5 schannel:NASBOX$ = no
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allow nt4 crypto:LEGACYCOMPUTER2$ = yes
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server reject md5 schannel:LEGACYCOMPUTER2$ = no
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</programlisting>
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</description>
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@ -1,8 +1,15 @@
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<samba:parameter name="reject md5 clients"
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context="G"
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type="boolean"
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deprecated="1"
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xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
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<description>
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<para>
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This option is deprecated and will be removed in a future release,
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as it is a security problem if not set to "yes" (which will be
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the hardcoded behavior in the future).
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</para>
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<para>This option controls whether the netlogon server (currently
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only in 'active directory domain controller' mode), will
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reject clients which does not support NETLOGON_NEG_SUPPORTS_AES.</para>
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@ -10,13 +17,94 @@
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<para>Support for NETLOGON_NEG_SUPPORTS_AES was added in Windows
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starting with Server 2008R2 and Windows 7, it's available in Samba
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starting with 4.0, however third party domain members like NetApp ONTAP
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still uses RC4 (HMAC-MD5), see https://www.samba.org/samba/security/CVE-2022-38023.html for more details.</para>
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still uses RC4 (HMAC-MD5), see
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<ulink url="https://www.samba.org/samba/security/CVE-2022-38023.html">https://www.samba.org/samba/security/CVE-2022-38023.html</ulink>
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for more details.
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</para>
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<para>The default changed from 'no' to 'yes', with the patches for CVE-2022-38023,
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see https://bugzilla.samba.org/show_bug.cgi?id=15240</para>
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<para>The default changed from 'no' to 'yes', with the patches for
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<ulink url="https://www.samba.org/samba/security/CVE-2022-38023.html">CVE-2022-38023</ulink>
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see <ulink url="https://bugzilla.samba.org/show_bug.cgi?id=15240">https://bugzilla.samba.org/show_bug.cgi?id=15240</ulink>.
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</para>
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<para>This option overrides the 'allow nt4 crypto' option.</para>
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<para><emphasis>Avoid using this option!</emphasis> Use an explicit per machine account
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'<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT"/>' instead!
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Which is available with the patches for
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<ulink url="https://www.samba.org/samba/security/CVE-2022-38023.html">CVE-2022-38023</ulink>
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see <ulink url="https://bugzilla.samba.org/show_bug.cgi?id=15240">https://bugzilla.samba.org/show_bug.cgi?id=15240</ulink>.
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</para>
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<para>
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Samba will log an error in the log files at log level 0
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if legacy a client is rejected or allowed without an explicit,
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'<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT">no</smbconfoption>' option
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for the client. The message will indicate
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the explicit '<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT">no</smbconfoption>'
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line to be added, if the legacy client software requires it. (The log level can be adjusted with
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'<smbconfoption name="CVE_2022_38023:error_debug_level">1</smbconfoption>'
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in order to complain only at a higher log level).
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</para>
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<para>This allows admins to use "no" only for a short grace period,
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in order to collect the explicit
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'<smbconfoption name="server reject md5 schannel:COMPUTERACCOUNT">no</smbconfoption>' options.</para>
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<para>When set to 'yes' this option overrides the
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'<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT"/>' and
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'<smbconfoption name="allow nt4 crypto"/>' options and implies
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'<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT">no</smbconfoption>'.
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</para>
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</description>
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<value type="default">yes</value>
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</samba:parameter>
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<samba:parameter name="server reject md5 schannel:COMPUTERACCOUNT"
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context="G"
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type="string"
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xmlns:samba="http://www.samba.org/samba/DTD/samba-doc">
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<description>
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<para>If you still have legacy domain members or trusted domains,
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which required "reject md5 clients = no" before,
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it is possible to specify an explicit exception per computer account
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by setting 'server reject md5 schannel:COMPUTERACCOUNT = no'.
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Note that COMPUTERACCOUNT has to be the sAMAccountName value of
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the computer account (including the trailing '$' sign).
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</para>
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<para>
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Samba will log a complaint in the log files at log level 0
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about the security problem if the option is set to "no",
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but the related computer does not require it.
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(The log level can be adjusted with
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'<smbconfoption name="CVE_2022_38023:warn_about_unused_debug_level">1</smbconfoption>'
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in order to complain only at a higher log level).
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</para>
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<para>
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Samba will log a warning in the log files at log level 5
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if a setting is still needed for the specified computer account.
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</para>
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<para>
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See <ulink url="https://www.samba.org/samba/security/CVE-2022-38023.html">CVE-2022-38023</ulink>,
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<ulink url="https://bugzilla.samba.org/show_bug.cgi?id=15240">https://bugzilla.samba.org/show_bug.cgi?id=15240</ulink>.
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</para>
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<para>This option overrides the <smbconfoption name="reject md5 clients"/> option.</para>
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<para>When set to 'yes' this option overrides the
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'<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT"/>' and
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'<smbconfoption name="allow nt4 crypto"/>' options and implies
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'<smbconfoption name="allow nt4 crypto:COMPUTERACCOUNT">no</smbconfoption>'.
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</para>
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<programlisting>
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server reject md5 schannel:LEGACYCOMPUTER1$ = no
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server reject md5 schannel:NASBOX$ = no
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server reject md5 schannel:LEGACYCOMPUTER2$ = no
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</programlisting>
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</description>
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</samba:parameter>
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