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These files are based on the BIND v9 ARM in FrameMaker. After these files are edited they will become the master source for the BIND v9 ARM. Still need to include style sheets and the actual XML DocBook DTD for those who do not have it.
82 lines
4.9 KiB
XML
82 lines
4.9 KiB
XML
<chapter><title><acronym>BIND</acronym> 9 Security Considerations</title>
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<sect1><title id="Access_Control_Lists">Access Control Lists</title>
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<para>Access Control Lists (ACLs), are address match lists that
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you can set up and nickname for future use in <command>allow-query</command>, <command>allow-recursion</command>, <command>blackhole</command>, <command>allow-transfer</command>,
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etc.</para>
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<para>Using ACLs allows you to have finer control over who can access
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your nameserver, without cluttering up your config files with huge
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lists of IP addresses.</para>
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<para>It is a <emphasis>good idea</emphasis> to use ACLs, and to
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control access to your server. Limiting access to your server by
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outside parties can help prevent spoofing and DoS attacks against
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your server.</para>
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<para>Here is an example of how to properly apply ACLs:</para>
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<programlisting>
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// Set up an ACL named "bogusnets" that will block RFC1918 space,
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// which is commonly used in spoofing attacks.
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acl bogusnets { 0.0.0.0/8; 1.0.0.0/8; 2.0.0.0/8; 192.0.2.0/24; 224.0.0.0/3; 10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16; };
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// Set up an ACL called our-nets. Replace this with the real IP numbers.
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acl our-nets { x.x.x.x/24; x.x.x.x/21; };
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options {
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...
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...
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allow-query { our-nets; };
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allow-recursion { our-nets; };
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...
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blackhole { bogusnets; };
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...
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};
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zone "example.com" {
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type master;
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file "m/example.com";
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allow-query { any; };
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};
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</programlisting>
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<para>This allows recursive queries of the server from the outside
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unless recursion has been previously disabled.</para>
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<para>For more information on how to use ACLs to protect your server,
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see the <emphasis>AUSCERT</emphasis> advisory at
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<ulink url="ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos">ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos</ulink></para></sect1>
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<sect1><title><command>chroot</command> and <command>setuid</command> (for
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UNIX servers)</title>
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<para>On UNIX servers, it is possible to run <acronym>BIND</acronym> in a <emphasis>chrooted</emphasis> environment
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(<command>chroot()</command>) by specifying the "<option>-t</option>"
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option. This can help improve system security by placing <acronym>BIND</acronym> in
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a "sandbox," which will limit the damage done if a server is compromised.</para>
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<para>Another useful feature in the UNIX version of <acronym>BIND</acronym> is the
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ability to run the daemon as a nonprivileged user ( <option>-u</option> <replaceable>user</replaceable> ).
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We suggest running as a nonprivileged user when using the <command>chroot</command> feature.</para>
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<para>Here is an example command line to load <acronym>BIND</acronym> in a <command>chroot()</command> sandbox,
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<command>/var/named</command>, and to run <command>named</command> <command>setuid</command> to
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user 202:</para>
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<para><userinput>/usr/local/bin/named -u 202 -t /var/named</userinput></para>
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<sect2><title>The <command>chroot</command> Environment</title>
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<para>In order for a <command>chroot()</command> environment to
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work properly in a particular directory (for example, <filename>/var/named</filename>),
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you will need to set up an environment that includes everything
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<acronym>BIND</acronym> needs to run. From <acronym>BIND</acronym>'s point of view, <filename>/var/named</filename> is
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the root of the filesystem. You will need <filename>/dev/null</filename>,
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and any library directories and files that <acronym>BIND</acronym> needs to run on
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your system. Please consult your operating system's instructions
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if you need help figuring out which library files you need to copy
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over to the <command>chroot()</command> sandbox.</para>
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<para>If you are running an operating system that supports static
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binaries, you can also compile <acronym>BIND</acronym> statically and avoid the need
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to copy system libraries over to your <command>chroot()</command> sandbox.</para></sect2>
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<sect2><title>Using the <command>setuid</command> Function </title>
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<para>Prior to running the <command>named</command> daemon, use
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the <command>touch</command> utility (to change file access and
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modification times) or the <command>chown</command> utility (to
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set the user id and/or group id) on files to which you want <acronym>BIND</acronym>
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to write.</para></sect2></sect1>
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<sect1><title>Dynamic Updates</title>
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<para>Access to the dynamic update facility should be strictly limited.
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In earlier versions of <acronym>BIND</acronym> the only way to do this was based on
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the IP address of the host requesting the update. <acronym>BIND9</acronym> also
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supports authenticating updates cryptographically by means of transaction
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signatures (TSIG). The use of TSIG is strongly recommended.</para>
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<para>Some sites choose to keep all dynamically updated DNS data
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in a subdomain and delegate that subdomain to a separate zone. This
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way, the top-level zone containing critical data such as the IP addresses
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of public web and mail servers need not allow dynamic update at
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all.</para></sect1></chapter>
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