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c10c16dec587a0662068f6e2991c29ed3a9db943Richard Lowe - Copyright (C) 2004-2009 Internet Systems Consortium, Inc. ("ISC")
c10c16dec587a0662068f6e2991c29ed3a9db943Richard Lowe - Copyright (C) 2000-2003 Internet Software Consortium.
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c10c16dec587a0662068f6e2991c29ed3a9db943Richard Lowe - purpose with or without fee is hereby granted, provided that the above
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a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<title>Chapter�7.�BIND 9 Security Considerations</title>
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a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<tr><th colspan="3" align="center">Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</th></tr>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<td width="20%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h2 class="title">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="Bv9ARM.ch07"></a>Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</h2></div></div></div>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<dt><span class="sect1"><a href="Bv9ARM.ch07.html#Access_Control_Lists">Access Control Lists</a></span></dt>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<dt><span class="sect1"><a href="Bv9ARM.ch07.html#id2599326"><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span></a></span></dt>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2599408">The <span><strong class="command">chroot</strong></span> Environment</a></span></dt>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2599467">Using the <span><strong class="command">setuid</strong></span> Function</a></span></dt>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<dt><span class="sect1"><a href="Bv9ARM.ch07.html#dynamic_update_security">Dynamic Update Security</a></span></dt>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h2 class="title" style="clear: both">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="Access_Control_Lists"></a>Access Control Lists</h2></div></div></div>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Access Control Lists (ACLs) are address match lists that
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov you can set up and nickname for future use in <span><strong class="command">allow-notify</strong></span>,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span><strong class="command">allow-query</strong></span>, <span><strong class="command">allow-query-on</strong></span>,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span><strong class="command">allow-recursion</strong></span>, <span><strong class="command">allow-recursion-on</strong></span>,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span><strong class="command">blackhole</strong></span>, <span><strong class="command">allow-transfer</strong></span>,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Using ACLs allows you to have finer control over who can access
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov your name server, without cluttering up your config files with huge
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov lists of IP addresses.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov It is a <span class="emphasis"><em>good idea</em></span> to use ACLs, and to
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov control access to your server. Limiting access to your server by
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov outside parties can help prevent spoofing and denial of service (DoS) attacks against
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov your server.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Here is an example of how to properly apply ACLs:
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov// Set up an ACL named "bogusnets" that will block
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov// RFC1918 space and some reserved space, which is
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov// commonly used in spoofing attacks.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankovacl bogusnets {
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov// Set up an ACL called our-nets. Replace this with the
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov// real IP numbers.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov allow-query { our-nets; };
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov allow-recursion { our-nets; };
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov blackhole { bogusnets; };
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov type master;
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov allow-query { any; };
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov This allows recursive queries of the server from the outside
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov unless recursion has been previously disabled.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov For more information on how to use ACLs to protect your server,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov see the <span class="emphasis"><em>AUSCERT</em></span> advisory at:
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <a href="ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos" target="_top">ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos</a>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h2 class="title" style="clear: both">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="id2599326"></a><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov On UNIX servers, it is possible to run <acronym class="acronym">BIND</acronym>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov in a <span class="emphasis"><em>chrooted</em></span> environment (using
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov the <span><strong class="command">chroot()</strong></span> function) by specifying
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov the "<code class="option">-t</code>" option for <span><strong class="command">named</strong></span>.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov This can help improve system security by placing
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <acronym class="acronym">BIND</acronym> in a "sandbox", which will limit
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov the damage done if a server is compromised.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Another useful feature in the UNIX version of <acronym class="acronym">BIND</acronym> is the
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ).
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov We suggest running as an unprivileged user when using the <span><strong class="command">chroot</strong></span> feature.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Here is an example command line to load <acronym class="acronym">BIND</acronym> in a <span><strong class="command">chroot</strong></span> sandbox,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span><strong class="command">/var/named</strong></span>, and to run <span><strong class="command">named</strong></span> <span><strong class="command">setuid</strong></span> to
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <strong class="userinput"><code>/usr/local/sbin/named -u 202 -t /var/named</code></strong>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h3 class="title">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="id2599408"></a>The <span><strong class="command">chroot</strong></span> Environment</h3></div></div></div>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov In order for a <span><strong class="command">chroot</strong></span> environment
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov work properly in a particular directory
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov (for example, <code class="filename">/var/named</code>),
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov you will need to set up an environment that includes everything
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <acronym class="acronym">BIND</acronym> needs to run.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov From <acronym class="acronym">BIND</acronym>'s point of view, <code class="filename">/var/named</code> is
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov the root of the filesystem. You will need to adjust the values of
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov options like
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov like <span><strong class="command">directory</strong></span> and <span><strong class="command">pid-file</strong></span> to account
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Unlike with earlier versions of BIND, you typically will
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span class="emphasis"><em>not</em></span> need to compile <span><strong class="command">named</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov statically nor install shared libraries under the new root.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov However, depending on your operating system, you may need
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov to set up things like
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h3 class="title">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="id2599467"></a>Using the <span><strong class="command">setuid</strong></span> Function</h3></div></div></div>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Prior to running the <span><strong class="command">named</strong></span> daemon,
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov the <span><strong class="command">touch</strong></span> utility (to change file
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov modification times) or the <span><strong class="command">chown</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov to which you want <acronym class="acronym">BIND</acronym>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Note that if the <span><strong class="command">named</strong></span> daemon is running as an
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov unprivileged user, it will not be able to bind to new restricted
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov ports if the server is reloaded.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<div class="titlepage"><div><div><h2 class="title" style="clear: both">
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a name="dynamic_update_security"></a>Dynamic Update Security</h2></div></div></div>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Access to the dynamic
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov update facility should be strictly limited. In earlier versions of
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <acronym class="acronym">BIND</acronym>, the only way to do this was
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov based on the IP
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov address of the host requesting the update, by listing an IP address
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov network prefix in the <span><strong class="command">allow-update</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov zone option.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov This method is insecure since the source address of the update UDP
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov is easily forged. Also note that if the IP addresses allowed by the
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov <span><strong class="command">allow-update</strong></span> option include the
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov address of a slave
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov server which performs forwarding of dynamic updates, the master can
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov trivially attacked by sending the update to the slave, which will
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov forward it to the master with its own source IP address causing the
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov master to approve it without question.
fe77cc0407fb667ddc04e1a8f2e203bb7b9c80e1Robert Mustacchi For these reasons, we strongly recommend that updates be
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov cryptographically authenticated by means of transaction signatures
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov (TSIG). That is, the <span><strong class="command">allow-update</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov option should
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov list only TSIG key names, not IP addresses or network
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov prefixes. Alternatively, the new <span><strong class="command">update-policy</strong></span>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov option can be used.
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov Some sites choose to keep all dynamically-updated DNS data
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov in a subdomain and delegate that subdomain to a separate zone. This
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov way, the top-level zone containing critical data such as the IP
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov of public web and mail servers need not allow dynamic update at
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<td width="40%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<td width="40%" align="left" valign="top">Chapter�6.�<acronym class="acronym">BIND</acronym> 9 Configuration Reference�</td>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td>
a9478106a12424322498e53cf7cd75bd8a4d6004Yuri Pankov<td width="40%" align="right" valign="top">�Chapter�8.�Troubleshooting</td>