Bv9ARM.ch07.html revision 3b4098640dd85040270f39b9a5ee5e22de99d3d6
220N/A<!--
220N/A - Copyright (C) 2004-2006 Internet Systems Consortium, Inc. ("ISC")
220N/A - Copyright (C) 2000-2003 Internet Software Consortium.
220N/A -
220N/A - Permission to use, copy, modify, and distribute this software for any
220N/A - purpose with or without fee is hereby granted, provided that the above
220N/A - copyright notice and this permission notice appear in all copies.
220N/A -
220N/A - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
220N/A - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
220N/A - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
220N/A - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
220N/A - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
220N/A - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
220N/A - PERFORMANCE OF THIS SOFTWARE.
220N/A-->
220N/A<!-- $Id: Bv9ARM.ch07.html,v 1.112 2006/01/06 01:55:39 marka Exp $ -->
220N/A<html>
220N/A<head>
220N/A<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
220N/A<title>Chapter�7.�BIND 9 Security Considerations</title>
220N/A<meta name="generator" content="DocBook XSL Stylesheets V1.69.1">
5680N/A<link rel="start" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
220N/A<link rel="up" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
5680N/A<link rel="prev" href="Bv9ARM.ch06.html" title="Chapter�6.�BIND 9 Configuration Reference">
220N/A<link rel="next" href="Bv9ARM.ch08.html" title="Chapter�8.�Troubleshooting">
220N/A</head>
220N/A<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
220N/A<div class="navheader">
220N/A<table width="100%" summary="Navigation header">
220N/A<tr><th colspan="3" align="center">Chapter�7.�<span class="acronym">BIND</span> 9 Security Considerations</th></tr>
844N/A<tr>
844N/A<td width="20%" align="left">
220N/A<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td>
220N/A<th width="60%" align="center">�</th>
2899N/A<td width="20%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
2899N/A</td>
5680N/A</tr>
5680N/A</table>
220N/A<hr>
5715N/A</div>
5715N/A<div class="chapter" lang="en">
5715N/A<div class="titlepage"><div><div><h2 class="title">
514N/A<a name="Bv9ARM.ch07"></a>Chapter�7.�<span class="acronym">BIND</span> 9 Security Considerations</h2></div></div></div>
514N/A<div class="toc">
514N/A<p><b>Table of Contents</b></p>
5123N/A<dl>
5680N/A<dt><span class="sect1"><a href="Bv9ARM.ch07.html#Access_Control_Lists">Access Control Lists</a></span></dt>
5680N/A<dt><span class="sect1"><a href="Bv9ARM.ch07.html#id2573062"><span><strong class="command">chroot</strong></span> and <span><strong class="command">setuid</strong></span></a></span></dt>
5680N/A<dd><dl>
5680N/A<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2573274">The <span><strong class="command">chroot</strong></span> Environment</a></span></dt>
5680N/A<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2573402">Using the <span><strong class="command">setuid</strong></span> Function</a></span></dt>
5680N/A</dl></dd>
5680N/A<dt><span class="sect1"><a href="Bv9ARM.ch07.html#dynamic_update_security">Dynamic Update Security</a></span></dt>
5680N/A</dl>
5123N/A</div>
5715N/A<div class="sect1" lang="en">
5715N/A<div class="titlepage"><div><div><h2 class="title" style="clear: both">
5715N/A<a name="Access_Control_Lists"></a>Access Control Lists</h2></div></div></div>
5715N/A<p>
5715N/A Access Control Lists (ACLs), are address match lists that
220N/A you can set up and nickname for future use in <span><strong class="command">allow-notify</strong></span>,
220N/A <span><strong class="command">allow-query</strong></span>, <span><strong class="command">allow-recursion</strong></span>,
5680N/A <span><strong class="command">blackhole</strong></span>, <span><strong class="command">allow-transfer</strong></span>,
5715N/A etc.
5680N/A </p>
5680N/A<p>
5680N/A Using ACLs allows you to have finer control over who can access
5680N/A your name server, without cluttering up your config files with huge
220N/A lists of IP addresses.
220N/A </p>
5777N/A<p>
220N/A It is a <span class="emphasis"><em>good idea</em></span> to use ACLs, and to
220N/A control access to your server. Limiting access to your server by
220N/A outside parties can help prevent spoofing and DoS attacks against
220N/A your server.
220N/A </p>
220N/A<p>
220N/A Here is an example of how to properly apply ACLs:
220N/A </p>
1328N/A<pre class="programlisting">
5074N/A// Set up an ACL named "bogusnets" that will block RFC1918 space
220N/A// and some reserved space, which is commonly used in spoofing attacks.
220N/Aacl bogusnets {
220N/A 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;
220N/A 10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
220N/A};
220N/A// Set up an ACL called our-nets. Replace this with the real IP numbers.
220N/Aacl our-nets { x.x.x.x/24; x.x.x.x/21; };
220N/Aoptions {
220N/A ...
220N/A ...
220N/A allow-query { our-nets; };
220N/A allow-recursion { our-nets; };
220N/A ...
220N/A blackhole { bogusnets; };
220N/A ...
3817N/A};
3817N/Azone "example.com" {
3817N/A type master;
3817N/A file "m/example.com";
3817N/A allow-query { any; };
3817N/A};
3817N/A</pre>
5795N/A<p>
6062N/A This allows recursive queries of the server from the outside
6062N/A unless recursion has been previously disabled.
3817N/A </p>
3817N/A<p>
3817N/A For more information on how to use ACLs to protect your server,
3817N/A see the <span class="emphasis"><em>AUSCERT</em></span> advisory at:
3817N/A </p>
6062N/A<p>
<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>
</p>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="id2573062"></a><span><strong class="command">chroot</strong></span> and <span><strong class="command">setuid</strong></span></h2></div></div></div>
<p>
On UNIX servers, it is possible to run <span class="acronym">BIND</span> in a <span class="emphasis"><em>chrooted</em></span> environment
(<span><strong class="command">chroot()</strong></span>) by specifying the "<code class="option">-t</code>"
option. This can help improve system security by placing <span class="acronym">BIND</span> in
a "sandbox", which will limit the damage done if a server is
compromised.
</p>
<p>
Another useful feature in the UNIX version of <span class="acronym">BIND</span> is the
ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ).
We suggest running as an unprivileged user when using the <span><strong class="command">chroot</strong></span> feature.
</p>
<p>
Here is an example command line to load <span class="acronym">BIND</span> in a <span><strong class="command">chroot()</strong></span> sandbox,
<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
user 202:
</p>
<p>
<strong class="userinput"><code>/usr/local/bin/named -u 202 -t /var/named</code></strong>
</p>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573274"></a>The <span><strong class="command">chroot</strong></span> Environment</h3></div></div></div>
<p>
In order for a <span><strong class="command">chroot()</strong></span> environment
to
work properly in a particular directory
(for example, <code class="filename">/var/named</code>),
you will need to set up an environment that includes everything
<span class="acronym">BIND</span> needs to run.
From <span class="acronym">BIND</span>'s point of view, <code class="filename">/var/named</code> is
the root of the filesystem. You will need to adjust the values of
options like
like <span><strong class="command">directory</strong></span> and <span><strong class="command">pid-file</strong></span> to account
for this.
</p>
<p>
Unlike with earlier versions of BIND, you will typically
<span class="emphasis"><em>not</em></span> need to compile <span><strong class="command">named</strong></span>
statically nor install shared libraries under the new root.
However, depending on your operating system, you may need
to set up things like
<code class="filename">/dev/zero</code>,
<code class="filename">/dev/random</code>,
<code class="filename">/dev/log</code>, and/or
<code class="filename">/etc/localtime</code>.
</p>
</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2573402"></a>Using the <span><strong class="command">setuid</strong></span> Function</h3></div></div></div>
<p>
Prior to running the <span><strong class="command">named</strong></span> daemon,
use
the <span><strong class="command">touch</strong></span> utility (to change file
access and
modification times) or the <span><strong class="command">chown</strong></span>
utility (to
set the user id and/or group id) on files
to which you want <span class="acronym">BIND</span>
to write.
</p>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<h3 class="title">Note</h3>
Note that if the <span><strong class="command">named</strong></span> daemon is running as an
unprivileged user, it will not be able to bind to new restricted
ports if the server is reloaded.
</div>
</div>
</div>
<div class="sect1" lang="en">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="dynamic_update_security"></a>Dynamic Update Security</h2></div></div></div>
<p>
Access to the dynamic
update facility should be strictly limited. In earlier versions of
<span class="acronym">BIND</span> the only way to do this was
based on the IP
address of the host requesting the update, by listing an IP address
or
network prefix in the <span><strong class="command">allow-update</strong></span>
zone option.
This method is insecure since the source address of the update UDP
packet
is easily forged. Also note that if the IP addresses allowed by the
<span><strong class="command">allow-update</strong></span> option include the
address of a slave
server which performs forwarding of dynamic updates, the master can
be
trivially attacked by sending the update to the slave, which will
forward it to the master with its own source IP address causing the
master to approve it without question.
</p>
<p>
For these reasons, we strongly recommend that updates be
cryptographically authenticated by means of transaction signatures
(TSIG). That is, the <span><strong class="command">allow-update</strong></span>
option should
list only TSIG key names, not IP addresses or network
prefixes. Alternatively, the new <span><strong class="command">update-policy</strong></span>
option can be used.
</p>
<p>
Some sites choose to keep all dynamically updated DNS data
in a subdomain and delegate that subdomain to a separate zone. This
way, the top-level zone containing critical data such as the IP
addresses
of public web and mail servers need not allow dynamic update at
all.
</p>
</div>
</div>
<div class="navfooter">
<hr>
<table width="100%" summary="Navigation footer">
<tr>
<td width="40%" align="left">
<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td>
<td width="20%" align="center">�</td>
<td width="40%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
</td>
</tr>
<tr>
<td width="40%" align="left" valign="top">Chapter�6.�<span class="acronym">BIND</span> 9 Configuration Reference�</td>
<td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td>
<td width="40%" align="right" valign="top">�Chapter�8.�Troubleshooting</td>
</tr>
</table>
</div>
</body>
</html>