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5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<title>Chapter�7.�BIND 9 Security Considerations</title>
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5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<link rel="next" href="Bv9ARM.ch08.html" title="Chapter�8.�Troubleshooting">
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a84724de8db9e52857fb11bbcdb195658f9a05b2Michael Graff<table width="100%" summary="Navigation header">
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<tr><th colspan="3" align="center">Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</th></tr>
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5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<hr>
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5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<div class="chapter" lang="en">
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<div class="titlepage"><div><div><h2 class="title">
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<a name="Bv9ARM.ch07"></a>Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</h2></div></div></div>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<div class="toc">
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<p><b>Table of Contents</b></p>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dl>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dt><span class="sect1"><a href="Bv9ARM.ch07.html#Access_Control_Lists">Access Control Lists</a></span></dt>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dt><span class="sect1"><a href="Bv9ARM.ch07.html#id2599921"><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span></a></span></dt>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dd><dl>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2600070">The <span><strong class="command">chroot</strong></span> Environment</a></span></dt>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2600130">Using the <span><strong class="command">setuid</strong></span> Function</a></span></dt>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉</dl></dd>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<dt><span class="sect1"><a href="Bv9ARM.ch07.html#dynamic_update_security">Dynamic Update Security</a></span></dt>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉</dl>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉</div>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<div class="sect1" lang="en">
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<div class="titlepage"><div><div><h2 class="title" style="clear: both">
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<a name="Access_Control_Lists"></a>Access Control Lists</h2></div></div></div>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉<p>
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉 Access Control Lists (ACLs) are address match lists that
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉 you can set up and nickname for future use in <span><strong class="command">allow-notify</strong></span>,
1c3ed2a83d176d9023b51b60dfc96c133f678362Tatuya JINMEI 神明達哉 <span><strong class="command">allow-query</strong></span>, <span><strong class="command">allow-query-on</strong></span>,
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 <span><strong class="command">allow-recursion</strong></span>, <span><strong class="command">allow-recursion-on</strong></span>,
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 <span><strong class="command">blackhole</strong></span>, <span><strong class="command">allow-transfer</strong></span>,
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 etc.
a84724de8db9e52857fb11bbcdb195658f9a05b2Michael Graff </p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 Using ACLs allows you to have finer control over who can access
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 your name server, without cluttering up your config files with huge
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 lists of IP addresses.
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 </p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 It is a <span class="emphasis"><em>good idea</em></span> to use ACLs, and to
cbf0854acc9f5d11142dba30b1ab23e0532baaf2Automatic Updater control access to your server. Limiting access to your server by
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 outside parties can help prevent spoofing and denial of service (DoS) attacks against
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 your server.
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 </p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 Here is an example of how to properly apply ACLs:
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 </p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉<pre class="programlisting">
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉// Set up an ACL named "bogusnets" that will block
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉// RFC1918 space and some reserved space, which is
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉// commonly used in spoofing attacks.
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉acl bogusnets {
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 0.0.0.0/8; 1.0.0.0/8; 2.0.0.0/8; 192.0.2.0/24;
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 224.0.0.0/3; 10.0.0.0/8; 172.16.0.0/12;
a84724de8db9e52857fb11bbcdb195658f9a05b2Michael Graff 192.168.0.0/16;
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉};
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉// Set up an ACL called our-nets. Replace this with the
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉// real IP numbers.
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉acl our-nets { x.x.x.x/24; x.x.x.x/21; };
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉options {
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 ...
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 ...
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 allow-query { our-nets; };
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 allow-recursion { our-nets; };
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 ...
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 blackhole { bogusnets; };
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉 ...
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉};
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉zone "example.com" {
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 type master;
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 file "m/example.com";
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 allow-query { any; };
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉};
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉</pre>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 This allows recursive queries of the server from the outside
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 unless recursion has been previously disabled.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 For more information on how to use ACLs to protect your server,
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 see the <span class="emphasis"><em>AUSCERT</em></span> advisory at:
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <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>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉</div>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<div class="sect1" lang="en">
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<div class="titlepage"><div><div><h2 class="title" style="clear: both">
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<a name="id2599921"></a><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉</h2></div></div></div>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 On UNIX servers, it is possible to run <acronym class="acronym">BIND</acronym>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 in a <span class="emphasis"><em>chrooted</em></span> environment (using
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 the <span><strong class="command">chroot()</strong></span> function) by specifying
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 the "<code class="option">-t</code>" option for <span><strong class="command">named</strong></span>.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 This can help improve system security by placing
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <acronym class="acronym">BIND</acronym> in a "sandbox", which will limit
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 the damage done if a server is compromised.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 Another useful feature in the UNIX version of <acronym class="acronym">BIND</acronym> is the
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ).
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 We suggest running as an unprivileged user when using the <span><strong class="command">chroot</strong></span> feature.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 Here is an example command line to load <acronym class="acronym">BIND</acronym> in a <span><strong class="command">chroot</strong></span> sandbox,
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <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
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 user 202:
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <strong class="userinput"><code>/usr/local/sbin/named -u 202 -t /var/named</code></strong>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<div class="sect2" lang="en">
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<div class="titlepage"><div><div><h3 class="title">
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<a name="id2600070"></a>The <span><strong class="command">chroot</strong></span> Environment</h3></div></div></div>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 In order for a <span><strong class="command">chroot</strong></span> environment
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 to
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 work properly in a particular directory
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 (for example, <code class="filename">/var/named</code>),
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 you will need to set up an environment that includes everything
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <acronym class="acronym">BIND</acronym> needs to run.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 From <acronym class="acronym">BIND</acronym>'s point of view, <code class="filename">/var/named</code> is
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 the root of the filesystem. You will need to adjust the values of
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 options like
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 like <span><strong class="command">directory</strong></span> and <span><strong class="command">pid-file</strong></span> to account
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 for this.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉<p>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 Unlike with earlier versions of BIND, you typically will
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <span class="emphasis"><em>not</em></span> need to compile <span><strong class="command">named</strong></span>
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 statically nor install shared libraries under the new root.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 However, depending on your operating system, you may need
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 to set up things like
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <code class="filename">/dev/zero</code>,
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <code class="filename">/dev/random</code>,
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <code class="filename">/dev/log</code>, and
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 <code class="filename">/etc/localtime</code>.
c528bd698637d84a0081d26a58813607c7f52bb7Tatuya JINMEI 神明達哉 </p>
5597be9bb88de138dfec9fa9176708443813925eTatuya JINMEI 神明達哉</div>
<div class="sect2" lang="en">
<div class="titlepage"><div><div><h3 class="title">
<a name="id2600130"></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 <acronym class="acronym">BIND</acronym>
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
<acronym class="acronym">BIND</acronym>, 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>
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