contrib/bind9/doc/arm/Bv9ARM.ch07.html

   1 <!--
   2  - Copyright (C) 2004-2012 Internet Systems Consortium, Inc. ("ISC")
   3  - Copyright (C) 2000-2003 Internet Software Consortium.
   4  -
   5  - Permission to use, copy, modify, and/or distribute this software for any
   6  - purpose with or without fee is hereby granted, provided that the above
   7  - copyright notice and this permission notice appear in all copies.
   8  -
   9  - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
  10  - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
  11  - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
  12  - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
  13  - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
  14  - OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
  15  - PERFORMANCE OF THIS SOFTWARE.
  16 -->
  17 <!-- $Id$ -->
  18 <html>
  19 <head>
  20 <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
  21 <title>Chapter 7. BIND 9 Security Considerations</title>
  22 <meta name="generator" content="DocBook XSL Stylesheets V1.71.1">
  23 <link rel="start" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
  24 <link rel="up" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual">
  25 <link rel="prev" href="Bv9ARM.ch06.html" title="Chapter 6. BIND 9 Configuration Reference">
  26 <link rel="next" href="Bv9ARM.ch08.html" title="Chapter 8. Troubleshooting">
  27 </head>
  28 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  29 <div class="navheader">
  30 <table width="100%" summary="Navigation header">
  31 <tr><th colspan="3" align="center">Chapter 7. <acronym class="acronym">BIND</acronym> 9 Security Considerations</th></tr>
  32 <tr>
  33 <td width="20%" align="left">
  34 <a accesskey="p" href="Bv9ARM.ch06.html">Prev</a> </td>
  35 <th width="60%" align="center"> </th>
  36 <td width="20%" align="right"> <a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
  37 </td>
  38 </tr>
  39 </table>
  40 <hr>
  41 </div>
  42 <div class="chapter" lang="en">
  43 <div class="titlepage"><div><div><h2 class="title">
  44 <a name="Bv9ARM.ch07"></a>Chapter 7. <acronym class="acronym">BIND</acronym> 9 Security Considerations</h2></div></div></div>
  45 <div class="toc">
  46 <p><b>Table of Contents</b></p>
  47 <dl>
  48 <dt><span class="sect1"><a href="Bv9ARM.ch07.html#Access_Control_Lists">Access Control Lists</a></span></dt>
  49 <dt><span class="sect1"><a href="Bv9ARM.ch07.html#id2603136"><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span></a></span></dt>
  50 <dd><dl>
  51 <dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2603285">The <span><strong class="command">chroot</strong></span> Environment</a></span></dt>
  52 <dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2603345">Using the <span><strong class="command">setuid</strong></span> Function</a></span></dt>
  53 </dl></dd>
  54 <dt><span class="sect1"><a href="Bv9ARM.ch07.html#dynamic_update_security">Dynamic Update Security</a></span></dt>
  55 </dl>
  56 </div>
  57 <div class="sect1" lang="en">
  58 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
  59 <a name="Access_Control_Lists"></a>Access Control Lists</h2></div></div></div>
  60 <p>
  61           Access Control Lists (ACLs) are address match lists that
  62           you can set up and nickname for future use in <span><strong class="command">allow-notify</strong></span>,
  63           <span><strong class="command">allow-query</strong></span>, <span><strong class="command">allow-query-on</strong></span>,
  64           <span><strong class="command">allow-recursion</strong></span>, <span><strong class="command">allow-recursion-on</strong></span>,
  65           <span><strong class="command">blackhole</strong></span>, <span><strong class="command">allow-transfer</strong></span>,
  66           etc.
  67         </p>
  68 <p>
  69           Using ACLs allows you to have finer control over who can access
  70           your name server, without cluttering up your config files with huge
  71           lists of IP addresses.
  72         </p>
  73 <p>
  74           It is a <span class="emphasis"><em>good idea</em></span> to use ACLs, and to
  75           control access to your server. Limiting access to your server by
  76           outside parties can help prevent spoofing and denial of service (DoS) attacks against
  77           your server.
  78         </p>
  79 <p>
  80           Here is an example of how to properly apply ACLs:
  81         </p>
  82 <pre class="programlisting">
  83 // Set up an ACL named "bogusnets" that will block
  84 // RFC1918 space and some reserved space, which is
  85 // commonly used in spoofing attacks.
  86 acl bogusnets {
  87         0.0.0.0/8;  192.0.2.0/24; 224.0.0.0/3;
  88         10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
  89 };
  90
  91 // Set up an ACL called our-nets. Replace this with the
  92 // real IP numbers.
  93 acl our-nets { x.x.x.x/24; x.x.x.x/21; };
  94 options {
  95   ...
  96   ...
  97   allow-query { our-nets; };
  98   allow-recursion { our-nets; };
  99   ...
 100   blackhole { bogusnets; };
 101   ...
 102 };
 103
 104 zone "example.com" {
 105   type master;
 106   file "m/example.com";
 107   allow-query { any; };
 108 };
 109 </pre>
 110 <p>
 111           This allows recursive queries of the server from the outside
 112           unless recursion has been previously disabled.
 113         </p>
 114 <p>
 115           For more information on how to use ACLs to protect your server,
 116           see the <span class="emphasis"><em>AUSCERT</em></span> advisory at:
 117         </p>
 118 <p>
 119           <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>
 120         </p>
 121 </div>
 122 <div class="sect1" lang="en">
 123 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 124 <a name="id2603136"></a><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span>
 125 </h2></div></div></div>
 126 <p>
 127           On UNIX servers, it is possible to run <acronym class="acronym">BIND</acronym>
 128           in a <span class="emphasis"><em>chrooted</em></span> environment (using
 129           the <span><strong class="command">chroot()</strong></span> function) by specifying
 130           the "<code class="option">-t</code>" option for <span><strong class="command">named</strong></span>.
 131           This can help improve system security by placing
 132           <acronym class="acronym">BIND</acronym> in a "sandbox", which will limit
 133           the damage done if a server is compromised.
 134         </p>
 135 <p>
 136           Another useful feature in the UNIX version of <acronym class="acronym">BIND</acronym> is the
 137           ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ).
 138           We suggest running as an unprivileged user when using the <span><strong class="command">chroot</strong></span> feature.
 139         </p>
 140 <p>
 141           Here is an example command line to load <acronym class="acronym">BIND</acronym> in a <span><strong class="command">chroot</strong></span> sandbox,
 142           <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
 143           user 202:
 144         </p>
 145 <p>
 146           <strong class="userinput"><code>/usr/local/sbin/named -u 202 -t /var/named</code></strong>
 147         </p>
 148 <div class="sect2" lang="en">
 149 <div class="titlepage"><div><div><h3 class="title">
 150 <a name="id2603285"></a>The <span><strong class="command">chroot</strong></span> Environment</h3></div></div></div>
 151 <p>
 152             In order for a <span><strong class="command">chroot</strong></span> environment
 153             to
 154             work properly in a particular directory
 155             (for example, <code class="filename">/var/named</code>),
 156             you will need to set up an environment that includes everything
 157             <acronym class="acronym">BIND</acronym> needs to run.
 158             From <acronym class="acronym">BIND</acronym>'s point of view, <code class="filename">/var/named</code> is
 159             the root of the filesystem.  You will need to adjust the values of
 160             options like
 161             like <span><strong class="command">directory</strong></span> and <span><strong class="command">pid-file</strong></span> to account
 162             for this.
 163           </p>
 164 <p>
 165             Unlike with earlier versions of BIND, you typically will
 166             <span class="emphasis"><em>not</em></span> need to compile <span><strong class="command">named</strong></span>
 167             statically nor install shared libraries under the new root.
 168             However, depending on your operating system, you may need
 169             to set up things like
 170             <code class="filename">/dev/zero</code>,
 171             <code class="filename">/dev/random</code>,
 172             <code class="filename">/dev/log</code>, and
 173             <code class="filename">/etc/localtime</code>.
 174           </p>
 175 </div>
 176 <div class="sect2" lang="en">
 177 <div class="titlepage"><div><div><h3 class="title">
 178 <a name="id2603345"></a>Using the <span><strong class="command">setuid</strong></span> Function</h3></div></div></div>
 179 <p>
 180             Prior to running the <span><strong class="command">named</strong></span> daemon,
 181             use
 182             the <span><strong class="command">touch</strong></span> utility (to change file
 183             access and
 184             modification times) or the <span><strong class="command">chown</strong></span>
 185             utility (to
 186             set the user id and/or group id) on files
 187             to which you want <acronym class="acronym">BIND</acronym>
 188             to write.
 189           </p>
 190 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
 191 <h3 class="title">Note</h3>
 192             Note that if the <span><strong class="command">named</strong></span> daemon is running as an
 193             unprivileged user, it will not be able to bind to new restricted
 194             ports if the server is reloaded.
 195           </div>
 196 </div>
 197 </div>
 198 <div class="sect1" lang="en">
 199 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 200 <a name="dynamic_update_security"></a>Dynamic Update Security</h2></div></div></div>
 201 <p>
 202           Access to the dynamic
 203           update facility should be strictly limited.  In earlier versions of
 204           <acronym class="acronym">BIND</acronym>, the only way to do this was
 205           based on the IP
 206           address of the host requesting the update, by listing an IP address
 207           or
 208           network prefix in the <span><strong class="command">allow-update</strong></span>
 209           zone option.
 210           This method is insecure since the source address of the update UDP
 211           packet
 212           is easily forged.  Also note that if the IP addresses allowed by the
 213           <span><strong class="command">allow-update</strong></span> option include the
 214           address of a slave
 215           server which performs forwarding of dynamic updates, the master can
 216           be
 217           trivially attacked by sending the update to the slave, which will
 218           forward it to the master with its own source IP address causing the
 219           master to approve it without question.
 220         </p>
 221 <p>
 222           For these reasons, we strongly recommend that updates be
 223           cryptographically authenticated by means of transaction signatures
 224           (TSIG).  That is, the <span><strong class="command">allow-update</strong></span>
 225           option should
 226           list only TSIG key names, not IP addresses or network
 227           prefixes. Alternatively, the new <span><strong class="command">update-policy</strong></span>
 228           option can be used.
 229         </p>
 230 <p>
 231           Some sites choose to keep all dynamically-updated DNS data
 232           in a subdomain and delegate that subdomain to a separate zone. This
 233           way, the top-level zone containing critical data such as the IP
 234           addresses
 235           of public web and mail servers need not allow dynamic update at
 236           all.
 237         </p>
 238 </div>
 239 </div>
 240 <div class="navfooter">
 241 <hr>
 242 <table width="100%" summary="Navigation footer">
 243 <tr>
 244 <td width="40%" align="left">
 245 <a accesskey="p" href="Bv9ARM.ch06.html">Prev</a> </td>
 246 <td width="20%" align="center"> </td>
 247 <td width="40%" align="right"> <a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
 248 </td>
 249 </tr>
 250 <tr>
 251 <td width="40%" align="left" valign="top">Chapter 6. <acronym class="acronym">BIND</acronym> 9 Configuration Reference </td>
 252 <td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td>
 253 <td width="40%" align="right" valign="top"> Chapter 8. Troubleshooting</td>
 254 </tr>
 255 </table>
 256 </div>
 257 </body>
 258 </html>