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

   1 <!--
   2  - Copyright (C) 2004-2010 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: Bv9ARM.ch07.html,v 1.178.14.13.2.1 2010/02/25 12:16:47 tbox Exp $ -->
  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#id2599054"><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#id2599136">The <span><strong class="command">chroot</strong></span> Environment</a></span></dt>
  52 <dt><span class="sect2"><a href="Bv9ARM.ch07.html#id2599264">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 RFC1918 space
  84 // and some reserved space, which is commonly used in spoofing attacks.
  85 acl bogusnets {
  86         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;
  87         10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
  88 };
  89
  90 // Set up an ACL called our-nets. Replace this with the real IP numbers.
  91 acl our-nets { x.x.x.x/24; x.x.x.x/21; };
  92 options {
  93   ...
  94   ...
  95   allow-query { our-nets; };
  96   allow-recursion { our-nets; };
  97   ...
  98   blackhole { bogusnets; };
  99   ...
 100 };
 101
 102 zone "example.com" {
 103   type master;
 104   file "m/example.com";
 105   allow-query { any; };
 106 };
 107 </pre>
 108 <p>
 109           This allows recursive queries of the server from the outside
 110           unless recursion has been previously disabled.
 111         </p>
 112 <p>
 113           For more information on how to use ACLs to protect your server,
 114           see the <span class="emphasis"><em>AUSCERT</em></span> advisory at:
 115         </p>
 116 <p>
 117           <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>
 118         </p>
 119 </div>
 120 <div class="sect1" lang="en">
 121 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 122 <a name="id2599054"></a><span><strong class="command">Chroot</strong></span> and <span><strong class="command">Setuid</strong></span>
 123 </h2></div></div></div>
 124 <p>
 125           On UNIX servers, it is possible to run <acronym class="acronym">BIND</acronym>
 126           in a <span class="emphasis"><em>chrooted</em></span> environment (using
 127           the <span><strong class="command">chroot()</strong></span> function) by specifying
 128           the "<code class="option">-t</code>" option for <span><strong class="command">named</strong></span>.
 129           This can help improve system security by placing
 130           <acronym class="acronym">BIND</acronym> in a "sandbox", which will limit
 131           the damage done if a server is compromised.
 132         </p>
 133 <p>
 134           Another useful feature in the UNIX version of <acronym class="acronym">BIND</acronym> is the
 135           ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ).
 136           We suggest running as an unprivileged user when using the <span><strong class="command">chroot</strong></span> feature.
 137         </p>
 138 <p>
 139           Here is an example command line to load <acronym class="acronym">BIND</acronym> in a <span><strong class="command">chroot</strong></span> sandbox,
 140           <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
 141           user 202:
 142         </p>
 143 <p>
 144           <strong class="userinput"><code>/usr/local/sbin/named -u 202 -t /var/named</code></strong>
 145         </p>
 146 <div class="sect2" lang="en">
 147 <div class="titlepage"><div><div><h3 class="title">
 148 <a name="id2599136"></a>The <span><strong class="command">chroot</strong></span> Environment</h3></div></div></div>
 149 <p>
 150             In order for a <span><strong class="command">chroot</strong></span> environment
 151             to
 152             work properly in a particular directory
 153             (for example, <code class="filename">/var/named</code>),
 154             you will need to set up an environment that includes everything
 155             <acronym class="acronym">BIND</acronym> needs to run.
 156             From <acronym class="acronym">BIND</acronym>'s point of view, <code class="filename">/var/named</code> is
 157             the root of the filesystem.  You will need to adjust the values of
 158             options like
 159             like <span><strong class="command">directory</strong></span> and <span><strong class="command">pid-file</strong></span> to account
 160             for this.
 161           </p>
 162 <p>
 163             Unlike with earlier versions of BIND, you typically will
 164             <span class="emphasis"><em>not</em></span> need to compile <span><strong class="command">named</strong></span>
 165             statically nor install shared libraries under the new root.
 166             However, depending on your operating system, you may need
 167             to set up things like
 168             <code class="filename">/dev/zero</code>,
 169             <code class="filename">/dev/random</code>,
 170             <code class="filename">/dev/log</code>, and
 171             <code class="filename">/etc/localtime</code>.
 172           </p>
 173 </div>
 174 <div class="sect2" lang="en">
 175 <div class="titlepage"><div><div><h3 class="title">
 176 <a name="id2599264"></a>Using the <span><strong class="command">setuid</strong></span> Function</h3></div></div></div>
 177 <p>
 178             Prior to running the <span><strong class="command">named</strong></span> daemon,
 179             use
 180             the <span><strong class="command">touch</strong></span> utility (to change file
 181             access and
 182             modification times) or the <span><strong class="command">chown</strong></span>
 183             utility (to
 184             set the user id and/or group id) on files
 185             to which you want <acronym class="acronym">BIND</acronym>
 186             to write.
 187           </p>
 188 <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
 189 <h3 class="title">Note</h3>
 190             Note that if the <span><strong class="command">named</strong></span> daemon is running as an
 191             unprivileged user, it will not be able to bind to new restricted
 192             ports if the server is reloaded.
 193           </div>
 194 </div>
 195 </div>
 196 <div class="sect1" lang="en">
 197 <div class="titlepage"><div><div><h2 class="title" style="clear: both">
 198 <a name="dynamic_update_security"></a>Dynamic Update Security</h2></div></div></div>
 199 <p>
 200           Access to the dynamic
 201           update facility should be strictly limited.  In earlier versions of
 202           <acronym class="acronym">BIND</acronym>, the only way to do this was
 203           based on the IP
 204           address of the host requesting the update, by listing an IP address
 205           or
 206           network prefix in the <span><strong class="command">allow-update</strong></span>
 207           zone option.
 208           This method is insecure since the source address of the update UDP
 209           packet
 210           is easily forged.  Also note that if the IP addresses allowed by the
 211           <span><strong class="command">allow-update</strong></span> option include the
 212           address of a slave
 213           server which performs forwarding of dynamic updates, the master can
 214           be
 215           trivially attacked by sending the update to the slave, which will
 216           forward it to the master with its own source IP address causing the
 217           master to approve it without question.
 218         </p>
 219 <p>
 220           For these reasons, we strongly recommend that updates be
 221           cryptographically authenticated by means of transaction signatures
 222           (TSIG).  That is, the <span><strong class="command">allow-update</strong></span>
 223           option should
 224           list only TSIG key names, not IP addresses or network
 225           prefixes. Alternatively, the new <span><strong class="command">update-policy</strong></span>
 226           option can be used.
 227         </p>
 228 <p>
 229           Some sites choose to keep all dynamically-updated DNS data
 230           in a subdomain and delegate that subdomain to a separate zone. This
 231           way, the top-level zone containing critical data such as the IP
 232           addresses
 233           of public web and mail servers need not allow dynamic update at
 234           all.
 235         </p>
 236 </div>
 237 </div>
 238 <div class="navfooter">
 239 <hr>
 240 <table width="100%" summary="Navigation footer">
 241 <tr>
 242 <td width="40%" align="left">
 243 <a accesskey="p" href="Bv9ARM.ch06.html">Prev</a> </td>
 244 <td width="20%" align="center"> </td>
 245 <td width="40%" align="right"> <a accesskey="n" href="Bv9ARM.ch08.html">Next</a>
 246 </td>
 247 </tr>
 248 <tr>
 249 <td width="40%" align="left" valign="top">Chapter 6. <acronym class="acronym">BIND</acronym> 9 Configuration Reference </td>
 250 <td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td>
 251 <td width="40%" align="right" valign="top"> Chapter 8. Troubleshooting</td>
 252 </tr>
 253 </table>
 254 </div>
 255 </body>
 256 </html>