1<!-- 2 - Copyright (C) 2004-2015 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<html> 18<head> 19<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> 20<title>Chapter�7.�BIND 9 Security Considerations</title> 21<meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> 22<link rel="home" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual"> 23<link rel="up" href="Bv9ARM.html" title="BIND 9 Administrator Reference Manual"> 24<link rel="prev" href="Bv9ARM.ch06.html" title="Chapter�6.�BIND 9 Configuration Reference"> 25<link rel="next" href="Bv9ARM.ch08.html" title="Chapter�8.�Troubleshooting"> 26</head> 27<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 28<div class="navheader"> 29<table width="100%" summary="Navigation header"> 30<tr><th colspan="3" align="center">Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</th></tr> 31<tr> 32<td width="20%" align="left"> 33<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td> 34<th width="60%" align="center">�</th> 35<td width="20%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a> 36</td> 37</tr> 38</table> 39<hr> 40</div> 41<div class="chapter"> 42<div class="titlepage"><div><div><h1 class="title"> 43<a name="Bv9ARM.ch07"></a>Chapter�7.�<acronym class="acronym">BIND</acronym> 9 Security Considerations</h1></div></div></div> 44<div class="toc"> 45<p><b>Table of Contents</b></p> 46<dl class="toc"> 47<dt><span class="section"><a href="Bv9ARM.ch07.html#Access_Control_Lists">Access Control Lists</a></span></dt> 48<dt><span class="section"><a href="Bv9ARM.ch07.html#chroot_and_setuid"><span class="command"><strong>Chroot</strong></span> and <span class="command"><strong>Setuid</strong></span></a></span></dt> 49<dd><dl> 50<dt><span class="section"><a href="Bv9ARM.ch07.html#chroot">The <span class="command"><strong>chroot</strong></span> Environment</a></span></dt> 51<dt><span class="section"><a href="Bv9ARM.ch07.html#setuid">Using the <span class="command"><strong>setuid</strong></span> Function</a></span></dt> 52</dl></dd> 53<dt><span class="section"><a href="Bv9ARM.ch07.html#dynamic_update_security">Dynamic Update Security</a></span></dt> 54</dl> 55</div> 56<div class="section"> 57<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 58<a name="Access_Control_Lists"></a>Access Control Lists</h2></div></div></div> 59<p> 60 Access Control Lists (ACLs) are address match lists that 61 you can set up and nickname for future use in <span class="command"><strong>allow-notify</strong></span>, 62 <span class="command"><strong>allow-query</strong></span>, <span class="command"><strong>allow-query-on</strong></span>, 63 <span class="command"><strong>allow-recursion</strong></span>, <span class="command"><strong>allow-recursion-on</strong></span>, 64 <span class="command"><strong>blackhole</strong></span>, <span class="command"><strong>allow-transfer</strong></span>, 65 etc. 66 </p> 67<p> 68 Using ACLs allows you to have finer control over who can access 69 your name server, without cluttering up your config files with huge 70 lists of IP addresses. 71 </p> 72<p> 73 It is a <span class="emphasis"><em>good idea</em></span> to use ACLs, and to 74 control access to your server. Limiting access to your server by 75 outside parties can help prevent spoofing and denial of service (DoS) attacks against 76 your server. 77 </p> 78<p> 79 Here is an example of how to properly apply ACLs: 80 </p> 81<pre class="programlisting"> 82// Set up an ACL named "bogusnets" that will block 83// RFC1918 space and some reserved space, which is 84// commonly used in spoofing attacks. 85acl bogusnets { 86 0.0.0.0/8; 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 91// real IP numbers. 92acl our-nets { x.x.x.x/24; x.x.x.x/21; }; 93options { 94 ... 95 ... 96 allow-query { our-nets; }; 97 allow-recursion { our-nets; }; 98 ... 99 blackhole { bogusnets; }; 100 ... 101}; 102 103zone "example.com" { 104 type master; 105 file "m/example.com"; 106 allow-query { any; }; 107}; 108</pre> 109<p> 110 This allows recursive queries of the server from the outside 111 unless recursion has been previously disabled. 112 </p> 113</div> 114<div class="section"> 115<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 116<a name="chroot_and_setuid"></a><span class="command"><strong>Chroot</strong></span> and <span class="command"><strong>Setuid</strong></span> 117</h2></div></div></div> 118<p> 119 On UNIX servers, it is possible to run <acronym class="acronym">BIND</acronym> 120 in a <span class="emphasis"><em>chrooted</em></span> environment (using 121 the <span class="command"><strong>chroot()</strong></span> function) by specifying 122 the "<code class="option">-t</code>" option for <span class="command"><strong>named</strong></span>. 123 This can help improve system security by placing 124 <acronym class="acronym">BIND</acronym> in a "sandbox", which will limit 125 the damage done if a server is compromised. 126 </p> 127<p> 128 Another useful feature in the UNIX version of <acronym class="acronym">BIND</acronym> is the 129 ability to run the daemon as an unprivileged user ( <code class="option">-u</code> <em class="replaceable"><code>user</code></em> ). 130 We suggest running as an unprivileged user when using the <span class="command"><strong>chroot</strong></span> feature. 131 </p> 132<p> 133 Here is an example command line to load <acronym class="acronym">BIND</acronym> in a <span class="command"><strong>chroot</strong></span> sandbox, 134 <span class="command"><strong>/var/named</strong></span>, and to run <span class="command"><strong>named</strong></span> <span class="command"><strong>setuid</strong></span> to 135 user 202: 136 </p> 137<p> 138 <strong class="userinput"><code>/usr/local/sbin/named -u 202 -t /var/named</code></strong> 139 </p> 140<div class="section"> 141<div class="titlepage"><div><div><h3 class="title"> 142<a name="chroot"></a>The <span class="command"><strong>chroot</strong></span> Environment</h3></div></div></div> 143<p> 144 In order for a <span class="command"><strong>chroot</strong></span> environment 145 to 146 work properly in a particular directory 147 (for example, <code class="filename">/var/named</code>), 148 you will need to set up an environment that includes everything 149 <acronym class="acronym">BIND</acronym> needs to run. 150 From <acronym class="acronym">BIND</acronym>'s point of view, <code class="filename">/var/named</code> is 151 the root of the filesystem. You will need to adjust the values of 152 options like 153 like <span class="command"><strong>directory</strong></span> and <span class="command"><strong>pid-file</strong></span> to account 154 for this. 155 </p> 156<p> 157 Unlike with earlier versions of BIND, you typically will 158 <span class="emphasis"><em>not</em></span> need to compile <span class="command"><strong>named</strong></span> 159 statically nor install shared libraries under the new root. 160 However, depending on your operating system, you may need 161 to set up things like 162 <code class="filename">/dev/zero</code>, 163 <code class="filename">/dev/random</code>, 164 <code class="filename">/dev/log</code>, and 165 <code class="filename">/etc/localtime</code>. 166 </p> 167</div> 168<div class="section"> 169<div class="titlepage"><div><div><h3 class="title"> 170<a name="setuid"></a>Using the <span class="command"><strong>setuid</strong></span> Function</h3></div></div></div> 171<p> 172 Prior to running the <span class="command"><strong>named</strong></span> daemon, 173 use 174 the <span class="command"><strong>touch</strong></span> utility (to change file 175 access and 176 modification times) or the <span class="command"><strong>chown</strong></span> 177 utility (to 178 set the user id and/or group id) on files 179 to which you want <acronym class="acronym">BIND</acronym> 180 to write. 181 </p> 182<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> 183<h3 class="title">Note</h3> 184<p> 185 If the <span class="command"><strong>named</strong></span> daemon is running as an 186 unprivileged user, it will not be able to bind to new restricted 187 ports if the server is reloaded. 188 </p> 189</div> 190</div> 191</div> 192<div class="section"> 193<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 194<a name="dynamic_update_security"></a>Dynamic Update Security</h2></div></div></div> 195<p> 196 Access to the dynamic 197 update facility should be strictly limited. In earlier versions of 198 <acronym class="acronym">BIND</acronym>, the only way to do this was 199 based on the IP 200 address of the host requesting the update, by listing an IP address 201 or 202 network prefix in the <span class="command"><strong>allow-update</strong></span> 203 zone option. 204 This method is insecure since the source address of the update UDP 205 packet 206 is easily forged. Also note that if the IP addresses allowed by the 207 <span class="command"><strong>allow-update</strong></span> option include the 208 address of a slave 209 server which performs forwarding of dynamic updates, the master can 210 be 211 trivially attacked by sending the update to the slave, which will 212 forward it to the master with its own source IP address causing the 213 master to approve it without question. 214 </p> 215<p> 216 For these reasons, we strongly recommend that updates be 217 cryptographically authenticated by means of transaction signatures 218 (TSIG). That is, the <span class="command"><strong>allow-update</strong></span> 219 option should 220 list only TSIG key names, not IP addresses or network 221 prefixes. Alternatively, the new <span class="command"><strong>update-policy</strong></span> 222 option can be used. 223 </p> 224<p> 225 Some sites choose to keep all dynamically-updated DNS data 226 in a subdomain and delegate that subdomain to a separate zone. This 227 way, the top-level zone containing critical data such as the IP 228 addresses 229 of public web and mail servers need not allow dynamic update at 230 all. 231 </p> 232</div> 233</div> 234<div class="navfooter"> 235<hr> 236<table width="100%" summary="Navigation footer"> 237<tr> 238<td width="40%" align="left"> 239<a accesskey="p" href="Bv9ARM.ch06.html">Prev</a>�</td> 240<td width="20%" align="center">�</td> 241<td width="40%" align="right">�<a accesskey="n" href="Bv9ARM.ch08.html">Next</a> 242</td> 243</tr> 244<tr> 245<td width="40%" align="left" valign="top">Chapter�6.�<acronym class="acronym">BIND</acronym> 9 Configuration Reference�</td> 246<td width="20%" align="center"><a accesskey="h" href="Bv9ARM.html">Home</a></td> 247<td width="40%" align="right" valign="top">�Chapter�8.�Troubleshooting</td> 248</tr> 249</table> 250</div> 251<p xmlns:db="http://docbook.org/ns/docbook" style="text-align: center;">BIND 9.9.9-P4 (Extended Support Version)</p> 252</body> 253</html> 254