<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd"> <article> <!--$Id$--> <articleinfo> <title>Shorewall Blacklisting/Whitelisting Support</title> <authorgroup> <author> <firstname>Tom</firstname> <surname>Eastep</surname> </author> </authorgroup> <pubdate><?dbtimestamp format="Y/m/d"?></pubdate> <copyright> <year>2002-2006</year> <year>2010</year> <year>2011</year> <holder>Thomas M. Eastep</holder> </copyright> <legalnotice> <para>Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled <quote><ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para> </legalnotice> </articleinfo> <caution> <para><emphasis role="bold">This article applies to Shorewall 4.4 and later. If you are running a version of Shorewall earlier than Shorewall 4.3.5 then please see the documentation for that release.</emphasis></para> </caution> <section id="Intro"> <title>Introduction</title> <para>Shorewall supports two different types of blackliisting; rule-based, static and dynamic. The BLACKLISTNEWONLY option in /etc/shorewall/shorewall.conf controls the degree of blacklist filtering:</para> <orderedlist> <listitem> <para>BLACKLISTNEWONLY=No -- All incoming packets are checked against the blacklist. New blacklist entries can be used to terminate existing connections.</para> </listitem> <listitem> <para>BLACKLISTNEWONLY=Yes -- The blacklists are only consulted for new connection requests. Blacklists may not be used to terminate existing connections.</para> </listitem> </orderedlist> </section> <section> <title>Rule-based Blacklisting</title> <para>Beginning with Shorewall 4.4.25, the preferred method of blacklisting and whitelisting is to use the blrules file (<ulink url="manpages/shorewall-blrules.html">shorewall-blrules</ulink> (5)). There you have access to the DROP, ACCEPT, REJECT and WHITELIST actions, standard and custom macros as well as standard and custom actions. See <ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5) for details.</para> <para>Example:</para> <programlisting>#ACTION SOURCE DEST PROTO DEST # PORTS(S) SECTION BLACKLIST WHITELIST net:70.90.191.126 all DROP net all udp 1023:1033,1434,5948,23773 DROP all net udp 1023:1033 DROP net all tcp 57,1433,1434,2401,2745,3127,3306,3410,4899,5554,5948,6101,8081,9898,23773 DROP net:221.192.199.48 all DROP net:61.158.162.9 all DROP net:81.21.54.100 all tcp 25 DROP net:84.108.168.139 all DROP net:200.55.14.18 all </programlisting> <para>Beginning with Shorewall 4.4.26, the <command>update</command> command supports a <option>-b</option> option that causes your legacy blacklisting configuration to use the blrules file.</para> <note> <para>If you prefer to keep your blacklisting rules in your rules file (<ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5)), you can place them in the BLACKLIST section of that file rather than in blrules.</para> </note> </section> <section> <title>Legacy Blacklisting</title> <para>Prior to 4.4.25, two forms of blacklisting were supported; static and dynamic. The dynamic variety is still appropriate for <firstterm>on-the-fly</firstterm> blacklisting; the static form is deprecated.</para> <important> <para><emphasis role="bold">By default, only the source address is checked against the blacklists</emphasis>. Blacklists only stop blacklisted hosts from connecting to you — they do not stop you or your users from connecting to blacklisted hosts .</para> <variablelist> <varlistentry> <term>UPDATE</term> <listitem> <para>Beginning with Shorewall 4.4.12, you can also blacklist by destination address. See <ulink url="manpages/shorewall-blacklist.html">shorewall-blacklist</ulink> (5) and <ulink url="manpages/shorewall.html">shorewall</ulink> (8) for details.</para> </listitem> </varlistentry> </variablelist> </important> <important> <para><emphasis role="bold">Dynamic Shorewall blacklisting is not appropriate for blacklisting 1,000s of different addresses. Static Blacklisting can handle large blacklists but only if you use ipsets</emphasis>. Without ipsets, the blacklists will take forever to load, and will have a very negative effect on firewall performance.</para> </important> <section id="Static"> <title>Static Blacklisting</title> <para>Shorewall static blacklisting support has the following configuration parameters:</para> <itemizedlist> <listitem> <para>You specify whether you want packets from blacklisted hosts dropped or rejected using the BLACKLIST_DISPOSITION setting in <ulink url="manpages/shorewall.conf.html"><filename>shorewall.conf</filename>(5).</ulink></para> </listitem> <listitem> <para>You specify whether you want packets from blacklisted hosts logged and at what syslog level using the BLACKLIST_LOGLEVEL setting in <ulink url="manpages/shorewall.conf.html"><filename>shorewall.conf</filename></ulink>(5).</para> </listitem> <listitem> <para>You list the IP addresses/subnets that you wish to blacklist in <ulink url="manpages/shorewall-blacklist.html"><filename>shorewall-blacklist</filename></ulink> (5). You may also specify PROTOCOL and Port numbers/Service names in the blacklist file.</para> </listitem> <listitem> <para>You specify the interfaces whose incoming packets you want checked against the blacklist using the <quote>blacklist</quote> option in <ulink url="manpages/shorewall-interfaces.html"><filename>shorewall-interfaces</filename></ulink>(5) (<ulink url="manpages/shorewall-zones.html">shorewall-zones</ulink>(5) in Shorewall 4.4.12 and later).</para> </listitem> </itemizedlist> <para>Prior to Shorewall 4.4.20, only source-address static blacklisting was supported.</para> <para>Users with a large static black list may want to set the DELAYBLACKLISTLOAD option in shorewall.conf (added in Shorewall version 2.2.0). When DELAYBLACKLISTLOAD=Yes, Shorewall will enable new connections before loading the blacklist rules. While this may allow connections from blacklisted hosts to slip by during construction of the blacklist, it can substantially reduce the time that all new connections are disabled during "shorewall [re]start".</para> <para>Beginning with Shorewall 2.4.0, you can use <ulink url="ipsets.html">ipsets</ulink> to define your static blacklist. Here's an example:</para> <programlisting>#ADDRESS/SUBNET PROTOCOL PORT +Blacklistports[dst] +Blacklistnets[src,dst] +Blacklist[src,dst] #LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting> <para>In this example, there is a portmap ipset <emphasis>Blacklistports</emphasis> that blacklists all traffic with destination ports included in the ipset. There are also <emphasis>Blacklistnets</emphasis> (type <emphasis>nethash</emphasis>) and <emphasis>Blacklist</emphasis> (type <emphasis>iphash</emphasis>) ipsets that allow blacklisting networks and individual IP addresses. Note that [src,dst] is specified so that individual entries in the sets can be bound to other portmap ipsets to allow blacklisting (<emphasis>source address</emphasis>, <emphasis>destination port</emphasis>) combinations. For example:</para> <programlisting>ipset -N SMTP portmap --from 1 --to 31 ipset -A SMTP 25 ipset -A Blacklist 206.124.146.177 ipset -B Blacklist 206.124.146.177 -b SMTP</programlisting> <para>This will blacklist SMTP traffic from host 206.124.146.177.</para> </section> <section id="whitelisting"> <title>Static Whitelisting</title> <para>Beginning with Shorewall 4.4.20, you can create <firstterm>whitelist</firstterm> entries in the blacklist file. Connections/packets matching a whitelist entry are not matched against the entries in the blacklist file that follow. Whitelist entries are created using the <emphasis role="bold">whitelist</emphasis> option (OPTIONS column). See <ulink url="manpages/shorewall-blacklist.html"><filename>shorewall-blacklist</filename></ulink> (5).</para> </section> <section id="Dynamic"> <title>Dynamic Blacklisting</title> <para>Beginning with Shorewall 4.4.7, dynamic blacklisting is enabled by setting DYNAMIC_BLACKLIST=Yes in <filename>shorewall.conf</filename>. Prior to that release, the feature is always enabled.</para> <para>Once enabled, dynamic blacklisting doesn't use any configuration parameters but is rather controlled using /sbin/shorewall[-lite] commands. <emphasis role="bold">Note</emphasis> that <emphasis role="bold">to</emphasis> and <emphasis role="bold">from</emphasis> may only be specified when running <emphasis role="bold">Shorewall 4.4.12 or later</emphasis>.</para> <itemizedlist> <listitem> <para>drop [to|from] <emphasis><ip address list></emphasis> - causes packets from the listed IP addresses to be silently dropped by the firewall.</para> </listitem> <listitem> <para>reject [to|from]<emphasis><ip address list></emphasis> - causes packets from the listed IP addresses to be rejected by the firewall.</para> </listitem> <listitem> <para>allow [to|from] <emphasis><ip address list></emphasis> - re-enables receipt of packets from hosts previously blacklisted by a <emphasis>drop</emphasis> or <emphasis>reject</emphasis> command.</para> </listitem> <listitem> <para>save - save the dynamic blacklisting configuration so that it will be automatically restored the next time that the firewall is restarted.</para> <para><emphasis role="bold">Update:</emphasis> Beginning with Shorewall 4.4.10, the dynamic blacklist is automatically retained over <command>stop/start</command> sequences and over <command>restart</command>.</para> </listitem> <listitem> <para>show dynamic - displays the dynamic blacklisting configuration.</para> </listitem> <listitem> <para>logdrop [to|from] <emphasis><ip address list></emphasis> - causes packets from the listed IP addresses to be dropped and logged by the firewall. Logging will occur at the level specified by the BLACKLIST_LOGLEVEL setting at the last [re]start (logging will be at the 'info' level if no BLACKLIST_LOGLEVEL was given).</para> </listitem> <listitem> <para>logreject [to|from}<emphasis><ip address list></emphasis> - causes packets from the listed IP addresses to be rejected and logged by the firewall. Logging will occur at the level specified by the BLACKLIST_LOGLEVEL setting at the last [re]start (logging will be at the 'info' level if no BLACKLIST_LOGLEVEL was given).</para> </listitem> </itemizedlist> <para>Dynamic blacklisting is not dependent on the <quote>blacklist</quote> option in <filename>/etc/shorewall/interfaces</filename>.</para> <example id="Ignore"> <title>Ignore packets from a pair of systems</title> <programlisting> <command>shorewall[-lite] drop 192.0.2.124 192.0.2.125</command></programlisting> <para>Drops packets from hosts 192.0.2.124 and 192.0.2.125</para> </example> <example id="Allow"> <title>Re-enable packets from a system</title> <programlisting> <command>shorewall[-lite] allow 192.0.2.125</command></programlisting> <para>Re-enables traffic from 192.0.2.125.</para> </example> <example> <title>Displaying the Dynamic Blacklist</title> <programlisting> <command>shorewall show dynamic</command></programlisting> <para>Displays the 'dynamic' chain which contains rules for the dynamic blacklist. The <firstterm>source</firstterm> column contains the set of blacklisted addresses.</para> </example> </section> </section> </article>