<?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 Events</title> <authorgroup> <author> <firstname>Tom</firstname> <surname>Eastep</surname> </author> </authorgroup> <pubdate><?dbtimestamp format="Y/m/d"?></pubdate> <copyright> <year>2013</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>This article applies to Shorewall 4.5.19 and later and supercedes <ulink url="PortKnocking.html">this article.</ulink></para> </caution> <section> <title>Overview</title> <para>Shorewall events were introduced in Shorewall 4.5.19 and provide a high-level interface to the Netfilter<firstterm> recent match</firstterm> capability. An event is actually a list of (IP address, timestamp) pairs, and can be tested in a number of different ways:</para> <itemizedlist> <listitem> <para>Has event E ever occurred for IP address A (is the IP address in the list)?</para> </listitem> <listitem> <para>Has event E occurred M or more times for IP address A?</para> </listitem> <listitem> <para>Has Event E occurred in the last N seconds for IP Address A (is there an entry for the address with a timestamp falling within the last N seconds)?</para> </listitem> <listitem> <para>Has Event E occurred M or more times in the last N seconds for IP address A (are there M or more entries for the address with timestamps falling within the last N seconds)?</para> </listitem> </itemizedlist> <para>The event interface is implemented as three parameterized Shorewall <ulink url="Actions.html">Actions</ulink>:</para> <variablelist> <varlistentry> <term>SetEvent</term> <listitem> <para>This action initializes an event list for either the source or destination IP address in the current packets. The list will contain a single entry for the address that will have the current timestamp.</para> </listitem> </varlistentry> <varlistentry> <term>ResetEvent</term> <listitem> <para>This action removes all entries for either the source or destination IP address from an event list.</para> </listitem> </varlistentry> <varlistentry> <term>IfEvent</term> <listitem> <para>This action tests an event in one of the ways listed above, and performs an action based on the result.</para> </listitem> </varlistentry> </variablelist> <para>Events are based on the Netfilter 'recent match' capability which is required for their use.</para> <para>The recent-match kernel component is xt_recent which has two options that are of interest to Shorewall users:</para> <variablelist> <varlistentry> <term>ip_list_tot</term> <listitem> <para>The number of addresses remembered per event. Default is 100.</para> </listitem> </varlistentry> <varlistentry> <term>ip_pkt_list_tot</term> <listitem> <para>The number of packets (event occurrences) remembered per address. Default is 20.</para> </listitem> </varlistentry> </variablelist> <para>These may be changed with the xt_recent module is loaded or on the kernel bootloader runline.</para> </section> <section> <title>Details</title> <para>Because these are parameterized actions, optional parameters may be omitted. Trailing omitted parameters may be omitted entirely while embedded omitted parameters are represented by a hyphen ("-").</para> <para>Each event is given a name. Event names:</para> <itemizedlist> <listitem> <para>Must begin with a letter.</para> </listitem> <listitem> <para>May be composed of letters, digits, hyphens ('-') or underscores ('_').</para> </listitem> <listitem> <para>May be at most 29 characters in length.</para> </listitem> </itemizedlist> <section id="SetEvent"> <title>SetEvent</title> <para><emphasis role="bold">SetEvent</emphasis>( <replaceable>event</replaceable>, [ <replaceable>action</replaceable> ], [ <replaceable>src-dst</replaceable> ], [ <replaceable>disposition</replaceable> ] )</para> <variablelist> <varlistentry> <term>event</term> <listitem> <para>Name of the event.</para> </listitem> </varlistentry> <varlistentry> <term>action</term> <listitem> <para>An action to perform after the event is initialized. May be any action that may appear in the ACTION column of <ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5). If no action is to be performed, use COUNT.</para> </listitem> </varlistentry> <varlistentry> <term>src-dst</term> <listitem> <para>Specifies whether the source IP address (<emphasis role="bold">src</emphasis>) or destination IP address (<emphasis role="bold">dst</emphasis>) is to be added to the event. The default is <emphasis role="bold">src</emphasis>.</para> </listitem> </varlistentry> <varlistentry> <term>disposition</term> <listitem> <para>If the <replaceable>action</replaceable> involves logging, then this parameter specifies the disposition that will appear in the log entry prefix. If no <replaceable>disposition</replaceable> is given, the log prefix is determines normally. The default is ACCEPT.</para> </listitem> </varlistentry> </variablelist> </section> <section id="ResetEvent"> <title>ResetEvent</title> <para><emphasis role="bold">ResetEvent</emphasis>( <replaceable>event</replaceable>, [ <replaceable>action</replaceable> ], [ <replaceable>src-dst</replaceable> ], [ <replaceable>disposition</replaceable> ] )</para> <variablelist> <varlistentry> <term>event</term> <listitem> <para>Name of the event.</para> </listitem> </varlistentry> <varlistentry> <term>action</term> <listitem> <para>An action to perform after the event is reset. May be any action that may appear in the ACTION column of <ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5). If no action is to be performed, use COUNT. The default is ACCEPT.</para> </listitem> </varlistentry> <varlistentry> <term>src-dst</term> <listitem> <para>Specifies whether the source IP address (<emphasis role="bold">src</emphasis>) or destination IP address (<emphasis role="bold">dst</emphasis>) is to be removed from the event. The default is <emphasis role="bold">src</emphasis>.</para> </listitem> </varlistentry> <varlistentry> <term>disposition</term> <listitem> <para>If the <replaceable>action</replaceable> involves logging, then this parameter specifies the disposition that will appear in the log entry prefix. If no <replaceable>disposition</replaceable> is given, the log prefix is determines normally.</para> </listitem> </varlistentry> </variablelist> </section> <section id="IfEvent"> <title>IfEvent</title> <para><emphasis role="bold">IfEvent</emphasis>( <replaceable>event</replaceable>, [ <replaceable>action</replaceable> ], [ <replaceable>duration</replaceable> ], [ <replaceable>hitcount</replaceable> ], [ <replaceable>src-dst</replaceable>], [ <replaceable>command</replaceable>[:<replaceable>option</replaceable>]..., [ <replaceable>disposition</replaceable> ] )</para> <variablelist> <varlistentry> <term>event</term> <listitem> <para>Name of the event.</para> </listitem> </varlistentry> <varlistentry> <term>action</term> <listitem> <para>An action to perform if the test succeeds. May be any action that may appear in the ACTION column of <ulink url="manpages/shorewall-rules.html">shorewall-rules</ulink> (5). The default is ACCEPT.</para> </listitem> </varlistentry> <varlistentry> <term>duration</term> <listitem> <para>Number of seconds over which the event is to be tested. If not specified, the test is not constrained by time.</para> </listitem> </varlistentry> <varlistentry> <term>hitcount</term> <listitem> <para>Specifies the minimum number of packets required for the test to succeed. If not specified, 1 packet is assumed.</para> </listitem> </varlistentry> <varlistentry> <term>src-dst</term> <listitem> <para>Specifies whether the source IP address (<emphasis role="bold">src</emphasis>) or destination IP address (<emphasis role="bold">dst</emphasis>) is to be tested. The default is <emphasis role="bold">src</emphasis>.</para> </listitem> </varlistentry> <varlistentry> <term>command</term> <listitem> <para>May be one of the following:</para> <variablelist> <varlistentry> <term>check</term> <listitem> <para>Simply test if the <replaceable>duration</replaceable>/<replaceable>hitcount</replaceable> test is satisfied. If so, the <replaceable>action</replaceable> is performed.</para> </listitem> </varlistentry> <varlistentry> <term>reset</term> <listitem> <para>Like <emphasis role="bold">check</emphasis>. If the test succeeds, the <replaceable>event</replaceable> will be reset before the <replaceable>action</replaceable> is taken. Requires the <firstterm>Mark in filter table</firstterm> capability in your kernel and iptables.</para> </listitem> </varlistentry> <varlistentry> <term>update</term> <listitem> <para>Like <emphasis role="bold">check</emphasis>. Regardless of whether the test succeeds, an entry with the current time and for the <replaceable>src-dst</replaceable> iP address will be added to the <replaceable>event</replaceable>.</para> </listitem> </varlistentry> </variablelist> <para>The default is <emphasis role="bold">check</emphasis>.</para> <para><replaceable>option</replaceable> may be one of:</para> <variablelist> <varlistentry> <term>reap</term> <listitem> <para>Regardless of whether the test succeeds, entries for the <replaceable>src-dst</replaceable> IP address that are older than <replaceable>duration</replaceable> seconds will be deleted from the <replaceable>event</replaceable>.</para> </listitem> </varlistentry> <varlistentry> <term>ttl</term> <listitem> <para>Constrains the test to require that the packet TTL match the ttl in the original packet that created the entry.</para> </listitem> </varlistentry> </variablelist> </listitem> </varlistentry> <varlistentry> <term>disposition</term> <listitem> <para>If the <replaceable>action</replaceable> involves logging, then this parameter specifies the disposition that will appear in the log entry prefix. If no <replaceable>disposition</replaceable> is given, the log prefix is determines normally.</para> </listitem> </varlistentry> </variablelist> </section> <section id="ShowEvents"> <title>'show event' and 'show events' Commands</title> <para>The CLI programs (<filename>/sbin/shorewall</filename>, <filename>/sbin/shorewall-lite</filename>, etc.) support <command>show event</command> and <command>show events</command> commands.</para> <para>The <command>show event</command> command shows the contents of the events listed in the command while <emphasis role="bold">show events</emphasis> lists the contents of all events.</para> <programlisting>root@gateway:~# shorewall show events Shorewall 4.5.19-Beta2 events at gateway - Sat Jul 13 07:17:59 PDT 2013 SSH src=75.101.251.91 : 2225.808, 2225.592 src=218.87.16.135 : 2078.490 SSH_COUNTER src=65.182.111.112 : 5755.790 src=113.162.155.243 : 4678.249 sticky001 src=172.20.1.146 : 5.733, 5.728, 5.623, 5.611, 5.606, 5.606, 5.589, 5.588, 5.565, 5.551, 5.543, 5.521, 5.377, 5.347, 5.347, 5.345, 5.258, 5.148, 5.048, 4.949 src=172.20.1.151 : 41.805, 41.800 sticky002 src=172.20.1.213 : 98.122, 98.105, 98.105, 98.105, 98.088, 98.088, 98.088, 98.088, 98.058, 98.058, 80.885, 53.528, 53.526, 53.526, 53.510, 53.383, 53.194, 53.138, 53.072, 3.119 src=172.20.1.146 : 4.914, 4.914, 4.898, 4.897, 4.897, 4.896, 4.896, 4.896, 4.882, 4.881, 4.875, 4.875, 4.875, 4.875, 4.875, 4.875, 4.875, 4.874, 4.874, 4.874 root@gateway:~# </programlisting> <para>The SSH and SSH_COUNTER events are created using the following Automatic Blacklisting example. The sticky001 and sticky002 events are created by the SAME rule action.</para> <para>Each line represents one event. The list of numbers following the ':' represent the number of seconds ago that a matching packet triggered the event. The numbers are in chronological sequence, so In this event, there were 20 packets from 172.20.1.146 that arrived between 5.733 and 4.949 seconds ago:</para> <programlisting>sticky001 src=172.20.1.146 : <emphasis role="bold">5.733</emphasis>, 5.728, 5.623, 5.611, 5.606, 5.606, 5.589, 5.588, 5.565, 5.551, 5.543, 5.521, 5.377, 5.347, 5.347, 5.345, 5.258, 5.148, 5.048, <emphasis role="bold">4.949</emphasis> </programlisting> <para>Note that there may have been earlier packets that also matched, but the system where this example was captured used the default value of the <emphasis role="bold">ip_pkt_list_tot</emphasis> xt_recent option (20).</para> <para>The output of these commands is produced by processing the contents of <filename>/proc/net/xt_recent/*</filename>. You can access those files directly to see the raw data. The raw times are the uptime in milliseconds. The %CURRENTTIME entry is created by the <command>show event[s]</command> commands to obtain the current uptime.</para> </section> </section> <section> <title>Examples</title> <section> <title>Automatic Blacklisting</title> <para>This example is taken from <ulink url="http://www.briandowney.net/blog/2009/08/20/firewalling-brute-force-attempts-with-iptables/">this article</ulink> which explains the nice benifits of this approach. This example is for ssh, but it can be adapted for any application.</para> <para>The name SSH has been changed to SSHLIMIT so as not to override the Shorewall macro of the same name.</para> <para><filename>/etc/shorewall/actions</filename>:</para> <programlisting>#ACTION OPTION DESCRIPTION SSHLIMIT #Automatically blacklist hosts who exceed SSH connection limits SSH_BLACKLIST #Helper for SSHLIMIT</programlisting> <para><filename>/etc/shorewall/action.SSH_BLACKLIST</filename>:</para> <programlisting># # Shorewall version 4 - SSH_BLACKLIST Action # ?format 2 ############################################################################### #TARGET SOURCE DEST PROTO DPORT SPORT # # Log the Reject # LOG:warn:REJECT # # And set the SSH_COUNTER event for the SOURCE IP address # SetEvent(SSH_COUNTER,REJECT,src)</programlisting> <para><filename>/etc/shorewall/action.SSH</filename>LIMIT:</para> <programlisting># # Shorewall version 4 - SSHLIMIT Action # ?format 2 ############################################################################### #TARGET SOURCE DEST PROTO DPORT SPORT # # Silently reject the client if blacklisted # IfEvent(SSH_COUNTER,REJECT,300,1) # # Blacklist if 5 attempts in the last minute # IfEvent(SSH,SSH_BLACKLIST,60,5,src,check:reap) # # Log and reject if the client has tried to connect # in the last two seconds # IfEvent(SSH,REJECT:warn:,2,1,-,update,Added) # # Un-blacklist the client # ResetEvent(SSH_COUNTER,LOG:warn,-,Removed) # # Set the 'SSH' EVENT and accept the connection # SetEvent(SSH,ACCEPT,src)</programlisting> <para><filename>etc/shorewall/rules</filename>:</para> <programlisting>#ACTION SOURCE DEST PROTO DEST # PORT(S) SSHLIMIT net $FW tcp 22 </programlisting> <caution> <para>The technique demonstrated in this example is not self-cleaning. The SSH_COUNTER event can become full with blackisted addresses that never attempt to connect again. When that happens and a new entry is added via SetEvent, the least recently seen address in the table is deleted.</para> </caution> </section> <section id="AutoBL"> <title>Generalized Automatic Blacklisting</title> <para>The above two actions are generalized in the AutoBL and AutoBLL actions released in Shorewall 4.5.19. Only AutoBL is invoked directly from your rules file; AutoBL invoked AutoBLL internally.</para> <section> <title>AutoBL</title> <para><emphasis role="bold">AutoBL</emphasis>( <replaceable>event</replaceable>, [ <replaceable>Interval</replaceable> ], [ <replaceable>hitcount</replaceable> ], [ <replaceable>successive</replaceable> ], [ <replaceable>blacklist-time</replaceable> ], [ <replaceable>disposition </replaceable>], [ <replaceable>log_level</replaceable> ] )</para> <variablelist> <varlistentry> <term>event</term> <listitem> <para>Name of the event. The blacklisting event itself will be <replaceable>event</replaceable>_BL (analogous to SSH_COUNTER above).</para> </listitem> </varlistentry> <varlistentry> <term>interval</term> <listitem> <para>Interval, in seconds, over which hits are to be counted. Default is 60 seconds.</para> </listitem> </varlistentry> <varlistentry> <term>hitcount</term> <listitem> <para>Number of matching packets that will trigger automatic blacklisting when they arrive in <replaceable>interval</replaceable> seconds. Default is 5.</para> </listitem> </varlistentry> <varlistentry> <term>successive</term> <listitem> <para>If a matching packet arrives within this many seconds of the preceding one, it should be logged according to <replaceable>log_level</replaceable> and handled according to the <replaceable>disposition</replaceable>. If successive packets are not to be considered, enter 0. Default is 2 seconds.</para> </listitem> </varlistentry> <varlistentry> <term>blacklist-time</term> <listitem> <para>Time, in seconds, that the source IP address is to be blacklisted. Default is 300 (5 minutes).</para> </listitem> </varlistentry> <varlistentry> <term>disposition</term> <listitem> <para>The disposition of blacklisted packets. Default is DROP.</para> </listitem> </varlistentry> <varlistentry> <term>log_level</term> <listitem> <para>Log level at which packets are to be logged. Default is info.</para> </listitem> </varlistentry> </variablelist> <para>To duplicate the SSHLIMIT entry in <filename>/etc/shorewall/rules</filename> shown above:</para> <programlisting>#ACTION SOURCE DEST PROTO DEST # PORT(S) AutoBL(SSH,-,-,-,REJECT,warn)\ net $FW tcp 22 </programlisting> </section> </section> <section> <title>Port Knocking</title> <para>This example shows a different implementation of the one shown in the <ulink url="PortKnocking.html">Port Knocking</ulink> article.</para> <para>In this example:</para> <orderedlist> <listitem> <para>Attempting to connect to port 1600 enables SSH access. Access is enabled for 60 seconds.</para> </listitem> <listitem> <para>Attempting to connect to port 1601 disables SSH access (note that in the article linked above, attempting to connect to port 1599 also disables access. This is an port scan defence as explained in the article).</para> </listitem> </orderedlist> <para>To implement that approach:</para> <para><filename>/etc/shorewall/actions</filename>:</para> <programlisting>#ACTION OPTION DESCRIPTION Knock #Port Knocking</programlisting> <para><filename>/etc/shorewall/action.Knock</filename>:</para> <programlisting># # Shorewall version 4 - SSH_BLACKLIST Action # ?format 2 ############################################################################### #ACTION SOURCE DEST PROTO DEST # PORT(S) IfEvent(SSH,ACCEPT:info,60,1,src,reset)\ - - tcp 22 SetEvent(SSH,ACCEPT) - - tcp 1600 ResetEvent(SSH,DROP:info) </programlisting> <para><filename>etc/shorewall/rules</filename>:</para> <programlisting>#ACTION SOURCE DEST PROTO DEST # PORT(S) Knock net $FW tcp 22,1599-1601 </programlisting> </section> </section> </article>