| 1 | <sect3 id="postlfs-security-fw-persFw" xreflabel="Personal Firewall">
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| 2 | <title>Personal Firewall</title>
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| 3 |
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| 4 | <para>A Personal Firewall is supposed to let you access the all services
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| 5 | offered on the internet, but keep your box secure and your data private.</para>
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| 6 |
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| 7 | <para>Below is a slightly modified version of Rusty Russell's
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| 8 | recommendation from the <ulink
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| 9 | url="http://netfilter.samba.org/unreliable-guides/packet-filtering-HOWTO/packet-filtering-HOWTO.linuxdoc-5.html">Linux
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| 10 | 2.4 Packet Filtering HOWTO</ulink>:</para>
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| 11 |
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| 12 | <screen><userinput><command>cat > /etc/rc.d/init.d/firewall << "EOF"</command>
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| 13 | #!/bin/sh
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| 14 |
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| 15 | # Begin $rc_base/init.d/firewall
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| 16 |
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| 17 | # Insert connection-tracking modules (not needed if built into the kernel).
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| 18 | modprobe ip_tables
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| 19 | modprobe iptable_filter
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| 20 | modprobe ip_conntrack
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| 21 | modprobe ip_conntrack_ftp
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| 22 | modprobe ipt_state
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| 23 | modprobe ipt_LOG
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| 24 |
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| 25 | # allow local-only connections
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| 26 | iptables -A INPUT -i lo -j ACCEPT
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| 27 | # free output on any interface to any ip for any service (equal to -P ACCEPT)
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| 28 | iptables -A OUTPUT -j ACCEPT
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| 29 |
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| 30 | # permit answers on already established connections
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| 31 | # and permit new connections related to established ones (eg active-ftp)
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| 32 | iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
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| 33 |
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| 34 | # Log everything else: What's Windows' latest exploitable vulnerability?
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| 35 | iptables -A INPUT -j LOG --log-prefix "FIREWALL:INPUT "
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| 36 |
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| 37 | # set a sane policy: everything not accepted > /dev/null
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| 38 | iptables -P INPUT DROP
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| 39 | iptables -P FORWARD DROP
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| 40 | iptables -P OUTPUT DROP
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| 41 |
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| 42 | # be verbose on dynamic ip-addresses (not needed in case of static IP)
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| 43 | echo 2 > /proc/sys/net/ipv4/ip_dynaddr
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| 44 |
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| 45 | # disable ExplicitCongestionNotification - too many routers are still ignorant
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| 46 | echo 0 > /proc/sys/net/ipv4/tcp_ecn
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| 47 |
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| 48 | # End $rc_base/init.d/firewall
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| 49 | <command>EOF</command></userinput></screen>
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| 50 |
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| 51 | <para>His script is quite simple, it drops all traffic coming in into your
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| 52 | computer that wasn't initiated from your box, but as long as you are simply
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| 53 | surfing the internet you are unlikely to exceed its limits.</para>
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| 54 |
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| 55 | <para>If you frequently encounter certain delays at accessing ftp-servers,
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| 56 | please have a look at <xref linkend="postlfs-security-fw-busybox"/> -
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| 57 | <xref linkend="postlfs-security-fw-BB-4"/>.</para>
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| 58 |
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| 59 | <para>Even if you have daemons / services running on your box, these
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| 60 | should be inaccessible everywhere but from your box itself.
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| 61 | If you want to allow access to services on your machine, such as ssh or pinging,
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| 62 | take a look at <xref linkend="postlfs-security-fw-busybox"/>.</para>
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| 63 |
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| 64 | </sect3>
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