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Document hack to work around L2TP vulnerability
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@8408 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
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@ -786,20 +786,26 @@ all all REJECT info
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#LAST LINE -- ADD YOUR ENTRIES ABOVE THIS LINE -- DO NOT REMOVE</programlisting>
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</blockquote>
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<para>The final step is to modify your rules file. There are two important
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components. First, you must allow the l2tp traffic to reach the xl2tpd
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process running on the firewall machine. Second, you must add rules to
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open up ports on the firewall to the road warrior for services which are
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running on the firewall. For example, if you are running a webserver on
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the firewall that must be accessible to road warriors. The reason for the
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second step is that the policy does not by default allow unrestricted
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access to the firewall itself.</para>
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<para>The final step is to modify your rules file. There are three
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important components. First, you must allow the l2tp traffic to reach the
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xl2tpd process running on the firewall machine. Second, you must add rules
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to open up ports on the firewall to the road warrior for services which
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are running on the firewall. For example, if you are running a webserver
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on the firewall that must be accessible to road warriors. The reason for
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the second step is that the policy does not by default allow unrestricted
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access to the firewall itself. Finally, you should protect an exploit
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where an attacker can exploit your LT2P server do to a hole in the way
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that L2TP interacts with UDP connection tracking.</para>
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<blockquote>
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<para><filename>/etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE
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# PORT(S) PORT(S)
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SECTION ESTABLISHED
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# Prevent IPSEC bypass by hosts behind a NAT gateway
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L2TP/REJECT net $FW
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REJECT $FW net udp - 1701
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# l2tp over the IPsec VPN
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ACCEPT vpn $FW udp 1701
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# webserver that can only be accessed internally
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