[PATCH 2/3] proxy.cgi: Implement proactive Fast Flux detection and detection for selectively announced destinations

["Peter Müller" <peter.mueller@ipfire.org>]

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This patch adds two new features to IPFire's web proxy:

(a) Proactive Fast Flux detection
    FQDNs are resolved to their IP addresses, which are then resolved to
    corresponding Autonomous System Numbers using IPFire's location
    database. Most destinations will scatter across a very low number of
    ASNs (not to be confused with IP addresses!). FQDNs hosted on Fast
    Flux setups have a significantly higher ASN diversity (5 is usually
    a good threshold), so they can be proactively detected.

(b) Detection for selectively announced destinations
    Especially in targeted operations, miscreants host FQDNs for
    exfiltrating data or malware distributions on ASNs not announced
    globally, but only to the intended victim or it's upstream ISPs.

    That way, security researchers located in other parts of the
    internet have no insights into these attacks, hence not being able
    to publish listings or send take down notices for the domains used.

    While RPKI made this attack harder, it can still be observed every
    now and then.

    This feature also protects against accessing FQDNs resolving to IP
    addresses not being globally routeable, hence providing a trivial
    mitigation for so-called "rebound attacks" - which we cannot filter
    at DNS level currently.

Signed-off-by: Peter Müller <peter.mueller(a)ipfire.org>
---
 html/cgi-bin/proxy.cgi | 89 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/html/cgi-bin/proxy.cgi b/html/cgi-bin/proxy.cgi
index 78ad33ad2..b7227deaf 100644
--- a/html/cgi-bin/proxy.cgi
+++ b/html/cgi-bin/proxy.cgi
@@ -21,6 +21,7 @@
 
 use strict;
 use Apache::Htpasswd;
+use Scalar::Util qw(looks_like_number);
 
 # enable only the following on debugging purpose
 #use warnings;
@@ -225,6 +226,9 @@ $proxysettings{'THROTTLING_GREEN_TOTAL'} = 'unlimited';
 $proxysettings{'THROTTLING_GREEN_HOST'} = 'unlimited';
 $proxysettings{'THROTTLING_BLUE_TOTAL'} = 'unlimited';
 $proxysettings{'THROTTLING_BLUE_HOST'} = 'unlimited';
+$proxysettings{'ASNBL_FASTFLUX_DETECTION'} = 'off';
+$proxysettings{'ASNBL_FASTFLUX_THRESHOLD'} = '5';
+$proxysettings{'ASNBL_SELECANN_DETECTION'} = 'off';
 $proxysettings{'ENABLE_MIME_FILTER'} = 'off';
 $proxysettings{'AUTH_METHOD'} = 'none';
 $proxysettings{'AUTH_REALM'} = '';
@@ -414,6 +418,21 @@ if (($proxysettings{'ACTION'} eq $Lang::tr{'save'}) || ($proxysettings{'ACTION'}
 		$errormessage = $Lang::tr{'invalid maximum incoming size'};
 		goto ERROR;
 	}
+	if (($proxysettings{'ASNBL_FASTFLUX_DETECTION'} eq 'on') || ($proxysettings{'ASNBL_SELECANN_DETECTION'} eq 'on'))
+	{
+		if (-z $proxysettings{'ASNBL_FASTFLUX_THRESHOLD'}) {
+			$errormessage = $Lang::tr{'advproxy fastflux no threshold given'};
+			goto ERROR;
+		}
+		if (! looks_like_number($proxysettings{'ASNBL_FASTFLUX_THRESHOLD'})) {
+			$errormessage = $Lang::tr{'advproxy fastflux threshold invalid'};
+			goto ERROR;
+		}
+		if (($proxysettings{'ASNBL_FASTFLUX_THRESHOLD'} < 2) || ($proxysettings{'ASNBL_FASTFLUX_THRESHOLD'} > 10)) {
+			$errormessage = $Lang::tr{'advproxy fastflux threshold out of bounds'};
+			goto ERROR;
+		}
+	}
 	if (!($proxysettings{'AUTH_METHOD'} eq 'none'))
 	{
 		unless (($proxysettings{'AUTH_METHOD'} eq 'ident') &&
@@ -797,6 +816,14 @@ $selected{'THROTTLING_GREEN_HOST'}{$proxysettings{'THROTTLING_GREEN_HOST'}} = "s
 $selected{'THROTTLING_BLUE_TOTAL'}{$proxysettings{'THROTTLING_BLUE_TOTAL'}} = "selected='selected'";
 $selected{'THROTTLING_BLUE_HOST'}{$proxysettings{'THROTTLING_BLUE_HOST'}} = "selected='selected'";
 
+$checked{'ASNBL_FASTFLUX_DETECTION'}{'off'} = '';
+$checked{'ASNBL_FASTFLUX_DETECTION'}{'on'} = '';
+$checked{'ASNBL_FASTFLUX_DETECTION'}{$proxysettings{'ASNBL_FASTFLUX_DETECTION'}} = "checked='checked'";
+
+$checked{'ASNBL_SELECANN_DETECTION'}{'off'} = '';
+$checked{'ASNBL_SELECANN_DETECTION'}{'on'} = '';
+$checked{'ASNBL_SELECANN_DETECTION'}{$proxysettings{'ASNBL_SELECANN_DETECTION'}} = "checked='checked'";
+
 $checked{'ENABLE_MIME_FILTER'}{'off'} = '';
 $checked{'ENABLE_MIME_FILTER'}{'on'} = '';
 $checked{'ENABLE_MIME_FILTER'}{$proxysettings{'ENABLE_MIME_FILTER'}} = "checked='checked'";
@@ -1627,6 +1654,24 @@ END
 print <<END
 </table>
 
+<hr size='1'>
+
+<table width='100%'>
+<tr>
+       <td><b>$Lang::tr{'advproxy asbased anomaly detection'}</b></td>
+</tr>
+<tr>
+       <td class='base'>$Lang::tr{'advproxy fastflux detection'}:</td>
+       <td><input type='checkbox' name='ASNBL_FASTFLUX_DETECTION' $checked{'ASNBL_FASTFLUX_DETECTION'}{'on'} /></td>
+       <td class='base'>$Lang::tr{'advproxy fastflux detection threshold'}:</td>
+       <td><input type='text' name='ASNBL_FASTFLUX_THRESHOLD' value='$proxysettings{'ASNBL_FASTFLUX_THRESHOLD'}' size=2 /></td>
+</tr>
+<tr>
+       <td class='base'>$Lang::tr{'advproxy selectively announcements detection'}:</td>
+       <td colspan='3'><input type='checkbox' name='ASNBL_SELECANN_DETECTION' $checked{'ASNBL_SELECANN_DETECTION'}{'on'} /></td>
+</tr>
+</table>
+
 <hr size='1'>
 END
 ;
@@ -3507,6 +3552,50 @@ if (@ssl_ports) {
 	print FILE "http_access deny  CONNECT !SSL_ports\n";
 }
 
+	if ((($proxysettings{'ASNBL_FASTFLUX_DETECTION'} eq 'on') && (!-z $proxysettings{'ASNBL_FASTFLUX_THRESHOLD'})) || ($proxysettings{'ASNBL_SELECANN_DETECTION'} eq 'on')) {
+		print FILE "external_acl_type asnblhelper children-max=10 children-startup=2 ttl=86400 %DST /usr/bin/asnbl-helper.py /var/ipfire/proxy/asnbl-helper.conf\n";
+		print FILE "acl asnbl external asnblhelper\n";
+		print FILE "http_access deny asnbl\n\n";
+
+		# Write ASNBL helper configuration file...
+		open(ASNBLFILE, ">${General::swroot}/proxy/asnbl-helper.conf");
+		flock(ASNBLFILE, 2);
+
+		print ASNBLFILE<<END
+#
+# This file has been automatically generated. Manual changes will be overwritten.
+#
+
+[GENERAL]
+LOGLEVEL = INFO
+ASNDB_PATH = /var/lib/location/database.db
+USE_REPLYMAP = no
+END
+;
+
+		print ASNBLFILE "AS_DIVERSITY_THRESHOLD = $proxysettings{'ASNBL_FASTFLUX_THRESHOLD'}\n";
+
+		if ($proxysettings{'ASNBL_SELECANN_DETECTION'} eq 'on') {
+			print ASNBLFILE "BLOCK_SUSPECTED_SELECTIVE_ANNOUNCEMENTS = yes\n";
+		} else {
+			print ASNBLFILE "BLOCK_SUSPECTED_SELECTIVE_ANNOUNCEMENTS = no\n";
+		}
+
+		if ($proxysettings{'ASNBL_FASTFLUX_DETECTION'} eq 'on') {
+			print ASNBLFILE "BLOCK_DIVERSITY_EXCEEDING_DESTINATIONS = yes\n";
+		} else {
+			print ASNBLFILE "BLOCK_DIVERSITY_EXCEEDING_DESTINATIONS = no\n";
+		}
+
+		print ASNBLFILE<<END
+TESTDATA = (1.1.1.1, 13335) (8.8.8.8, 15169) (194.95.245.140, 680) (10.0.0.1, 0) (127.0.0.1, 0) (2001:638:d:c102::140, 680) (2606:4700:10::6814:d673, 13335) (fe80::1, 0)
+ACTIVE_ASNBLS = 
+END
+;
+
+		close ASNBLFILE;
+    }
+
 if ($proxysettings{'AUTH_METHOD'} eq 'ident')
 {
 print FILE "#Set ident ACLs\n";
-- 
2.26.2