[v2,2/3] proxy.cgi: Implement proactive Fast Flux detection and detection for selectively announced destinations

  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.

The second version of this patch consumes the user-defined whitelist for
the URL filter (if present and populated) for the ASNBL helper as well,
to make exceptions for funny destinations such as fedoraproject.org
possible. In addition, the ASNBL helper's sanity tests no longer include
publicly routable IP addresses, so failures on location01 cannot brick
IPFire installations in the field.

Thanks to Michael Tremer and Adolf Belka for these suggestions.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
---
 html/cgi-bin/proxy.cgi | 98 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
  

Looks okay to me now. Thank you for working on this.

Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>

> On 10 Oct 2021, at 18:43, Peter Müller <peter.mueller@ipfire.org> wrote:
> 
> 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.
> 
> The second version of this patch consumes the user-defined whitelist for
> the URL filter (if present and populated) for the ASNBL helper as well,
> to make exceptions for funny destinations such as fedoraproject.org
> possible. In addition, the ASNBL helper's sanity tests no longer include
> publicly routable IP addresses, so failures on location01 cannot brick
> IPFire installations in the field.
> 
> Thanks to Michael Tremer and Adolf Belka for these suggestions.
> 
> Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
> ---
> html/cgi-bin/proxy.cgi | 98 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 98 insertions(+)
> 
> diff --git a/html/cgi-bin/proxy.cgi b/html/cgi-bin/proxy.cgi
> index 966593e4d..202a8f3bc 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;
> @@ -229,6 +230,9 @@ $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';
> $proxysettings{'AUTH_REALM'} = '';
> @@ -418,6 +422,21 @@ if (($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') &&
> @@ -801,6 +820,14 @@ $selected{'THROTTLING_GREEN_HOST'}{$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'";
> @@ -1633,6 +1660,24 @@ 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' $checked{'ASNBL_SELECANN_DETECTION'}{'on'} /></td>
> +</tr>
> +</table>
> +
> <hr size='1'>
> END
> ;
> @@ -3525,6 +3570,59 @@ if (@ssl_ports) {
> 	print FILE "http_access deny  CONNECT !SSL_ports\n";
> }
> 
> +	if ((($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 ${General::swroot}/proxy/asnbl-helper.conf\n";
> +		print FILE "acl asnbl external asnblhelper\n";
> +
> +		# Use the user-defined URL filter whitelist (if present and populated) for the ASNBL helper as well
> +		# Necessary for destinations such as fedoraproject.org, but we do not want to maintain a dedicated
> +		# or hardcoded list for such FQDNs.
> +		if ((-e "${General::swroot}/urlfilter/blacklists/custom/allowed/domains") && (!-z "${General::swroot}/urlfilter/blacklists/custom/allowed/domains")) {
> +			print FILE "acl asnbl_whitelisted_destinations dstdomain \"${General::swroot}/urlfilter/blacklists/custom/allowed/domains\"\n";
> +			print FILE "http_access deny asnbl !asnbl_whitelisted_destinations\n\n";
> +		} else {
> +			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 ($proxysettings{'ASNBL_FASTFLUX_DETECTION'} eq 'on') {
> +			print ASNBLFILE "BLOCK_DIVERSITY_EXCEEDING_DESTINATIONS = yes\n";
> +		} else {
> +			print ASNBLFILE "BLOCK_DIVERSITY_EXCEEDING_DESTINATIONS = no\n";
> +		}
> +
> +		print ASNBLFILE<<END
> +TESTDATA = (10.0.0.1, 0) (127.0.0.1, 0) (fe80::1, 0)
> +ACTIVE_ASNBLS = 
> +END
> +;
> +
> +		close ASNBLFILE;
> +    }
> +
> if ($proxysettings{'AUTH_METHOD'} eq 'ident')
> {
> print FILE "#Set ident ACLs\n";
> -- 
> 2.26.2