Hello *,
by accident, I just stumbled across a false positive related to the Fast Flux detection:
[root@maverick ~]# su squid -s /bin/bash bash-5.1$ /usr/bin/asnbl-helper.py /var/ipfire/proxy/asnbl-helper.conf Sep 06 18:28:21 squid-asnbl-helper[9945] WARN: No ASNBL configured. This is acceptable as long as this script is configured to do anything, you just have been warned... Sep 06 18:28:21 squid-asnbl-helper[9945] INFO: Configuation sanity tests passed, good, processing... Sep 06 18:28:21 squid-asnbl-helper[9945] INFO: Successfully loaded location database from /var/lib/location/database.db generated 'Mon Sep 6 05:52:56 2021' (UTC/GMT) by 'IPFire Project' - good Sep 06 18:28:21 squid-asnbl-helper[9945] INFO: Running ASN database response tests... Sep 06 18:28:21 squid-asnbl-helper[9945] INFO: ASN database operational - excellent. Waiting for input... fedoraproject.org Sep 06 18:28:26 squid-asnbl-helper[9945] WARN: Destination 'fedoraproject.org' exceeds ASN diversity threshold (9 > 5), possibly Fast Flux: [81, 3701, 15456, 16509, 21785, 22753, 36850, 54455, 61317] Sep 06 18:28:26 squid-asnbl-helper[9945] INFO: Denying access to possible Fast Flux destination 'fedoraproject.org' OK
Apparently, the Fedora folks think it is a good idea to use round-robin for load balancing:
$ dig +short a fedoraproject.org 140.211.169.206 67.219.144.68 85.236.55.6 38.145.60.20 152.19.134.198 209.132.190.2 18.133.140.134 18.185.136.17 185.141.165.254 152.19.134.142 38.145.60.21 18.159.254.57
At the first glance, using the URL filter (by adding fedoraproject.org to the list of always allowed domains) seems to be a straight-forward solution to this problem. However, it does not work, as the ASNBL script is executed in the context of an ACL, while the URL filter comes as a redirect/wrapper. Therefore, it is never reached if a "deny" ACL matches in the first place.
This is the only false positive I observed so far. Unfortunately, it is a rather bad one. :-/
Any thoughts on what to do now?
Thanks, and best regards, Peter Müller
Hello Michael,
thank you for your reply.
Hello Peter,
I love this feature. I think it is a one-of-a-kind thing and hopefully many more people will think the same.
Yes, I like the idea, too. Sometimes, security can be simple _and_ effective... :-)
However, it will need a lot of documentation and explaining.
Indeed. I was thinking about a blog post for it; we probably need to explain Fast Flux in the first place, and I am not sure if all of our users are aware of the existence of autonomous systems.
I have a couple of high-level questions:
- Does it make sense to give the user the choice for the threshold?
It seems to be a difficult question because it requires exact knowledge what this feature actually does. My fears are that people just set this to something like “9” and the feature would become ineffective. What use-case is there to change this?
One size never fits all, I guess.
Indeed, the range of useful threshold values is pretty small: Anything below 4 causes _way_ too much false positives in productive environment, whereas even 7 appears to be too ineffective.
At the moment, the CGI catches values the ASNBL helper would treat itself as being invalid. Do you think narrowing down this range to 4 to 7 makes sense? Or should we replace it by a dropdown for adjusting sensitivity?
Either way, it is a good idea to tell users to leave the default where it is unless they truly understand what they are doing.
- Selective announcements: Should this necessarily live in the proxy? Why do we not generate a filter for the firewall?
We can do so as well, and I would love to see such a feature landing in IPFire.
Given our current state of libloc, I doubt this is possible: We would need a function that returns all networks we do not have an AS for - to my knowledge, the libloc (bindings) do not support this at the moment.
Apart from that: On a packet filter level, we lack the FQDN of a destination, which might be useful to have for debugging or forensic reasons.
Also, the users will experience a timeout after n seconds. Having selective announcement detection turned on, they'll get their error message straight away. I was told this improves UX... :-)
Thanks, and best regards, Peter Müller
-Michael
On 18 Jun 2021, at 18:24, Peter Müller peter.mueller@ipfire.org wrote:
This patchset adds two new features to IPFire's web proxy, taking advantage of the Autonomous System information we have at hand by using libloc.
The proactive Fast Flux detection is especially worth noticing, as even most expensive (= advanced?) security suites do not provide similar protection, especially not in a proactive manner.
By simply enumerating the distinct amount of Autonomous System Numbers a FQDN ultimately resolves to, we are able to deny access to malware distribution sites, phishing sites, C&C servers, and other cybercrime stuff hosted on Fast Flux setups abusing cracked machines around the world - even before the FQDN or any IP address involved is flagged as malicious by any security vendor.
Peter Müller (3): squid-asnbl: New package proxy.cgi: Implement proactive Fast Flux detection and detection for selectively announced destinations langs: Add English and German translations for newly added web proxy features
config/rootfiles/common/squid-asnbl | 1 + html/cgi-bin/proxy.cgi | 89 +++++++++++++++++++++++++++++ langs/de/cgi-bin/de.pl | 7 +++ langs/en/cgi-bin/en.pl | 7 +++ lfs/squid-asnbl | 83 +++++++++++++++++++++++++++ make.sh | 1 + 6 files changed, 188 insertions(+) create mode 100644 config/rootfiles/common/squid-asnbl create mode 100644 lfs/squid-asnbl
-- 2.26.2