Re: [PATCH 0/5] ipblacklist: IP Address Blacklists

[Tim FitzGeorge <ipfr@tfitzgeorge.me.uk>]

[-- Attachment #1: Type: text/plain, Size: 14430 bytes --]

Hello,

It's my turn to apologise for being slow to respond - I've had a busy
week, but I should have plenty of time over the next couple of weeks.

I've made most of the comments inline, however I think Michael had a
question (which I can't find now) about what happens if someone enables
all the lists.  One thing which would perhaps make this less likely is
that the WUI tags the available lists with whether they're safe or not,
with a footnote that safe means that the list only blocks malicious
traffic.  This won't guarantee that a user won't still try to enable all
the lists, but it should make them realise that they should think first.

I have considered replacing this tag with a risk high/medium/low and
maybe adding a category (invalid/application/scanner/C&C or something
like that), but that may provide too much information and dissuade them
from actually following the links to checkout what the list actually does.

Tim


On 05/12/2019 22:25, Michael Tremer wrote:
> Hello,
> 
>> On 4 Dec 2019, at 17:05, Peter Müller <peter.mueller(a)ipfire.org> wrote:
>>
>> Hello Tim, hello Michael,
>>
>> please see my responses inline...
>>>>>
>>>>> We could periodically update the blacklists on our main mirror (and
>>>>> wait for the network to sync it), make sure it is signed and write
>>>>> a small downloader that fetches, validates and installs them.
>>>>>
>>>>> @All: Thoughts on this?
>>>>
>>>> I think there are a number of points here.
>>>>
>>>> Firstly, from the point of a third party using IPFire, is this really
>>>> solving the privacy disclosure problem?  There's no way round disclosing
>>>> your public IP address to someone you're downloading from; all this does
>>>> is change who that information is being disclosed to.  For the  user
>>>> there's no way of knowing whether the source is more or less protective
>>>> of the user's privacy than the blacklist provider.  Indeed it won't be
>>>> possible to know who the lists are being downloaded from until the
>>>> download starts.
>>>
>>> There is a way: Tor. But that is a totally different story.
>> Well, I see a third option on this: Use the mirror infrastructure we already
>> have. Every IPFire installation discloses its public IP address to one of these
>> servers sooner or later, so we do not disclose additional data if the blacklists
>> were fetched from these.
>>
>> Needless to say, Tor (hidden services) would be better, but that is a different
>> story indeed. :-)
>>>
>>> The point is rather that a forget list can be sent instead of the “real” one.
>> I did not get this. Forget? Forged?? ???
> 
> Yes, I meant to write forged, but auto-correct didn’t let me.
> 
>>>> Secondly, latency; some of the lists are updated every 5 minutes.  While
>>>> I've limited the maximum check rate to hourly, will the updates
>>>> propagate quickly enough.  For reference on my main system the 24
>>>> updates on the CIARMY list made 143 498 changes (additions or
>>>> deletions).  I've seem it do over 200 000.
>> Yes, I observe that behaviour for CINS/CIArmy too. Unfortunately, they do not
>> document a recommended update interval anywhere, so we can only guess.
>>
>> Personally, more static lists seem to be preferable for packet filtering. Highly
>> dynamic ones such as CIArmy should be done via DNSBL queries or something similar
>> - do we really want to have that list here?
> 
> It is not really an option to implement a DNSBL into a packet filter, but I get your point.

One of the 'selling points' for an IP address blacklist is that it can
respond quickly to new threats - or rather new attackers.  While a new
IDS/IPS rule needs time to analyse the threat, generate a rule and check
it, it's easy to add an address to a list.  So, I think the CIArmy list
is potentially useful for protecting home systems etc. with budget
hardware, but I would be very careful about using it for a protecting a
general access website.
> 
>>> How did you come up with the hour? Will it be retried more often if the download was not successful?
>> One hour is the most common interval indeed, but adding some random time might
>> be useful in order to reduce load on the servers providing a blacklist.
> 
> Yes, definitely. Otherwise we will shoot down our mirrors.

When I implemented that section of code, specifying the minimum check
period in hours seemed to provide a convenient way of allowing a check
period covering a wide range, with an hour as the fastest and a week as
the slowest.  I didn't looked at the CIArmy list until much later.  Most
of the lists don't change nearly as much, but the CIArmy list is
described as one that deliberately responds quickly.

>From my production system, for yesterday:

   The following block lists were updated:
      BLOCKLIST_DE: 24 Time(s) - 9341 change(s)
      BOGON_FULL: 1 Time(s) - 10 change(s)
      CIARMY: 24 Time(s) - 159134 change(s)
      DSHIELD: 7 Time(s) - 18 change(s)
      EMERGING_FWRULE: 1 Time(s) - 50 change(s)
      FEODO_AGGRESIVE: 24 Time(s) - 13 change(s)
      SHODAN: 1 Time(s) - 0 change(s)
      SPAMHAUS_DROP: 1 Time(s) - 0 change(s)
      TOR_EXIT: 24 Time(s) - 162 change(s)

and my test system:

   The following block lists were updated:
      ALIENVAULT: 19 Time(s) - 5331 change(s)
      EMERGING_COMPROMISED: 1 Time(s) - 26 change(s)
      TALOS_MALICIOUS: 1 Time(s) - 36 change(s)

That covers most of the lists.  From the WUI, since 1 Dec:

  Blacklist     Entries   pkts  bytes   Last updated
                            in     in
  AUTOBLACKLIST       0    731  51144   Sun Dec 8 18:40:02 2019
  BLOCKLIST_DE    28020    857  46735   Sun Dec 8 18:40:02 2019
  BOGON_FULL        214   5255    189K  Sun Dec 8 16:50:04 2019
  CIARMY          15000  19774    976K  Sun Dec 8 18:04:01 2019
  DSHIELD            20   7992    321K  Sun Dec 8 16:45:13 2019
  EMERGING_FWRULE  1647    197   8383   Fri Dec 6 05:29:07 2019
  FEODO_AGGRESIVE  7169      0      0   Sun Dec 8 18:50:07 2019
  SHODAN             32     34   1530   Sun Dec 8 17:54:09 2019
  SPAMHAUS_DROP     823      0      0   Fri Dec 6 18:22:35 2019
  SPAMHAUS_EDROP    111     82  16433   Thu Dec 5 17:27:09 2019
  TOR_EXIT         1055      0      0   Sun Dec 8 18:31:02 2019

(I've left out the pkts/bytes out fields which were all 0)

Note that where possible I do a HEAD request first and then only
download the list if the modification time has changed since the last
check.  For dynamically generated lists this isn't possible.

If the download isn't successful it just gives up and waits for the next
attempt (apart from the usual retries in the library).  I probably
should to change that so that it only applies the per list minimum
update period in this case (specified in the sources file) rather than
the user specified value as well.

I already use a time offset on the downloads - when it's started from
boot, backup restore or WUI enable, it checks to see if it's installed
in the fcrontab, and if not adds itself at a randomly generated offset
in the hour.

> 
>>>> Third, bandwidth; while the downloads are fairly small (ALIENVAULT is
>>>> the largest at a few MB), there are going to be a lot of them.  How will
>>>> this affect the willingness of people to mirror IPFire?
>> I do not consider this being a problem as we do not generate that much traffic
>> to them. Of course, that depends on the update interval again.
> 
> That depends on your point of view.
> 
> I do not have a problem with this at all in my data center, but there are plenty of people with a volume-based LTE plan or simply a 128 kBit/s connection. It will take a longer time to download the lists for them. We need to mind that.
> 
>>>>
>>>>>
>>>>> Talking about the preference of packet filter and IPS, I prefer to
>>>>> use the latter as well as it gains more insight in what kind of malicious
>>>>> traffic tried to pass a firewall machine. On systems with low resources,
>>>>> this might be problematic and removing load from the IPS can be preferred
>>>>> (make this configurable?!), on others, people might want to have both
>>>>> results.
>>>>>
>>>> You're only going to get one result for a packet whichever way round the
>>>> IP blacklist and IPS are since whichever comes first will drop the
>>>> packet before it reaches the second (well it would be possible to put
>>>> the IP blacklist first and get it to log and mark packets which are then
>>>> dropped after the IPS, but I think that's getting a little complicated.
>>>> In addition I've seen the messages about the trouble marking was
>>>> causing in the QoS).
>>>>
>>>> I think it's a 50/50 choice as to which is more valuable first; it's
>>>> probably going to differ from packet to packet.  For me the possibility
>>>> of reducing the IPS load means I prefer putting the IP blacklist first
>>>>
>>>> It should be fairly easy to add the choice of where to put the IP
>>>> blacklist.  I think it'll have to be in the main firewall script, so
>>>> it'll require a firewall restart, but it's not something that'll be
>>>> changed often.
>>>
>>> I do not think that the user should choose this. If we cannot easily make a decision, how can our users do this? Not saying they are stupid here, we are just giving them something so that they do not have to put the thought and research into things themselves and make their jobs easier.
>> Agreed.
>>
>>>
>>> I think performance matters. And if the IPS comes first, the most likely case would be that we are seeing a SYN packet that is being scanned and after that being dropped by the blacklist. It was pointless to even scan the empty packet (TCP fast open aside). This is only different for other packets with payloads.
>>>
>>> We would protect the IPS from a SYN flooding attack here at least and from scanning more packets unnecessarily.
>> So dropping packets from blacklisted IP addresses/networks before IPS is it, then.
>>>
>>> I do not even think it makes sense to swap the order in the outgoing direction.
>> Me too.
>>
>>>
>>> What IPFire is lacking is a statistical analysis for those logs. Collecting more and more data isn’t helpful from my point of view. Only if you are looking at a very specific thing.This is true, but I am not sure if it makes sense to spend too much work on this.
>> Based on my personal experience, firewall hits observed on a single machine exposed
>> to the internet are interesting, but the overall situation across multiple machines
>> is even more interesting. Very quickly, you'll end on something like a centralised
>> logging server and custom statistical analysis here...
> 
> Probably a project for IPFire 4.0 :)
> 
Or use one of the existing services, like the DSHIELD client
https://dshield.org/howto.html (subject to privacy concerns again).
>>>
>>>>>
>>>>> Personally, I consider Spamhaus DROP/EDROP can be safely enabled by default.
>>>>> I would love to see the bogon ruleset here, too (think about 8chan successor
>>>>> hosted at unallocated RIPE space in Saint Petersburg), but that will likely cause
>>>>> interference if RED does not have a public IP address assigned.
>>>>
>>>> I can add a field to the options file that controls whether a list is
>>>> enabled by default.
>> Thank you. :-)
>>>
>>> To stress the point from above again: We would then share all public IP addresses of all IPFire systems in the world with Spamhaus and who is hosting their infrastructure. That can be considered a threat.
>> This is my only objection against this patchset. Now, what can we do about it?
>> One possibility is to apply the patchset now and implement a custom download
>> source thing later on, or do that before releasing Core Update 139 (or which version
>> the patchset will be to) after we agreed on something.
> 
> I do not see this being merged for 139. But that is not important. We need to get it right first and then release it.
> 
> As far as I know, nobody has tested this, yet.

There are a number of people who have been running an earlier version
which I shared on GitHub.  There were a few early issues, but it seems
to be OK now.

https://forum.ipfire.org/viewtopic.php?f=27&t=21845

This version wasn't integrated into IPFire, so (for example) it inserted
itself into the INPUT IPTables chain rather than having it's chains
created as part of the firewall start-up script.

> 
> I have huge concerns about the automatic blacklist. @Peter: What is your opinion on this?
> 

While I implemented it, I'm aware of its potential to cause problems,
which is why it has to be separately enabled.  It's not caused me any
issues at the default settings (blocks at over 10 packets per hour until
1 hour has passed without seeing packets from the address), but I've not
used it on a site with publicly announced services.  If I was going to
use it on a web site I would want to, at the very minimum, drop the
block period drastically.

On the other hand, it's good at responding quickly.  Usually I see only
1-2% of blocks from the automatic list:

Reason      Count     %  First        Last
CIARMY       2416    45  Dec 6 00:00  Dec 6 23:59
DSHIELD      1353    25  Dec 6 00:00  Dec 6 23:59
INPUT        1294    24  Dec 6 00:00  Dec 6 23:59
AUTOBLACKLIST 122     2  Dec 6 00:20  Dec 6 16:28
BLOCKLIST_DE   89     2  Dec 6 00:20  Dec 6 23:46

and sometimes none at all, but one one occasion it blocked over 8000
packets.  Again I'm aware this is for a home system, which is rather
different than from a Web server.

>> If we do, I will have a look at the licensing stuff (DShield and Spamhaus do not
>> seem to be problematic, as they are hosted on 3rd party servers, too).
> 
> One of them will be, sooner or later. And one is enough I suppose.

DShield (https://dshield.org/api/#threatfeeds) and firehol
(http://iplists.firehol.org/) seem to host copies of most of the lists
as well.
> 
> I do not really want to overthink this - we didn’t do this with clamav for example either. But it probably is a decision to be made by the user what they want to enable and we should not enable anything by default. So no data will be leaked as long as the user does not consent.
> 
> -Michael
> 
>>
>> Thanks, and best regards,
>> Peter Müller
>