Everyone,
Does anyone have a reference point for commonly blocked ports?
We have a list, some reactive and some proactive, however we need to remove ports that are no longer a threat and add new ones as they are published.
Thanks
luke
All ports that are open are threats, at least potentially. What you *should*
be doing is:
a) When you block a new port due to a current exploit, log the fact.
b) Work with customers/users to make sure they're patched, and that new machines
are patched before they go live.
c) When probing for the port stops (which it never does), or some sufficient
number of downstream boxes are patched and safe, remove the block.
Either that, or block the world, and open ports on request.
Remember - *you* are the only one on this list who really knows if a given
port is a threat anymore....
(And that's totally skipping all the noise about corporate firewalls versus ISP
firewalls and different expectations regarding security/transparency...)
Not quite looking for tips to manage my network and ACL's or if should or should not be blocking, more looking for actual ports that other ISP's are blocking and why.
For example:
port 5 worm 2.5
port 67 virus 8.2
Probably not exactly what you are looking for, but Conseal (now 8signs) has a
listing of commonly used trojan ports at:
http://www.consealfirewall.com/firewall/trojan_ports.cfm
Not quite looking for tips to manage my network and ACL's or if should or
should not be blocking, more looking for actual ports that other ISP's are
blocking and why.
seems to me this is the wrong question... a default security "posture" (network or system, isp or enterprise or any type of entity) should be: "if it's not explicitly allowed, it's denied."
don't look for specific ports to block. lock down everything, both *egress* (arguably as important as ingress, and typically completely ignored) and ingress, and start opening only specific ports that are absolutely necessary. yes, it's a lot more work to do this but it's a lot safer.
many worm/trojan infections happen because egress is completely open, and "permit tcp any any established" is the first line in the ingress acl.
-b
There is only one port worth blocking:
Block port 80 (http)
All other ports might be in use for redirected ssh, telnet, ftp, ...
Blocking port 80 will keep windows people from accidently clicking nonsense.
Kind regards,
Peter and Karin Dambier
Luke Parrish wrote:
Depends where you will put your ACL too,
we have this on our Ingress from the internet
10 deny ip 127.0.0.0 0.255.255.255 any (118 matches)
20 deny ip 10.0.0.0 0.255.255.255 any (23297 matches)
30 deny ip 172.16.0.0 0.15.255.255 any (8 matches)
40 deny ip 192.168.0.0 0.0.255.255 any (19 matches)
50 deny tcp any any eq 135 (6750649 matches)
60 deny udp any any eq 135 (20275 matches)
70 deny tcp any any eq 445 (18420302 matches)
80 deny udp any any eq 1026 (3481591 matches)
90 deny ip x.x.x.x 0.0.0.255 any
where x.x.x.x is your IPs
and you could add bogons
But of course you might not want to block some of those as some home customers could use them to connect back to their intranet, but those should use tunnels IMHO.
Kim Onnel wrote:
80 deny udp any any eq 1026 (3481591 matches)
This will make one out of 4000 of your udp "sessions" to fail with older stacks which have high ports from 1024 to ~5000.
Pete
Luke Parrish wrote:
Not quite looking for tips to manage my network and ACL's or if should
or should not be blocking, more looking for actual ports that other
ISP's are blocking and why.For example:
port 5 worm 2.5
port 67 virus 8.2
www.dshield.org, www.mynetwatchman.org ?
/mjt
Michael Tokarev wrote:
www.dshield.org, www.mynetwatchman.org ?
That should be: www.mynetwatchman.COM 
Both are excellent resources.
-Jim P.
If you don't already know, it might be worth looking at a detailed
breakdown of the source ports hitting that rule. It may be blocking
a good amount of DNS and NTP traffic for instance. If that is the
case, what you may find an acceptable alternative is to preface it
with rules like this so at at least your recursive DNS servers will
not have to maintain the recursive query in memory until it times out
and your time servers don't miss a poll:
permit udp any eq 53 host [recursive-dns-server-address] eq 1026
permit udp any eq 123 host [time-server-address] eq 1026
If a larger population of hosts are doing DNS then you'll have to
decide whether or how to open it further or accept occasional
failures.
Note, in my experience, many of the Windows-based worms tend to use
a source port > 1023, so while this opens an even bigger hole, you
could allow through all src ports < 1024, which should create less
breakage. You filtering policy and security stance may not permit
the trade-off of course, but it's another option I've seen used.
John