How to block ICMP Timestamp Requests

RE: How to block ICMP Timestamp Requests

MartinSeener — Thu, 20 Jan 2022 07:28:25 GMT

Hi,
thanks for the feedback. I know that we did not allow ICMP to go through from external, so this was never a "real" issue.
Although I took the time to research and want to quickly describe my findings here for anyone else also looking into this.

- You do not need ICMP even at the Firewall level from external usually
- You may need it in VPNs when using UDP or when your interfaces don't use default MTU of 1500 or provide UDP services
- ICMP Type 8 is Echo Request (Ping), Type 3 is Dest. not reachable among others (defined in (Sub)codes) which you may need

I've now disabled global ICMP altogether and only left all 3 Ping checkboxes enabled, as well as the "Let Traceroute from internal to external". The FW itself it not traceroutable anymore from external.

With this all of my IPSec VPNs still work fine, same for Road-Warrior SSL-VPN and other things.
So this one is fixed for me now. Thanks for your help!

RE: How to block ICMP Timestamp Requests

BAlfson — Wed, 19 Jan 2022 21:15:45 GMT

Martin, if you don't have 'Allow ICMP through Gateway from external networks' selected on the 'ICMP' tab, I don't think you have a problem. If you need some ICMP requests to come through, I prefer to make explicit firewall rules for that.

cheers - Bob

RE: How to block ICMP Timestamp Requests

MartinSeener — Sat, 08 Jan 2022 17:25:50 GMT

Hi,
yes we do. But the issue is not the network behind it nor the "issue" itself. I know this is super minor to fix but I would like to give potential attackers just one less point of information.
I think the "Firewall forward" things are not an issue since most of them only forward from internal to external. The timestamp obtained there is only from the UTM itself.

Maybe we can get a solution here.

RE: How to block ICMP Timestamp Requests

dirkkotte — Sat, 08 Jan 2022 11:35:04 GMT

If you use a private address-range, NATed behind some public IP#s, the problem "...can obtain information about your network..." should not exist.

But i disable all "Firewall forward ..." settings without service problems.