Block an IP Address Trying to Brute Force into VPN

[Matthew Martin]

Hello,

I noticed last week this IP Address attempting to VPN into our system. I noticed in our ISE LiveLogs this IP Address attempting to connect 100s of times a minute.

In an attempt to stop this address from even attempting the VPN, I looked on our ASA.
ASDM > Configuration > Firewall > Access Rules.

On the outside interface there was already the top rule configured to Deny access to a Network Object Group that just has a list of IP Addresses. So I added this questionable IP Address to that Object Group. However, I am still seeing the IP Address in ISE attempting to VPN in.

Any ideas why this address is still able to attempt auth, even though it should be getting denied before it even gets that far?

ASA Access Rule:
The IP address in question has been added to this "denied_access" group.

ISE LiveLogs:

Is adding this IP Address to the Access Rules applied to the outside interface, not the correct place to prevent this IP Address from even attempting a VPN connection?

Thanks in Advance,
Matt

[Rob Ingram · Accepted solution]

@Matthew Martin a normal ACL on the ASA controls traffic "through" the ASA, not "to" one of the ASA's interfaces. You need can use a control plane ACL to restrict this IP address.

Create a normal ACL to deny the source IP address, then assign the ACL to the outside interface and append control-plane to the end. Example:-

access-group CPLANE in interface OUTSIDE control-plane

This control plane ACL won't interfere with the normal traffic through the ASA.

[Matthew Martin]

Thanks Rob, I created a network object-group and inserted a couple more IPs that I noticed in ISE, which was hitting our outside interface frequently and attempting to auth through VPN. I then created the deny ACL and applied the network object-group to it. And finally, ran the access-group command.

!
object-group network BLACKLIST_OUTSIDE
 description Blacklisted IP Addresses for the Outside interface
 network-object host xxx.xxx.xxx.xxx
 network-object host yyy.yyy.yyy.yyy
 network-object host zzz.zzz.zzz.zzz
!
!
access-list CPLANE_OUTSIDE extended deny ip object-group BLACKLIST_OUTSIDE any log
!
!
access-group CPLANE_OUTSIDE in interface outside control-plane
!

 So far so good. It's been about an hour since I applied the commands above and I have not seen anymore VPN attempts from those addresses in our ISE server's LiveLogs.

Thanks for the assistance, much appreciated!

[MHM Cisco World]

can you more elaborate ?