[Snort-users] react: block not working

Micheal.Cottingham micheal.cottingham at ...11154...
Fri Feb 6 12:14:00 EST 2004

At 09:25 AM 2/6/2004, Micheal.Cottingham wrote:
>As per the subject, react: block does not seem to be working. ACID is 
>still picking up the alerts even though react: block is set. An example
>rule is:
>alert icmp $EXTERNAL_NET any -> $HOME_NET any (msg: "ICMP Large ICMP 
>Packet"; dsize: > 800; react: block; reference: arachnids, 246;
>side: 499; rev: 3 classtype: bad-unknown;)

>You probably need to get a MUCH better understanding of what react:block 
>does before you use it further.


>1) react:block is NOT a firewall
>2) react:block will NOT stop subsequent attempts
>3) react:block will not prevent the current packet alerted on from entering 
>your network.
>4) react:block does nothing useful when used on ICMP packets.

>React:block _does_ however _attempt_ to reset a connection by using the 
>flexresp system. This, if successful, prevents any more data in the given 
>session from entering your network.... ICMP messages are sessionless, and 
>there's little of any value that can be done to them after-the-fact.

Figures I missed something. heh. We do have two Cisco PIX, one primary, one failover for this site of our institution. However, for various 
reasons, we need IDS/IPS. I realize we can make the firewall do some of the stuff for us. However, there have been some things that the 
firewall would not be able to do.

At 09:25 AM 2/6/2004, Micheal.Cottingham wrote:
>am doing this for other things such as MSSQL Propogation Attempt, NMAP 
>Ping, etc. I especially want to block ICMP Large Packet as the
>TTL's have been modified, and the payload is a bit screwy to say the 
>least. MSSQL Propogation Attempt is another big one on my list. I am in a
>pure windows environment and my boss is not favorable of *nix, so hogwash 
>is out of the question I'm afraid. snort-inline is also just *nix if I
>am not mistaken, is it not? I am using Snort 2.1. Any help would be 
>greatly appreciated

>Whoops, sorry, missed the second half...

>Really, since Windows doesn't come with a flexible scriptable firewall, 
>there's little that you can do directly on a windows box itself.

>If you must stick to windows-only you can buy a copy of CheckPoint FW/1 for 
>your Windows box and use snortsam.

Believe me, if I had my way, we'd be on at least some *nix machines, if not all.

>Although for the money I'd recommend not buying FW/1 and getting a separate 
>firewall box and have snortsam command that. For the price of FW/1 you 
>should be able to buy a Cisco PIX or Watchguard firebox. From what I read 
>on the net, Checkpoint can be pretty pricey.

Yeah, as I said above, we do have two Cisco PIX firewalls, but for various reasons, we need IDS/IPS.

>Snortsam can handle a variety of firewalls and can run with snort on a 
>windows box :

Thank you. I'll take a look at this. Will this provide what we want? As I mentioned before, we want to block/drop ICMP, UDP, and TCP packets.

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