[Snort-users] fbidsmate and watchguard firebox
jeff at ...950...
Thu Sep 4 15:42:07 EDT 2003
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well stated. I just wanted to clarify.
On Thursday, September 4, 2003, at 02:24 PM, Matt Kettler wrote:
> At 04:08 PM 9/4/2003 -0400, Hamilton, Robert wrote:
>> Any way to directly call fbidsmate from snort alert rules?
> Directly from snort there is no way to call *any* firewall tool.
> Fundamentally out of the box snort is an IDS and only an IDS. It has
> no support for reconfiguring any firewalls of any sort. No support for
> IpTables, IPF, cisco, watchguard, or any other kind of firewall is
> It does have a *very* limited ability to attempt to kill offensive
> connections using flexresp, but this doesn't reconfigure a firewall..
> "react:block" just causes flexresp to generate some tcp reset packets
> or icmp unreachable messages. It is however not reliable when racing
> against an educated attacker (If the attacker knows flexresp is going
> to issue a reset in response to an attack, they can attempt to advance
> the sequence number before flexresp can respond. Flexresp is being
> improved to help avoid this, but it still fundamentally boils down to
> a race where flexresp has the speed advantage, but the attacker has
> the advantage of knowing when the race will start and can be prepared
> in advance. .)
The react keyword implements HTTP (application layer) blocking by
returning HTTP data to the client browser. The resp keyword performs
the active response that you're describing above.
Flexresp2, released yesterday, uses a brute force approach for
desynchronizing TCP connections. The biggest hinderance in this race
is TCP stream reassembly. Essentially, TCP segments are coalesced
before the detection plugins even get them, making active response
While an attacker can try to advance their sequence numbers outside the
range used by flexresp2, they can't do this easily. This sort of
attack would require some sort of event-based logic to track the state
of the connection used for the attack and would have to "cook" ethernet
frames and avoid the actual TCP/IP stack.
Flexresp2 already does this :) It makes a few assumptions on the rate
of ACK number consumption and attempts to send a TCP reset packet with
an ACK number that lands within the acceptable range of sequence
numbers. By default it sends three of these to the receiving TCP.
> It's only add-ons such as snortsam which extend firewall modification
> capability, bringing snort more into the realm of IPS type
> functionality than IDS functionality.
Snort_inline provides the sort of functionality being requested. (as
you mention below).
> And really, this separation into different add-on tools allows snort
> to be as flexible as possible without becoming insanely bloated. Snort
> by itself focuses on being a good IDS, and projects like snortsam and
> inline-snort focus on firewall manipulation.
http://cerberus.sourcefire.com/~jeff (gpg key available)
"Great spirits have always encountered violent opposition from
mediocre minds." - Albert Einstein
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