Last Word On The BlackAttacker.vbs Question
- From: "Jim Harrison" <jim@xxxxxxxxxxxx>
- To: <sb2k@xxxxxxxxxxxxxxx>
- Date: Tue, 21 Sep 2004 16:56:02 -0700
(if you want me to see your reply from sbs2k@xxxxxxxxx, please 'r' me)
Hi all,
It's come to my attention that the once-proud BlockAttacker script is once
again the subject of deep discussion.
This script has been pulled from isatools.org (it never was on isaserver.org)
and it will not reappear on that site so long as I own
/ run it.
It is no longer supported by me, Microsoft or anyone cooperatively associated
with either one of us.
This subject (and related script) has been abused, misused and misunderstood
for far too long.
It stops here and now.
Contrary to what you might have heard, this script was never intended for
anything more than an example of how to use environment
variables in ISA 2000 alert actions. As with any good deed, it has not gone
unpunished.
If you are using it for automatic "deny" policy creation, consider this:
1 - with the notable exception of SMTP Filter alerts (you're not using it
there, are you? That would be silly in the extreme...),
if ISA generated an alert based on the traffic from the remote host, that
traffic was also blocked. Adding a rule to block traffic
that is already silently dropped is a waste of processor time (redundantly
repetitive).
2 - Every time this script creates a new packet filter for a presumed "attack
on your property":
a - it takes CPU time to create, update and save the changes; if your
script is creating rules as fast as someone can DoS your
ISA with spoofed packets, then your firewall quickly becomes a network brick.
b - you complicate the ISA policy set. Every rule in the ISA engine takes
processing time. The fewer rules you have, the
faster your ISA can process the traffic
IOW, leave this monkey-script in place long enough and your ISA will crawl
to a halt.
3 - ISA can generate "attack" alerts on any number of packets that ISA deems to
be "out of context". Most notably, these include
(but are not limited to):
1 - "late" packets; these are response packets arriving from a server
outside of the time ISA considers traffic from this host
to be "valid".
You'll usually see these when internal clients drop their session
before the server finishes the response stream.
99% of the time, ISA will report these as "scans" and drop them
2 - DHCP traffic from your ISP; even if you use static IPs, it's very
likely that someone in your broadcast subnet uses dynamic
IPs.
Will your ISA see these? You betcha.
Will it trigger on them? Maybe; it depends on your configuration and
how many alerts you've enabled.
3 - Real attacks using spoofed source IPs; here's the real danger.
All it takes is one script-kiddie to slam your ISA with spoofed packets
from the entire IP v4 space and your ISA will no
longer be functional in the Internet. If you think this is hard to do, you're
fooling yourself.
4 - There has been some discussion regarding:
a - the value of blocking traffic from 127.0.0.1 and how your ISA will
lie bleeding to death on the floor from the "circle
of death" resulting from such an attack. The fact is, while ISA is properly
configured in Firewall or Integrated mode, this
"attack" profile a non-issue. ISA 2000 in Cache mode has no such
self-protection, so you should use a properly-configured
packet-filtering router.
b - the potential for blocking traffic from your own ISA server is less
than zero. Any traffic seen at the external
interface with a source IP of 127.0.0.1 is a spoof packet, period. End of
discussion. You should get mad at your ISP for allowing
this to reach you, not some "think for me" script for not having a "whitelist".
As always, I'm interested in feedback, but here is the final word:
"BlockAttacker.vbs is not a supported tool for any Microsoft product in this,
or any other lifetime in which I may be a member."
Anyone who wants to offer intelligent discussion on the subject will be heard,
and maybe even responded to in kind (of).
Anyone who wants to cry "foul" (no; wait, that's "spooooon!") will be
courteously (or not) ignored.
Jim Harrison
MCP(NT4, W2K), A+, Network+, PCG
http://isaserver.org/Jim_Harrison/
http://isatools.org
Read the help / books / articles!
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