Re: Simple DOS attack on FW-1

[taylord () INFOSECURE COM AU (David Taylor)]

On Thu, 29 Jul 1999, Lance Spitzner wrote:

> [snip]
> I've stumbled across a simple Denial of Service attack for
> FW-1, many of you may already be aware of this.  You can
> effectively shutdown FW-1 by filling its connections table.
> This is easily done in about 15 minutes with most port
> scanners.
>
> When FW-1's state connections table is full, it can no longer
> accept any more connections (usually between 25,000-35,000
> connections, depending on your system). You can increase this
> number by increasing kernel memory for the FW-1 module and
> hacking ../lib/table.def) However, a port scanner can build
> that many connections in a manner of minutes.

Lance,

I have seen this also in a Floodgate-1 machine that was positioned outside
the firewall.  Flodgate-1 is Checkpoint's bandwidth management solution
which presumably uses the same state engine.

In this particular instance the firewall that had been deployed was not
capabale of running Floodgate on the same machine so Floodgate had been
deployed on a relatively sacrificial host that was positioned between the
firewall and the Internet router.  As floodgate doesn't do any traffic
filtering, when I portscanned it from an external point the connections
were allowed through to the firewall, where they were dropped without a
NACK/RST/FIN coming back the other way.  The machine consistently died
after a matter of minutes.

Some more graceful error handling on Checkpoint's behalf would probably be
nice.

Regards,
Dave Taylor