mailing list archives
Re: 3Com SuperStack 3 Firewall Content Filter Exploitable Via Telnet
From: "David G. Andersen" <dga () lcs mit edu>
Date: Wed, 5 Mar 2003 16:43:37 -0500
On Tue, Mar 04, 2003 at 11:39:17PM -0000, bit_logic () s-mail com quacked:
The weakness exploited by this vulnerability is that the 3COM filter
apparently does not reassemble fragmented packets before checking a
Taking this trivial exploit a step further, an experienced hacker could
easily write a script or application to automate this entire process,
parsing the source for images and other embedded content where necessary.
This would result in a local copy of the requested site right on the
user's hard disk. In theory, one would only need to break apart key areas
of the HTTP request packet in order to fool the filter, rather than
sending every character individually.
Unfortunately, I do not have the necessary equipment at my disposal to
further test the exploit, although I know for a fact that it works, at
a) Test with a program called 'fragrouter'. What you're describing
are TCP fragments, but it's likely the box doesn't reassemble IP
b) "experienced hacker"? more like "slightly clueful kiddie":
route add default <foo> -mtu 50
Or if you want to be a bit more fancy, just write a proxy
in perl that does a character-by-character write() of the
outbound request. Trivial.
least on firewalls with basic filter configurations. I also have yet to
come up with a successful work-around for this bypass, as it occurs at a
very low level. If anyone has any ideas, I'm all ears. Thanks.
a) use real filtering software (a transparent proxy)
b) don't bother, you can't win against the smart insiders
who want out.
work: dga () lcs mit edu me: dga () pobox com
MIT Laboratory for Computer Science http://www.angio.net/
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