Hi Niels.
It's a valid concern on some firewalls.
Many firewalls don't do any application level checks, they just check the
port. If you're not using something like a Netscreen, or a Checkpoint
firewall, or another firewall that does application level filtering, your
hacker will be able to gain access through any port that is open.
I'm sure someone will be able to tell you more firewalls which can do
application level filtering, or correct me if i'm wrong.
;)
Max Ashton
On Thursday 26 January 2006 20:27, Niels Taylor wrote:
Hello list, I hope this question is not too "newbie," and I am sure if it
is I will find out quickly. I am interested in ways an attacker could
circumvent outbound FTP restrictions on a FW. I have researched this a bit
but the information I am seeing is ambiguous, so I thought I'd take it
straight to the experts.
If a remote attacker gains command line access to a server (I am concerned
about a Microsoft 2000 SQL server specifically) that is behind a firewall,
and outbound FTP had been disabled at the FW, could the attacker use the MS
FTP "Open" command to specify a different, unrestricted outbound port (e.g
80 or 443) to transfer files, (assuming of course that his FTP server is
configured to listen on this port). Is this a viable scenario, and if not,
could he send files via another method? This question assumes no outbound
application layer inspection at the FW, so that it isn't able to see FTP
traffic on port 23, or 80, for instance.
Thank you for your help.
Niels Taylor
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