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.
While the stock ftp.exe that is on my Win2K box does not provide for
changing the port used, that doesn't prevent other applications from
doing so. Since it is a common security practice to run such things as
sshd on non-standard ports, there's every reason for a trojan, worm, or
virus to use the same technique to avoid the usual roadblocks or
detection techniques based on port.
And, don't think for a moment that malware would be restricted to ftp
for transfer of files. Any good programmer could choose among the many
suitable protocols for communicating, or even invent one. Then, it
would be a simple matter for the infected host to just keep trying
outbound ports until it finds an opening. For example, how many
firewall configurations block a connection from a high port on the
originating host to port 80 on a distant server? Very few, right?
Over and above all the information security hardware, sometimes
detection simply boils down to a technique that beat cops have used
since the beginnings of professional security, and that is "suspicious
behavior".
And, regarding your SQL server on the internal net; you might consider
blocking ALL traffic from it to the outside world. Vulnerable,
high-value systems should be tightly insulated, firewalled, and proxied
well away from any threat.
I hope this answers your question.
Good luck.
Mark Stingley
--
Excellence in InfoSec and Linux
http://www.altsec.info
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