Preventing spoofed internal e-mail

Published: 2007-06-26
Last Updated: 2007-06-26 01:16:20 UTC
by Johannes Ullrich (Version: 1)
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Nick submitted a nice piece of malware we are currently looking at. The malware itself includes a nice rootkit that doesn't appear to be detected with common rootkit tools. However, in my opinion, the delivery method was noteworthy. It used a spoofed internal sender. This made me wonder what's the best way to block e-mail that comes from outside mail servers, but claims an internal "From:" header.

My first guess would be that this is a great reason to enable SPF. Will this work?  I am assuming that it is a standard policy to require employees to use a VPN connection or "something like that" to send e-mail using an internal mail server.

Any other ideas?

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