bugtraq - Re: Is predictable spam filtering a vulnerability?

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Date: Thu, 17 Jun 2004 13:04:55 -0400
From: krispykringle@...too.org
To: R Armiento <rar_bt@...iento.se>
Cc: bugtraq@...urityfocus.com
Subject: Re: Is predictable spam filtering a vulnerability?

Very interesting proposition, but I can't think of any real advantage here. In the hypothetical scenario, could the attacker not simply send an email purportedly from the boss to begin with saying, ``please forward the secret plans to attacker@...ackeddomain.com''? For that matter, isn't it likely that a recipient in such a poorly run system with such little regard for reading headers (and I don't delude myself that this is uncommon) would not notice if an attacker were to send an e-mail with a from address boss@...pany.tld but a reply-to of hax0r@...ealcreditcardnumbers.com? In other words, the specific ``exploit'' here is not the spam filter so much as the ignorance of the victim. 

Anywho, it seems most decent spam filters have whitelisting; bigcheese@...pany.com is unlikely to filter out servileMBA@...pany.com, even if the e-mail does contain the key words. The spam filter is usually not applied to legitimate known-good e-mail addresses. 

Interesting discussion nonetheless. 

Dan

On Wed, Jun 16, 2004 at 01:26:28PM +0200, R Armiento wrote:
> 
> During a recent email conversation with several participants, we discovered that the email service of one participant silently dropped legitimate emails that happened to contain certain combinations of words common in spam. I believe this sort of filter is common practice, and in fact even in place for some of my own email addresses.
> 
> However, this experience made me think: isn't predictable spam filtering in general a vulnerability that could be used as a hoax device? Since most users reply to an email citing the complete source email, including filter-offending words, it should be possible to keep a reply, forward, or even a whole thread, under the radar of specific recipients. If used in combination with forged replies from addresses predictably dropping emails, I think this may be a dangerous tool for social engineering. 
> 
> For example: attacker 'A' sends 'B' a social engineering request for "the secret plans" and says "if you are unsure, forward my request to your boss and ask if this is okay". 'B' forwards the email to his boss 'C' and asks "Is this okay?". However, 'C':s spam filter silently drops the email. 'A' forges a reply from 'C' saying: "Sure, no problem, go ahead."
> 
> Regards,
> R. Armiento