https://issues.apache.org/SpamAssassin/show_bug.cgi?id=4469





--- Comment #16 from Mark Martinec <[email protected]>  2009-08-21 09:27:43 
PST ---
> Mark: how do you deal with the danger of phishers inserting fake
> 'X-Amavis-MessageSize: mmmmm, TRUNCATED to nnnnn' headers in their templates
> to avoid DKIM checks?  (you could avoid it by ensuring the header appears at
> the start of the message, before any trusted+internal Received hdrs, if you're
> not already doing that.)

I already do that. The header field is always prepended to a message when
passing it to SA, and the rule (as suggested above) only checks for the
*first* occurrence of such header field:

header __TRUNCATED X-Amavis-MessageSize =~ m{\A[^\n]*TRUNCATED}m

> Perhaps we should "standardize" an official TRUNCATED header name.

Wouldn't hurt.

> There is also the issue that HTML spam can be easily concocted that contains
> an innocent-looking body for the first 512KB, then includes 3KB of spam
> payload which uses CSS to hide the innocent text and display only the payload.
> But I guess that may not be a showstopper.  Certainly not as bad as spam
> getting past, unscanned. ;)

I'm aware of this, but for the time being this isn't being
exploited. It's certainly no worse than not checking at all.

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