[Esd-l] X-Unsent: header as way of recognizing mass mailing worms

John D. Hardin jhardin at impsec.org
Thu Nov 29 07:12:01 PST 2001

On Wed, 28 Nov 2001, Brett Glass wrote:

> I've recently noticed that only transmissions by worms (Badtrans.B
> and Nimda.E) seem to contain an X-Unsent: header. Because it's
> characteristic of several worms, it may be that worm writers are
> re-using code that inserts it. It might be useful to have a local
> recipe that checks for this header and quarantines.


* ^MIME-Version: 
* ^Content-Type:.*multipart/
* ^X-MSMail
* ^X-Unsent: 
| formail -A "X-Content-Security: [$HOST] NOTIFY" \
          -A "X-Content-Security: [$HOST] QUARANTINE" \
          -A "X-Content-Security: [$HOST] REPORT: Trapped mail with
suspicious X-Unsent: header"

I added the MSMail header to try to limit the scope of this a bit, as
the Unsent header may be used legitimately by non-MS mailers.

Again, if you're not using the Sanitizer, substitute your own
quarantine action code in place of the formail call.

 John Hardin KA7OHZ    ICQ#15735746    http://www.impsec.org/~jhardin/
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