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Message-ID: <20040304123314.TDIK411419.fep03-mail.bloor.is.net.cable.rogers.com@BillDell> From: full-disclosure at royds.net (Bill Royds) Subject: E-mail spoofing countermeasures (Was: Backdoor not recognized by Kaspersky) Having a MS record would not eliminate spam coming from users validated on the sending server, but it would identify the server that it comes from as "knowing" the sender name. Compromised client boxes would need to use the ISP mail server to send mail, rather than spewing it directly, since the servers allowed on the MS entry for that domain would not include the client host. Either the ISP owing the server blocks spam spew or that ISP gets a blackhole block that would be very effective. Yesterday I inspected the spam I had in my spam bucket for kinds of actual senders (last sender on Received header for my ISP). Of 11 spam messages in the last hour, 9 were from compromised machines sending directly. If they had to send this stuff through their ISP (comcast, telstra, swbell etc.), they would be blocked fairly quickly. The envelope from address was often Yahoo, so the ISP would block on this as well. Requiring MS entries would not block spam or viruses immediately but would help make RBL lists more effective and prosecution of spammers easier (easier to trace a registered user of an ISP). -----Original Message----- From: full-disclosure-admin@...ts.netsys.com [mailto:full-disclosure-admin@...ts.netsys.com] On Behalf Of Nick FitzGerald Sent: March 4, 2004 3:00 AM To: full-disclosure@...ts.netsys.com Subject: RE: [Full-Disclosure] E-mail spoofing countermeasures (Was: Backdoor not recognized by Kaspersky) "Bill Royds" <broyds@...ers.com> wrote: <<snippage>> > Using authenticated SMTP, this would still allow a different return > address in headers since envelope from would be user who authenticated to > SMTP server. But it would prevent spoofed email (although spam would still > arrive, it could be tied to actual sender, allowing things like CAN-SPAM to > work). Wrong. It would, at best, identify the sending _machine_, not the "actual sender". There is far too much prior art in the Windows malware armory to not be aware of how easily an agent program on a "compromised" Windows box can steal whatever configuration and authentication data it may need to "properly" send mail "just like" the user's preferred MUA. Just because, of late, spam and mass-mailing viruses have used randomized From: and SMTP envelope FROM addresses does not mean thay have to continue to do so, nor that not doing so will necessarily be less effective for them... These are important considerations to not overlook despite the fact that the SPF, etc pushers make a habit of ignoring such. Further, several IRC bot-nets in tens-of-thousands of active bots size range have already been found and there are probably several million such compromised mnachiens out there waiting for the fateful order to "wake up" and answer the call of their "master". SMTP "sender authentication" is a far less trivial problem to solve that the SPF, aller-ID, etc folk would have you believe (and, of course, they don't like us pointing out that their preferred "solutions" are already doomed to failure). -- Nick FitzGerald Computer Virus Consulting Ltd. Ph/FAX: +64 3 3529854 _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.netsys.com/full-disclosure-charter.html
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