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From: rlanguy at (Lan Guy)
Subject: Backdoor not recognized by Kaspersky

One ISP here in Israel, has tried to do something about this.
They block all TCP traffic on port 25 (bi di) except for there own mail 
servers IP
They also have a limited amount of "allowed" IP addresses, such as other 
ISP's but that is it.

Lan Guy
----- Original Message ----- 
From: "Mike Barushok" <>
Cc: <>
Sent: Thursday, March 04, 2004 8:01 AM
Subject: RE: [Full-Disclosure] Backdoor not recognized by Kaspersky

> On Wed, 3 Mar 2004, Larry Seltzer wrote:
>> >>I feel the need to address the problem from an ISP perspective, since 
>> >>the corporate
>> and government and other institutional persective seems to give different 
>> answers. And
>> because the ISP end user problem is still the majority of the reservoir 
>> for viruses (and
>> spam proxy/relay/trojans).
>> I really feel for you guys. As I've argued in another thread, I think 
>> authentication will likely cut this stuff down to a trickle compared to 
>> the current
>> volume. As an ISP, how big a problem would you have with that. An even 
>> better question:
>> Would you have a problem implementing SPF, Caller ID and Domain Keys 
>> (i.e. all 3)? It
>> gets to the same issue of changing practices for your users: at some 
>> point you have to
>> either bounce or segregate mail that doesn't authenticate.
> SMTP auth does not help at all. A virus that delivers email via
> it's own SMTP engine completely bypasses the end users ISP
> server(s). And if the recipient server does not allow incoming
> mail from wherever it is presented from, then incoming mail will
> simply be broken unless there is some sort of SPF. But,
> SPF, caller-ID, and Domain keys all have major
> unsolved issues with forwards, aliases, corporate employees
> checking their work mail and needing to reply through their home
> connection ISP, but with their company 'From: ' address and
> several other common scenarios. Until their is universal
> adoption of some add on to SMTP, nobody can reject all
> non-conforming mail safely.
> All implementations create a much greater load on DNS.
> The real issue is that their is no possible algorithmic solution
> to rejecting email reliably based on any of its source, its
> content, or any combination.
> Then there is the 'rejection' problem. If the mail is not accepted,
> laws prohibit silently discarding it. But any reasonable method
> of attempting to bounce it back to its source after accepting it
> for examination is a completely easily exploited back door the
> spammers and virus writers will use to deliver mail.
> So, the only practical point in the process to decline the mail
> is before the data is sent. A transient error may result only it
> retries every five minutes for the next four days. A permanent
> error may result a cached failure that affects all email for a
> period of time. And the delivery back to the apparent sender
> within the sending ISP is still available as an infection vector.
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter:

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