[Full-Disclosure] E-mail spoofing countermeasures (Was: Backdoor not recognized by Kaspersky)

["Lachniet, Mark" <mlachniet@xxxxxxxxxxxxxx>]

RE:  Accepting mail from spoofed hosts

This is really a very simple idea, and a hundred people smarter than me
must have thought of it, but I have to wonder if yet another layer of
e-mail security might not be in order as well - don't all email systems
have a unique message ID on them?  Sendmail certainly does.  Why not set
up some kind of system where the recipient email server does a kind of
challenge-response to the originating domain, kind of like IDENT.

Here the recipient is the recipient.com mail server, and has a MX record
for recipient.com and sender is the sender.com mail server and has a MX
record for sender.com

Recipient  --->  Sender  : I got a message from joe@xxxxxxxxxx - is it a
legit user?
Sender  --->  Recipient  : Yes, that's one of my users
Recipient  --->  Sender  : Do you have a record of email ID QF2341ASZF
for this user?
Sender  --->  Recipient  : Yes, that user sent the email
Recipient  --->  Sender  : Thanks, party on Wayne (email accepted)
Sender  --->  Recipient  : Party on Garth (super, thanks for asking)

You might combine the first two dialogs in one, ie, "do you have message
ID QF2341ASZF from user joe@xxxxxxxxxx" and provide non-descriptive
error messages, so people couldn't easily harvest email addresses ala
SMTP VRFY.

Of course on the down side, you'd have to use your email server, with
legit MX record as your smart host for all users (may be a hassle for
home offices and POP clients, maybe requiring outgoing SMTP auth, but
that's easy right?)

Add to that a good RBL system, and you could cut down a boatload of
spam.

Mark Lachniet

-----Original Message-----
From: Aditya, ALD [Aditya Lalit Deshmukh]
[mailto:aditya.deshmukh@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx] 
Sent: Wednesday, March 03, 2004 1:06 PM
To: Bart.Lansing@xxxxxxxxx
Cc: full-disclosure@xxxxxxxxxxxxxxxx;
full-disclosure-admin@xxxxxxxxxxxxxxxx
Subject: RE: [Full-Disclosure] Backdoor not recognized by Kaspersky

> The zip's contents can
> be seen without the password, just not unpacked...no cracking it
required.

now winrar has a option to encrypt file names with a password, me thinks
pkzip with the 64 bit compression also has that feature... how are we
going to deal with this ? by stopping all the compressed mail at the
email gateway ?

we do have one solutions: all the mail headers are spoofed so just stop
accepting mail from spoofed host, this should solve your spam problem
also

> You should be blocking executables by policy anyway, yes?

that is always being done by the all the people in this day and age,
only now we seem to forget to add the compressed file format that are
encrypted so that their file contects cannot be seen ?

-aditya 




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