Thomas kinghorn wrote:
> Good afternoon all.
>
> Please forgive me if I am asking a stupid question.
>
> My server is currently being used, via a compromised account, to send junk
> to various freemail accounts.
>
> An extract of the message looks like:
>
> 208P Received: from [125.76.228.201] (helo=User)
> by smtp01.gennex.co.za with esmtpa (Exim 4.69)
> id 1MB4KF-000Nhu-W3 by authid <[email protected]> with
> login_authenticator; Mon, 01 Jun 2009 12:01:36 +0200
> 041R Reply-To: <[email protected]>
> 056F From: "Mr. Song Lile"<[email protected]>
> 228 Subject: Good Day,I am LILE, I work with the Hangs bank,I need your
> assistance in effecting a transaction worth $19.5m I intend to give 30% of
> the total funds as compensation for your assistance. Full names,Private
> phone number
>
> If I were to create a list of compromised accounts (until we can get the
> users to use decent passwords), how would I go about this
> as everything I have tried thus far has failed.
It should not be as easy for an attack to suceed as you claim - your
authentication may have holes in it.
Rather than parse a 'new' list, it is *FAR* easier to do a forced change to the
compromised user's password....
ELSE set a flag that it is invalid-until-changed for smtp (optionally POP /
IMAP).
As authentication would fail at login, no new logic would be required.
Go do that NOW before your entire user community finds themselves on a
blacklisted server......
..waiting ...
Presume you have gone off and done so by now....
Now then ...
Show us what you have for:
daemon_smtp_ports
tls_advertise_hosts
auth_advertise_hosts
The entirely of:
- Your acl's as 'mapped' from:
acl_smtp_connect =
acl_smtp_rcpt =
acl_smtp_auth = (if used. ELSE your authenticator acl's)
Any clauses elsewhere that include an authenticated conditional.
>
> I was thinking of something along these lines:
>
> # ACL MACRO
>
> # authenticated id {$authenticated_id}
> ACL_C_AUTHID = acl_c_authid
>
>
> # Connect phase #
> acl_check_connect:
>
> #Set ACL for AUTHID
> warn
> condition = ${if
> match{$authenticated_id}{lsearch;/usr/local/etc/exim/reject/rejected_authid}}
> set ACL_C_AUTHID = Yes
>
>
> # Compromised Accounts
> deny
> message = '$authenticated_sender' classified as compromised -
> Please change your account password
> condition = ${if eq {$ACL_C_AUTHID}{Yes}}
> logwrite = :main: Compromised Account: $authenticated_sender
>
> The list rejected_authid would contains the email addresses of the
> compromised accounts.
>
> Many thanks in advance for your assistance.
>
> regards
>
> Tom
> (exim wannabe)
'going forward' ....
- Neither Exim, nor whatever you are using for POP/IMAP absolutely require UID
be in the form of a <$local_p...@$domain>.
Clearly, so doing 'publishes' HALF the information required for login as a
'free
gift' to the world at large.
All that remains is finding, guessing, or brute-forcing the PWD.
So....
- Decouple the login UID from the email address or anything ELSE published.
- Make BOTH UID and PWD *LONGER* than 16 characters. Even a 17 or 18 character
minimum is beyond what most attackers will try.
- Make sure to handle all that *inside* an SSL or TLS session, on port 587, not
25, and DO NOT allow fallback to unencrypted.
- 'system' or 'shell' login UID and email addresses do not need to be related,
and IMNSHO, should NEVER be. 'Virtualize' and keep those worlds *separate*.
If a compromised mail account is bad news, a compromised shell login is doubly
so.
Bill
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