RE: Relaying question

  • From: "KEN MORRIS" <KMORRIS@xxxxxxx>
  • To: "[ExchangeList]" <exchangelist@xxxxxxxxxxxxx>
  • Date: Fri, 26 Sep 2003 13:33:08 -0400

Chris,
I have been having the same problems.... But unchecking that has not stopped
our users from relaying. The problem being once they have a user/pswd (which
I think is my case), they can still get in and set up more spamming anytime.
I have had to freeze queues and delete the spam messages in order to try to
keep it clear.
So while this may appear as a fix, it will depend on how malicious they want
to be.
Ken

-----Original Message-----
From: Allen, Chris [mailto:CAllen@xxxxxxxxxxxxxxxx]
Sent: Friday, September 26, 2003 1:25 PM
To: [ExchangeList]
Subject: [exchangelist] RE: Relaying question


http://www.MSExchange.org/


According to Microsoft, my exchange is secure. We are not an open relay and
in theory we should have no worries. However, the type of relaying going on
here is malicious. It is a brute force attack on our user-base and not a
simple IP spoof. The relay options in system manager are to allow all relay
traffic except for the following. Then we have added the internal IP of our
firewall as the exception since it nats all traffic including SMTP.
Therefore, if someone wanted to relay, their email would appear to be from
the internal NIC of the firewall and would be stopped. However, the checkbox
at the bottom of this same screen says, "Allow all computers which
successfully authenticate to relay, regardless of the list above". Therefore,
when they manage to get a user/password that works, it doesn't matter where
it comes from, they will get relayed. What will happen if I uncheck this box?
Will true internal users still be able to relay? Will external relay be
stopped using the smtp/Auth method? These are the questions I cannot find
answers to. Any help would be appreciated. Thanks.

 

-----Original Message-----
From: Mulnick, Al [mailto:Al.Mulnick@xxxxxxxxxx] 
Sent: Friday, September 26, 2003 10:20 AM
To: [ExchangeList]
Subject: [exchangelist] RE: Relaying question

 

http://www.MSExchange.org/

Have you considered having a look at the information on this subject at
www.microsoft.com/security ?

 

There are some articles that discuss how to secure your server that also
talks about the trade-offs that go with it.  Although Tom's idea of fun is a
little skewed ;) you can hurt yourself if you make the changes without a full
understanding of what you are doing and what it's effects will be.  

 

 

ajm

-----Original Message-----
From: Allen, Chris [mailto:CAllen@xxxxxxxxxxxxxxxx] 
Sent: Friday, September 26, 2003 9:54 AM
To: [ExchangeList]
Subject: [exchangelist] RE: Relaying question

http://www.MSExchange.org/

The problem is, I need to allow relay internally. I have various custom apps
that the users need to email a client upon completion of a workorder. They
each do over 500 a day and automation is the only way to do this effectively.
So, if I shut off the checkbox in question, will the internal IPs still be
able to relay?

 

-----Original Message-----
From: Thomas W Shinder [mailto:tshinder@xxxxxxxxxxxxxxxxxx] 
Sent: Friday, September 26, 2003 9:50 AM
To: [ExchangeList]
Subject: [exchangelist] RE: Relaying question

 

http://www.MSExchange.org/

Hi Chris,

 

Yes. If you don't allow relay, then the server will not relay. You can also
do other things like prevent the machine from resolving Internet host names
(just for fun).

 

HTH,

Tom

 

Thomas W Shinder

 <http://www.isaserver.org/shinder> www.isaserver.org/shinder 

ISA Server and Beyond: http://tinyurl.com/1jq1

Configuring ISA Server:  <http://tinyurl.com/1llp> http://tinyurl.com/1llp

 

-----Original Message-----
From: Allen, Chris [mailto:CAllen@xxxxxxxxxxxxxxxx] 
Sent: Friday, September 26, 2003 8:34 AM
To: [ExchangeList]
Subject: [exchangelist] Relaying question

http://www.MSExchange.org/

 

Per SpamCop and SpamHaus, "Spammers are taking advantage of weak passwords on
systems using smtp/auth and brute force finding name/password combinations
that work and then sending spam thru these servers. There are various
characteristic footprints for this and one of them is the use of a "from"
address of the format bluestallnn@some legit ISP and the "nn" iterates in
each successive spam.

 

bluestelllf@xxxxxxx

bluestellpg@xxxxxxxxxxx

bluestelluf@xxxxxxxxx "

 

My question is this, if I uncheck "Allow all computers which successfully
authenticate to relay, regardless of the list above", will this effectively
stop brute force attacks on weak passwords as far as exchange is concerned
and what will this break?

 

I am also taking measure by blocking their entire block of IPs. The ranges
are as follows:

 

211.158.32.0/20

211.158.48.0/21

211.158.80.0/20

219.153.144.0/20

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