Question

Using wireshark to detect spam

Asked by: rickBergami

Hello,
 A client of mine keeps getting put on the spam blacklist.  The exchange server is not set up for open relay so I suspect someone on the network is sending out the spam.  I read on here to install wireshark. I installed this on exchange server but does anyone know a quick tutorial on how to detect this?  I did see something smtp related coming from  216.35.161.28 which when I did a whois belongs to coolsavings.  Does this mean they are connecting directly to my machine?  Thanks

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Asked On
2008-04-26 at 17:51:27ID23356456
Topics

Email Servers

,

Exchange Email Server

,

Simple Mail Transfer Protocol (SMTP)

Participating Experts
2
Points
500
Comments
6

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Answers

 

by: perkins328Posted on 2008-04-26 at 19:14:49ID: 21447782

Sounds like if you think a Machine sending spam, I would look for BOTS running very popular, If the client has a Firewall, Limit the mailserver only the ability to send from port 25. Log the firewall traffic, this will also help. Monitor the Queue in Exchange to see what mail is being Queued

 

by: marce_litoPosted on 2008-04-26 at 22:13:43ID: 21448238

You should install Wireshark on the network's internet gateway (hopefully a Linux box) and then you should be able to see all traffic coming from or going to the internet... if you cannot install wireshark on the network's internet gateway (because it's a router or your client does not want you to install anything intç there, or any other reason) you could make a tap by connecting a small network hub (not a switch, unless it's capable of replicating all traffic on one port) between the gateway and the net, and then plugging a computer with wireshark in that hub

a "port 25" command in the capture filter will help you to not analyze all traffic but only smtp

legal outgoing smtp traffic should only originate from your exchange server, and not from any other machine in the net..

 

by: rickBergamiPosted on 2008-05-12 at 10:04:10ID: 21548661

Thanks marce.  Is there a way a newbie like me can figure out what I am looking for? How can I tell if a computer on network has a virus and is sending spam or if someone is connecting to my computer some how to send it?  Or even if the server itself is sending spam?  Thanks

 

by: marce_litoPosted on 2008-05-12 at 14:53:21ID: 21550817

Well, if you made your capture with the "port 25" command and the tap was made on the internet gateway (i.e. not on the exchange server), you'll only need to look for internal ip addresses... they shouldn't be there at all... any internal address there is fishy... why? because the client computers should be configured to send mail via the exchange server and thus they shouldn't connect directly to any other mailserver...

If you made your capture on the exchange server, (maybe because you got to redirect all the internet traffic to it, or maybe because the exchange server is the internet gateway), you must make a display filter in wireshark so you see connections (on port 25, of course) that are not directed to the exchange server...  something like this could work:
!(ip.addr==192.168.0.240) where 192.168.0.240 is the ip address of the exchange server


However, if you suspect the server itself is sending spam, it is really hard by looking at a capture file, unless you search for specific patterns (viagra or penis enlargement maybe? =P)... it may be better off to look into  the server logs unless you have a copy of the reported spam messages...

btw, i just noticed i'm just assuming a rather standard network topology... i might be quite wrong, but i'm kinda lazy to edit the previous post...  it may be a better idea if you tells us how things are connected at your client's office

20120131-EE-VQP-002

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