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Possibility of a whitelisted (Internet) IP address being spoofed

Posted on 2016-07-29
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Last Modified: 2016-08-01
Currently we don't permit Tcp25 from public Internet to our Exchange server:
all emails go to our internet-facing ProofPoint , then only ProofPoint forward
it our Exchange 2010 server

We plan to permit Tcp 25 direct into our local Exchange 2010 server from an
IP address ie whitelist this public IP address which is our HQ's ProofPoint IP:

a) if it's only a firewall rule that permit our HQ's ProofPoint IP to come in to
    our Exchange server, I guess this IP can be spoofed.  What if this IP is also
    whitelisted, can it be spoofed as well?  I read only Udp can be spoofed or
    is this mistaken?

b) is there any risk of MITM attack for this forwarding ?  The forwarded emails
     are not encrypted
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Question by:sunhux
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by:
Mal Osborne earned 1000 total points
ID: 41734298
A) Probably not. A device spoofing your IP address would somehow need to be able to the routed from and too.

B) In theory, anyone who can get to see your traffic could implement a "Man in the middle" attack, unless encryption is used. Unencrypted email is not very secure.
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by:John Hurst
John Hurst earned 1000 total points
ID: 41734560
We plan to permit TCP 25 direct

At a client, my own consulting machine has a DHCP reservation and then that IP address is allowed in the Juniper firewall so that I may send out email separately from their email system.

I do not think you are at excessive risk for doing this. My machine does not compromise the client network.
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Author Comment

by:sunhux
ID: 41734739
https://community.mimecast.com/docs/DOC-1419

Refer to above link: there are indications in the link that allude to IP addr spoofing:

Create an Anti-Spoofing Policy to Allow "Spoofing Based on IP"

5.Enter the list of hostnames to apply the bypass to in the Hostnames box. Confirmation is issued
   that the "IP address used by the sending server matches the hostname specified"
   ie for the protection to be effective, it needs both IP address plus hostname to match
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by:John Hurst
John Hurst earned 1000 total points
ID: 41735147
I looked quickly and will look again when I have time. If your firewall is otherwise properly locked down, open a port for one IP address only (not everyone) is not likely to cause harm.
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