Questions related to lsof command output

multisites
multisites used Ask the Experts™
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Hi,
I have a Linux Centos / Apache Webserver. It has just Domains, no mailboxes. But it runs Postfix because of the Domains' forms.
Frequently, when I issue a "lsof -i" command, it outputs things like in the attached text file. My questions:
1) What does this output really mean? Is this Server being used for relay? It has not open relay.
2) If so, is there anything I could imediately do to stop it?

Thanks.

Mario./
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Author

Commented:
I forgot to attach the file. Here it goes.
lsof.txt
nociSoftware Engineer
Distinguished Expert 2018

Commented:
Lets disect the first line:

smtp    13229  postfix   12u  IPv4 11809871       TCP srv2.multisitesdominios.com.br:49922->mx01.admincontrolpanel.com:smtp (ESTABLISHED)

it means youy have sessions that run from a process named smtp, processid 13229, owner postfix,
12u is the file handle 12, opened for update (others are r=read, w=write).
The file type on the handles is an IPv4 socket, the number is not realy important here.
The IPv4 Socket is TCP session, started on
srv2.multisitesdominios.com.br   port 49922 with destination: mx01.admincontrolpanel.com SMTP (port 25), the lik state is established (= active).

SYN_SENT is a starting connection,


You need to check postfix logging if this is legitemite mail. by verifying e-mail addresses (source & destination).
If you have mail sending forms, it might be that they are abused by robot posts.
you might have a code injection active (that would mean you also have a process running a php script sending mails...)

You need to determine from the postfix logging to what extent this is harmfull or not.
nociSoftware Engineer
Distinguished Expert 2018

Commented:
To stop it quickly, stop postfix...
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Author

Commented:
Hi, noci:

You said some important things. As a matter of fact I also believe we may have any form(s) being abused. My question: is there a way to find out what are them, or from which of our hosted Domains it this happening?

My concern in stopping Postfix is that I need Postfix so that normal forms data from our Domains can be sent.

Anyway, thanks for your comments.

Author

Commented:
The only possibility I see is really form abuse, because, as I said, this Server has not mailboxes, just Domains.
Software Engineer
Distinguished Expert 2018
Commented:
If the sender through a form is fixed, you should be able to find out which form is used.
(Postfix logging)
If the receiver is fixed. you can trace the mail (through postfix logging).
( this might be different for different forms).

You might be able to include a header line through a form that identifies the site involved?
to stop abuse, try to use things like Captcha's.

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