Question about application and port being run

liddithespy · 10-05-2021, 04:51 PM

Hi, not sure what this application is being used for
the app is named MASTER
the port is 25

I have just in installed popOS
any thoughts on the best way to find the purpose of this app and if its safE?

computersavvy · 10-05-2021, 05:03 PM

PopOS?
No such app?
commonly used port?
Very suspicious post.

michaelk · 10-05-2021, 05:10 PM

FYI... Pop OS is a linux distribution and master is the process that runs the postfix server which uses port 25.

liddithespy · 10-05-2021, 05:14 PM

ya, master looked funny.. never seen that app. I caught it after using UFW and saw it on port 25. Should I wipe OS ?

michaelk · 10-05-2021, 05:43 PM

I am not sure how PoP is configured but usually postfix only listens to localhost (internal only) by default. Some programs use postfix to send messages like cron so it is nothing to worry about.

As a check you can install nmap if not already and test port 25

Code:

nmap localhost -p 25

Starting Nmap 6.40 ( http://nmap.org ) at 2021-10-05 ...
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000065s latency).
Other addresses for localhost (not scanned): 127.0.0.1
PORT   STATE SERVICE
25/tcp open  smtp

nmap IP_address -p 25

Starting Nmap 6.40 ( http://nmap.org ) at 2021-10-05...
Nmap scan report for server (IP_address)
Host is up (0.000060s latency).
rDNS record for 192.168.0.2: server
PORT   STATE  SERVICE
25/tcp closed smtp

Where IP_address is the private IP address of your computer. Look at the output of the command ip a. Your actual output might be different but the line that starts with inet is your LAN address.

Code:

2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether bc:30:5b:b9:d1:5a brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.2/24 brd 192.168.0.255 scope global noprefixroute dynamic enp0s25

boughtonp · 10-05-2021, 05:45 PM

Searching for what is master on port 25 doesn't give a direct answer, but does make it clear this is Postfix related.

So, searching then for "postfix master" reveals the answer http://www.postfix.org/master.8.html

Quote:

The master(8) daemon is the resident process that runs Postfix daemons
on demand: daemons to send or receive messages via the network, daemons
to deliver mail locally, etc. These daemons are created on demand up
to a configurable maximum number per service.

computersavvy · 10-06-2021, 02:44 PM

I have never used PopOS nor seen a service daemon called MASTER so I would have been concerned as well. It obviously was using the smtp port, but the name concerned me.

Thanks for the information.