Why NFS is listening to a port but not showing the process name, is there any security risk if no firewall is set?

maP1E bluE

10/4/23, 5:45 PM

I'm using ubuntu 22.04 and have mounted an NFS storage, here is my fstab file

ftpback-bhs5-26.ip-149-56-30.net:/export/ftpbackup/ns524316.ip-xxx-xxx-xxx.net /media/backup nfs vers=4.0 0 0

When checking the ports withnetstat -tunlp, I suddenly found two ports that I did not recognize

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:33781           0.0.0.0:*               LISTEN      -
tcp6       0      0 :::35929                :::*                    LISTEN      -

fuser -v 33781/tcp output nothing. I searched for a long time but couldn't find where it came from, and finally I remembered that the only recent changes I had made were to mount NFS storage. I umounted it and the port listening disappeared. Why doesn't it show the process name when it's listening? The output of rpcinfo

root@ubuntu:/home/ubuntu# rpcinfo
   program version netid     address                service    owner
    100000    4    tcp6      ::.0.111               portmapper superuser
    100000    3    tcp6      ::.0.111               portmapper superuser
    100000    4    udp6      ::.0.111               portmapper superuser
    100000    3    udp6      ::.0.111               portmapper superuser
    100000    4    tcp       0.0.0.0.0.111          portmapper superuser
    100000    3    tcp       0.0.0.0.0.111          portmapper superuser
    100000    2    tcp       0.0.0.0.0.111          portmapper superuser
    100000    4    udp       0.0.0.0.0.111          portmapper superuser
    100000    3    udp       0.0.0.0.0.111          portmapper superuser
    100000    2    udp       0.0.0.0.0.111          portmapper superuser
    100000    4    local     /run/rpcbind.sock      portmapper superuser
    100000    3    local     /run/rpcbind.sock      portmapper superuser

Is there a security problem if I don't set up a firewall?

351

0 + 4

storage

nfs

netstat

Simon Richter

10/4/23, 5:56 PM

There is an in-kernel NFS server in Linux that would not be associated with a process in a way that netstat understands.

A.B

10/4/23, 7:23 PM

And to know what these ports are doing, the best bet is `rpcinfo` (it could have a strange format, eg: 33781 might be displayed as .131.245)

maP1E bluE

10/5/23, 6:16 AM

@A.B I added the output of rpcinfo, cannot be associated with the 2 ports above

A.B

10/5/23, 6:28 AM

@maP1EbluE ok. My comment was wrong sorry.

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EN: Why NFS is listening to a port but not showing the process name, is there any security risk if no firewall is set?

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