Hello everyone!
How are you? Hope you are doing fine.
Im experiencing this message on the TAB ConfigServer Security & Firewall - csf v14.02.
Here you can see where is located this message: Screenshot by Lightshot
Awaiting some light over this issue in order to feel a liiiitle bit less paranoid with a clean firewall! 
My instance is under ubuntu 18.04 LTS.
Love!
r.
Ps: I just run sudo apt-get install perl
But this appears:
Reading package lists… Done
Building dependency tree
Reading state information… Done
perl is already the newest version (5.26.1-6ubuntu0.3).
perl set to manually installed.
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
Any suggestion?
Thanks a LOT!
Not warning anymore. 
Have a beautiful rest of the week, be safe and thanks once again. 