Someone is trying to make calls without being registered

I have this showing up periodically in my logs (never the same IP)

[Jan 31 10:43:04] NOTICE[10347][C-0000002e]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10120) to extension '00972592573636' rejected because extension not found in context 'unauthenticated'. == Using SIP RTP CoS mark 5 [Jan 31 10:43:04] NOTICE[10347][C-0000002f]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10827) to extension '011972592573636' rejected because extension not found in context 'unauthenticated'. == Using SIP RTP CoS mark 5 [Jan 31 10:43:05] NOTICE[10347][C-00000030]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10123) to extension '810972592573636' rejected because extension not found in context 'unauthenticated'. == Using SIP RTP CoS mark 5 [Jan 31 10:43:05] NOTICE[10347][C-00000031]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10123) to extension '0011972592573636' rejected because extension not found in context 'unauthenticated'. == Using SIP RTP CoS mark 5 [Jan 31 10:43:05] NOTICE[10347][C-00000032]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10121) to extension '900972592573636' rejected because extension not found in context 'unauthenticated'. == Using SIP RTP CoS mark 5 [Jan 31 10:43:06] NOTICE[10347][C-00000033]: chan_sip.c:25108 handle_request_invite: Call from '' (176.58.73.167:10121) to extension '800972592573636' rejected because extension not found in context 'unauthenticated'.

I guess this is someone poking my PBX trying to see if they can place calls to what seems to be a mobile number in Israel.

Did I misconfigure something for this to happen or is it normal behaviour?

Yes you don’t secure your Box.

Close external ports if you don’t need it.
Set allowguest=no
Use a blocking tool like fail2ban or blockhost.

Read the best practice TXT in the asterisk source directory.