3CX PhoneSystem 01 SIP Server uses all available memory

[sip.bg]

What could be the reason 3CX PhoneSystem01 SIP Server service to use all available memory in few days from restart of services ?
The 3CX server is running on Debian 9, latest SP3.

 

[Sopock]

@nickybrg
As a result we can learn from this case how unsupported, old or legacy phones can be turned into Authenticated and Admin Approved, Denial of service Demon Bots with one .,. actually 2 scopes in life - 1) Make a call from A to B and 2) FLOOD / DOS the server with unnecessary subscribes and sip messages causing the server to eat up all the operating system's memory resources ..