I have the following setup:
SIP are configured between CUCM-CUBE and CUBE--ITSP SIP server, both CUCM and CUBE are behind corp firewall using private IP addresses, on firewall we have a static mapping to CUBE and we only allow SIP traffic and audio UDP traffic come in, outbound long distance calls are routed on CUCM to CUBE and then to ITSP, everything worked fine until today our ITSP shut us down because excessive International calls, we were obviously being hacked. Since syslog does not log SIP level information, I am in the dark on how to proceed to troubleshoot.
I am wondering how can anybody hack into our SIP lines and make international calls? the ITSP only accepts our source IP for SIP signaling, if somebody spoof our legitimate IP then how can they get return traffic from ITSP? any pointers will be greately appreciated.