I have tcpdump saving all SIP traffic to files. Based on the Call-ID: 3a5e35a4-41f6-1235-7db0-000c29e59fdd we can see at frame 5, I identified the INVITE that crashed kamailio as this one:
INVITE sip:RelayToGateway@202.173.5.181:5060 SIP/2.0 Via: SIP/2.0/UDP 202.173.5.217;rport;branch=z9hG4bK7828rtcXNgZKK Max-Forwards: 15 From: "05068694099" sip:05068694099@softphone.spc.brastel.ne.jp;tag=60tpj2K802F1r To: sip:6285747462406@202.173.5.181:5060 Call-ID: 3a5e35a4-41f6-1235-7db0-000c29e59fdd CSeq: 100817517 INVITE Contact: sip:mod_sofia@202.173.5.217:5060 User-Agent: FLIP transcoder Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, NOTIFY Supported: timer, path, replaces Allow-Events: talk, hold, conference, refer Content-Type: application/sdp Content-Disposition: session Content-Length: 293 X-FlipData: ruri=sip:6285747462406@softphone.spc.brastel.ne.jp;carrier=8;pai_uri=sip:05068694099@softphone.spc.brastel.ne.jp
v=0 o=FreeSWITCH 1482259707 1482259708 IN IP4 202.173.5.217 s=FreeSWITCH c=IN IP4 202.173.5.217 t=0 0 m=audio 47456 RTP/AVP 0 8 3 101 13 a=rtpmap:0 PCMU/8000 a=rtpmap:8 PCMA/8000 a=rtpmap:3 GSM/8000 a=rtpmap:101 telephone-event/8000 a=fmtp:101 0-16 a=rtpmap:13 CN/8000 a=ptime:20
This is a request from FreeSWITCH acting as a transcoder and I don't see anything out of ordinary in it.