Asterisk Project Security Advisory – The chan_pjsip channel driver uses a queue approach for actions relating to SIP sessions. There exists a race condition where actions may be queued to answer a session or send ringing AFTER a SIP session has been terminated using a CANCEL request. The code will incorrectly assume that the SIP session is still active and attempt to send the SIP response. The PJSIP library does not expect the SIP session to be in the disconnected state when sending the response and asserts.