Details for this vulnerability have not been published by NIST at this point. Descriptions from software vendor advisories for this issue are provided below.
The Asterisk project reports:
When T.38 faxing is done in Asterisk a T.38 reinvite
may be sent to an endpoint to switch it to T.38. If the
endpoint responds with an improperly formatted SDP answer
including both a T.38 UDPTL stream and an audio or video
stream containing only codecs not allowed on the SIP peer
or user a crash will occur. The code incorrectly assumes
that there will be at least one common codec when T.38
is also in the SDP answer.