CVE-2020-28327

A res_pjsip_session crash was discovered in Asterisk Open Source 13.x
before 13.37.1, 16.x before 16.14.1, 17.x before 17.8.1, and 18.x before
18.0.1. and Certified Asterisk before 16.8-cert5. Upon receiving a new SIP
Invite, Asterisk did not return the created dialog locked or referenced.
This caused a gap between the creation of the dialog object, and its next
use by the thread that created it. Depending on some off-nominal
circumstances and timing, it was possible for another thread to free said
dialog in this gap. Asterisk could then crash when the dialog object, or
any of its dependent objects, were dereferenced or accessed next by the
initial-creation thread. Note, however, that this crash can only occur when
using a connection-oriented protocol (e.g., TCP or TLS, but not UDP) for
SIP transport. Also, the remote client must be authenticated, or Asterisk
must be configured for anonymous calling.