A NULL pointer dereference vulnerability exists in eXcall_api.c in Antisip eXosip2 through 5.2.0 when handling certain 3xx redirect responses.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2021-19449
http://git.savannah.nongnu.org/cgit/exosip.git/commit/?id=f2ed389fe84613512cc560127883e51e6cf8c054