In FreeBSD 12.1-STABLE before r364644, 11.4-STABLE before r364651, 12.1-RELEASE before p9, 11.4-RELEASE before p3, and 11.3-RELEASE before p13, improper handling in the kernel causes a use-after-free bug by sending large user messages from multiple threads on the same SCTP socket. The use-after-free situation may result in unintended kernel behaviour including a kernel panic.
https://support.apple.com/kb/HT212325
https://support.apple.com/kb/HT212324
https://support.apple.com/kb/HT212323
https://support.apple.com/kb/HT212321
https://support.apple.com/kb/HT212319
https://support.apple.com/kb/HT212318
https://support.apple.com/kb/HT212317
https://security.FreeBSD.org/advisories/FreeBSD-SA-20:25.sctp.asc
http://seclists.org/fulldisclosure/2021/Apr/59
http://seclists.org/fulldisclosure/2021/Apr/58
http://seclists.org/fulldisclosure/2021/Apr/57