In FreeBSD 12.1-STABLE before r352509, 11.3-STABLE before r352509, and 11.3-RELEASE before p9, an unprivileged local user can trigger a use-after-free situation due to improper checking in SCTP when an application tries to update an SCTP-AUTH shared key.
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.