GnuTLS -- double free, invalid pointer access

The GnuTLS project reports:

Tavis Ormandy from Google Project Zero found a memory
corruption (double free) vulnerability in the certificate
verification API. Any client or server application that verifies
X.509 certificates with GnuTLS 3.5.8 or later is affected.
It was found using the TLS fuzzer tools that decoding a
malformed TLS1.3 asynchronous message can cause a server crash
via an invalid pointer access. The issue affects GnuTLS server
applications since 3.6.4.