An issue was discovered in GnuTLS before 3.6.15. A server can trigger a NULL pointer dereference in a TLS 1.3 client if a no_renegotiation alert is sent with unexpected timing, and then an invalid second handshake occurs. The crash happens in the application's error handling path, where the gnutls_deinit function is called after detecting a handshake failure.
https://www.gnutls.org/security-new.html#GNUTLS-SA-2020-09-04
https://usn.ubuntu.com/4491-1/
https://security.netapp.com/advisory/ntap-20200911-0006/
https://security.gentoo.org/glsa/202009-01
https://gitlab.com/gnutls/gnutls/-/issues/1071
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00060.html
http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00054.html