In Dovecot before 2.3.11.3, sending a specially formatted RPA request will crash the auth service because a length of zero is mishandled.
https://www.openwall.com/lists/oss-security/2020/08/12/3
https://www.debian.org/security/2020/dsa-4745
https://usn.ubuntu.com/4456-2/
https://usn.ubuntu.com/4456-1/
https://security.gentoo.org/glsa/202009-02
https://lists.debian.org/debian-lts-announce/2020/08/msg00024.html
http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00059.html
http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00048.html