In Dovecot before 2.2.36.3 and 2.3.x before 2.3.5.1, a local attacker can cause a buffer overflow in the indexer-worker process, which can be used to elevate to root. This occurs because of missing checks in the fts and pop3-uidl components.
https://www.debian.org/security/2019/dsa-4418
https://usn.ubuntu.com/3928-1/
https://security.gentoo.org/glsa/201904-19
https://seclists.org/bugtraq/2019/Mar/59
https://lists.debian.org/debian-lts-announce/2019/03/msg00038.html
https://dovecot.org/security.html
https://dovecot.org/list/dovecot-news/2019-March/000403.html
http://www.securityfocus.com/bid/107672
http://www.openwall.com/lists/oss-security/2019/03/28/1
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00067.html
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00060.html