ext/imap/php_imap.c in PHP 5.x and 7.x before 7.3.0 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via an empty string in the message argument to the imap_mail function.
https://www.debian.org/security/2018/dsa-4353
https://security.netapp.com/advisory/ntap-20181221-0003/
https://lists.debian.org/debian-lts-announce/2018/12/msg00006.html
https://bugs.php.net/bug.php?id=77020
http://www.securityfocus.com/bid/106143
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00044.html
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00041.html