libs/zbxmedia/eztexting.c in Zabbix 1.8.x before 1.8.18rc1, 2.0.x before 2.0.8rc1, and 2.1.x before 2.1.2 does not properly set the CURLOPT_SSL_VERIFYHOST option for libcurl, which allows man-in-the-middle attackers to spoof SSL servers via an arbitrary valid certificate.
https://support.zabbix.com/browse/ZBX-5924