XML external entity (XXE) vulnerability in Zabbix 1.8.x before 1.8.21rc1, 2.0.x before 2.0.13rc1, 2.2.x before 2.2.5rc1, and 2.3.x before 2.3.2 allows remote attackers to read arbitrary files or potentially execute arbitrary code via a crafted DTD in an XML request.