Apache CloudStack version 4.5.0 and later has a SAML 2.0 authentication Service Provider plugin which is found to be vulnerable to XML external entity (XXE) injection. This plugin is not enabled by default and the attacker would require that this plugin be enabled to exploit the vulnerability. When the SAML 2.0 plugin is enabled in affected versions of Apache CloudStack could potentially allow the exploitation of XXE vulnerabilities. The SAML 2.0 messages constructed during the authentication flow in Apache CloudStack are XML-based and the XML data is parsed by various standard libraries that are now understood to be vulnerable to XXE injection attacks such as arbitrary file reading, possible denial of service, server-side request forgery (SSRF) on the CloudStack management server.