Improper Restriction of XML External Entity Reference
Concrete CMS (formerly concrete5) versions prior to 8.5.10, and 9.0.x prior to 9.1.3 is vulnerable to XXE based DNS requests leading to IP disclosure.
CWE-611 - Improper Restriction of XML External Entity Reference
Listed 4th in the 'OWASP Top Ten', XML External Entities (XXE) vulnerability allows attackers to provide an XML input that contains an external entity. When the XML is parsed, it can cause data extraction and manipulation, execution of commands, denial-of-service attacks, and server-side request forgery.