Improper Restriction of XML External Entity Reference
PMD before 6.0.0 processes XML external entities in ruleset files it parses as part of the analysis process, allowing attackers tampering it (either by direct modification or MITM attacks when using remote rulesets) to perform information disclosure, denial of service, or request forgery attacks. (PMD 6.x is unaffected because of a 2017-09-15 change.)
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.