The vulnerability stems from improper XML parsing configurations in GanttProjectReader and PhoenixReader components. The commit diff shows the fix involved adding XMLReaderHelper with 'disallow-doctype-decl' feature to prevent XXE. Prior to this fix, these readers used standard JAXB unmarshalling without secure XML parser settings, making them vulnerable to XXE via malicious XML entities. The advisory explicitly names these components as affected, and the patch directly addresses their XML handling.