A heap-based buffer under-read vulnerability exists in libxml2 versions before 2.13.8 and 2.14.x before 2.14.2 in the xmlSchemaIDCFillNodeTables function within xmlschemas.c. Exploitation requires validating a crafted XML document against an XML schema with specific identity constraints or using a crafted XML schema. The vulnerability has a low severity score and does not impact confidentiality or integrity but may affect availability.