The xml_parse_into_struct function in ext/xml/xml.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 allows remote attackers to cause a denial of service (buffer under-read and segmentation fault) or possibly have unspecified other impact via crafted XML data in the second argument, leading to a parser level of zero.