A NULL pointer dereference vulnerability exists in the xpath.c:xmlXPathCompOpEval()
function of libxml2 through 2.9.8 when parsing an invalid XPath expression in the XPATH_OP_AND
or XPATH_OP_OR
case. Applications processing untrusted XSL format inputs with the use of the libxml2 library may be vulnerable to a denial of service attack due to a crash of the application.