An issue has been found in Mini-XML (aka mxml) 2.12. It is a use-after-free in mxmlWalkNext in mxml-search.c, as demonstrated by mxmldoc.
https://github.com/michaelrsweet/mxml/issues/234
https://github.com/fouzhe/security/tree/master/mxml#heap-use-after-free-in-function-mxmlwalknext