A flaw was found in htmldoc in v1.9.12 and before. Null pointer dereference in file_extension(),in file.c may lead to execute arbitrary code and denial of service.
https://bugzilla.redhat.com/show_bug.cgi?id=1967041
https://github.com/michaelrsweet/htmldoc/commit/19c582fb32eac74b57e155cffbb529377a9e751a