In Artifex Ghostscript before 9.26, a carefully crafted PDF file can trigger an extremely long running computation when parsing the file.
https://www.ghostscript.com/doc/9.26/History9.htm
https://lists.debian.org/debian-lts-announce/2018/12/msg00019.html
https://bugzilla.redhat.com/show_bug.cgi?id=1655607
https://bugs.ghostscript.com/show_bug.cgi?id=699856