The build_filter_chain function in pdf/pdf-stream.c in Artifex MuPDF before 2017-09-25 mishandles a certain case where a variable may reside in a register, which allows remote attackers to cause a denial of service (Fitz fz_drop_imp use-after-free and application crash) or possibly have unspecified other impact via a crafted PDF document.
https://bugs.ghostscript.com/show_bug.cgi?id=698592
http://git.ghostscript.com/?p=mupdf.git%3Bh=c2663e51238ec8256da7fc61ad580db891d9fe9a