ReadGRAYImage in coders/gray.c in GraphicsMagick 1.3.26 has a magick/import.c ImportGrayQuantumType heap-based buffer over-read via a crafted file.
https://lists.debian.org/debian-lts-announce/2018/01/msg00005.html
https://lists.debian.org/debian-lts-announce/2018/06/msg00009.html
https://sourceforge.net/p/graphicsmagick/bugs/522/