ReadCMYKImage in coders/cmyk.c in GraphicsMagick 1.3.26 has a magick/import.c ImportCMYKQuantumType heap-based buffer over-read via a crafted file.
hg.code.sf.net/p/graphicsmagick/code/rev/a9c425688397
lists.debian.org/debian-lts-announce/2018/01/msg00005.html
lists.debian.org/debian-lts-announce/2018/06/msg00009.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PF62B5PJA2JDUOCKJGUQO3SPL74BEYSV/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WHIKB4TP6KBJWT2UIPWL5MWMG5QXKGEJ/
sourceforge.net/p/graphicsmagick/bugs/521/
usn.ubuntu.com/4248-1/
www.debian.org/security/2018/dsa-4321