ReadPNMImage in coders/pnm.c in GraphicsMagick 1.3.26 does not ensure the correct number of colors for the XV 332 format, leading to a NULL Pointer Dereference.
https://www.debian.org/security/2018/dsa-4321
https://usn.ubuntu.com/4232-1/
https://sourceforge.net/p/graphicsmagick/bugs/466/
https://sourceforge.net/p/graphicsmagick/bugs/465/
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html
http://www.securityfocus.com/bid/100877
http://hg.graphicsmagick.org/hg/GraphicsMagick?cmd=changeset%3Bnode=fb09ca6dd22c