The ReadOneJNGImage function in coders/png.c in GraphicsMagick 1.3.26 allows remote attackers to cause a denial of service (application crash) during JNG reading via a zero-length color_image data structure.
https://www.debian.org/security/2018/dsa-4321
https://usn.ubuntu.com/4206-1/
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html
http://www.securityfocus.com/bid/99498
http://hg.code.sf.net/p/graphicsmagick/code/rev/dea93a690fc1
http://hg.code.sf.net/p/graphicsmagick/code/rev/d445af60a8d5