ReadOneJNGImage in coders/png.c in GraphicsMagick version 1.3.26 does not properly validate JNG data, leading to a denial of service (assertion failure in magick/pixel_cache.c, and application crash).
https://usn.ubuntu.com/4232-1/
https://sourceforge.net/p/graphicsmagick/bugs/439/
https://blogs.gentoo.org/ago/2017/09/19/graphicsmagick-assertion-failure-in-pixel_cache-c/
http://www.securityfocus.com/bid/100958
http://hg.code.sf.net/p/graphicsmagick/code/rev/358608a46f0a