The ReadJPEGImage function in coders/jpeg.c in GraphicsMagick 1.3.26 creates a pixel cache before a successful read of a scanline, which allows remote attackers to cause a denial of service (resource consumption) via crafted JPEG files.
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/99503
http://hg.code.sf.net/p/graphicsmagick/code/rev/b4139088b49a