In GraphicsMagick 1.3.28, there is a divide-by-zero in the ReadMNGImage function of coders/png.c. Remote attackers could leverage this vulnerability to cause a crash and denial of service via a crafted mng file.
https://www.debian.org/security/2018/dsa-4321
https://sourceforge.net/p/graphicsmagick/bugs/554/
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html
https://lists.debian.org/debian-lts-announce/2018/03/msg00025.html