The DrawImage function in magick/render.c in GraphicsMagick 1.3.26 does not properly look for pop keywords that are associated with push keywords, which allows remote attackers to cause a denial of service (negative strncpy and application crash) or possibly have unspecified other impact via a crafted file.
https://lists.debian.org/debian-lts-announce/2017/11/msg00016.html
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html
https://sourceforge.net/p/graphicsmagick/bugs/517/