The ReadOneJNGImage and ReadJNGImage functions in coders/png.c in GraphicsMagick 1.3.26 allow remote attackers to cause a denial of service (magick/blob.c CloseBlob use-after-free) or possibly have unspecified other impact via a crafted file, a related issue to CVE-2017-11403.
https://lists.debian.org/debian-lts-announce/2018/03/msg00025.html
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html