In ImageMagick 7.0.7-1 Q16, the PersistPixelCache function in magick/cache.c mishandles the pixel cache nexus, which allows remote attackers to cause a denial of service (NULL pointer dereference in the function GetVirtualPixels in MagickCore/cache.c) via a crafted file.
https://usn.ubuntu.com/3681-1/
https://lists.debian.org/debian-lts-announce/2020/09/msg00007.html
https://lists.debian.org/debian-lts-announce/2019/05/msg00015.html