GraphicsMagick 1.3.26 has a denial of service issue in ReadJNXImage() in coders/jnx.c whereby large amounts of CPU and memory resources may be consumed although the file itself does not support the requests.
http://openwall.com/lists/oss-security/2017/08/31/3
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html