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.
https://www.debian.org/security/2018/dsa-4321
https://usn.ubuntu.com/4222-1/
https://lists.debian.org/debian-lts-announce/2018/08/msg00002.html
http://www.securityfocus.com/bid/100570
http://openwall.com/lists/oss-security/2017/08/31/3
http://hg.code.sf.net/p/graphicsmagick/code/rev/b037d79b6ccd