GraphicsMagick 1.3.26 has a segmentation violation in the WriteMAPImage() function in coders/map.c when processing a non-colormapped image, a different vulnerability than CVE-2017-11642.
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://hg.code.sf.net/p/graphicsmagick/code/rev/29550606d8b9