GraphicsMagick 1.3.26 has a heap overflow in the WriteRGBImage() function in coders/rgb.c when processing multiple frames that have non-identical widths.
https://www.debian.org/security/2018/dsa-4321
https://usn.ubuntu.com/4206-1/
https://lists.debian.org/debian-lts-announce/2018/06/msg00009.html
http://www.securityfocus.com/bid/99978
http://hg.code.sf.net/p/graphicsmagick/code/rev/39961adf974c