The ReadWPGImage function in coders/wpg.c in GraphicsMagick 1.3.26 does not properly validate colormapped images, which allows remote attackers to cause a denial of service (ImportIndexQuantumType invalid write and application crash) or possibly have unspecified other impact via a malformed WPG image.
hg.code.sf.net/p/graphicsmagick/code/rev/e8086faa52d0
lists.debian.org/debian-lts-announce/2018/08/msg00002.html
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PF62B5PJA2JDUOCKJGUQO3SPL74BEYSV/
lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WHIKB4TP6KBJWT2UIPWL5MWMG5QXKGEJ/
sourceforge.net/p/graphicsmagick/bugs/519/
usn.ubuntu.com/4248-1/
www.debian.org/security/2018/dsa-4321