The ReadJNGImage and ReadOneJNGImage functions in coders/png.c in GraphicsMagick 1.3.26 do not properly manage image pointers after certain error conditions, which allows remote attackers to conduct use-after-free attacks via a crafted file, related to a ReadMNGImage out-of-order CloseBlob call. NOTE: this vulnerability exists because of an incomplete fix for CVE-2017-11403.