In ReadOneJNGImage in coders/png.c in GraphicsMagick 1.3.26, a Null Pointer Dereference occurs while transferring JPEG scanlines, related to a PixelPacket pointer.
Ubuntu Security Notice 4232-1 - It was discovered that GraphicsMagick incorrectly handled certain image files. An attacker could possibly use this issue to cause a denial of service or other unspecified impact.