/usr/share/live/images/gnome-desktop/config/bootloaders/syslinux/vesamenu.c32 is in live-image-gnome-desktop 4.0~a5-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/live/images/gnome-desktop/config/bootloaders/syslinux/../../../../../../../lib/syslinux/vesamenu.c32