/usr/share/xscreensaver/config/ is in xscreensaver-gl-extra 5.30-1+deb8u2.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xscreensaver/config/antmaze.xml
/usr/share/xscreensaver/config/atlantis.xml
/usr/share/xscreensaver/config/blocktube.xml
/usr/share/xscreensaver/config/boing.xml
/usr/share/xscreensaver/config/bouncingcow.xml
/usr/share/xscreensaver/config/boxed.xml
/usr/share/xscreensaver/config/cage.xml
/usr/share/xscreensaver/config/carousel.xml
/usr/share/xscreensaver/config/companioncube.xml
/usr/share/xscreensaver/config/crackberg.xml
/usr/share/xscreensaver/config/cube21.xml
/usr/share/xscreensaver/config/cubenetic.xml
/usr/share/xscreensaver/config/cubicgrid.xml
/usr/share/xscreensaver/config/dangerball.xml
/usr/share/xscreensaver/config/extrusion.xml
/usr/share/xscreensaver/config/fliptext.xml
/usr/share/xscreensaver/config/flurry.xml
/usr/share/xscreensaver/config/glhanoi.xml
/usr/share/xscreensaver/config/glplanet.xml
/usr/share/xscreensaver/config/hilbert.xml
/usr/share/xscreensaver/config/hypnowheel.xml
/usr/share/xscreensaver/config/jigsaw.xml
/usr/share/xscreensaver/config/juggler3d.xml
/usr/share/xscreensaver/config/klein.xml
/usr/share/xscreensaver/config/lament.xml
/usr/share/xscreensaver/config/menger.xml
/usr/share/xscreensaver/config/noof.xml
/usr/share/xscreensaver/config/photopile.xml
/usr/share/xscreensaver/config/pinion.xml
/usr/share/xscreensaver/config/providence.xml
/usr/share/xscreensaver/config/rubik.xml
/usr/share/xscreensaver/config/rubikblocks.xml
/usr/share/xscreensaver/config/sballs.xml
/usr/share/xscreensaver/config/skytentacles.xml
/usr/share/xscreensaver/config/sproingies.xml
/usr/share/xscreensaver/config/stairs.xml
/usr/share/xscreensaver/config/starwars.xml
/usr/share/xscreensaver/config/surfaces.xml
/usr/share/xscreensaver/config/tangram.xml
/usr/share/xscreensaver/config/timetunnel.xml
/usr/share/xscreensaver/config/tronbit.xml
/usr/share/xscreensaver/config/unknownpleasures.xml