/usr/share/xscreensaver/config/ is in xscreensaver-gl 5.15-3+deb7u1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/xscreensaver/config/antinspect.xml
/usr/share/xscreensaver/config/antspotlight.xml
/usr/share/xscreensaver/config/atunnel.xml
/usr/share/xscreensaver/config/blinkbox.xml
/usr/share/xscreensaver/config/bubble3d.xml
/usr/share/xscreensaver/config/circuit.xml
/usr/share/xscreensaver/config/cubestorm.xml
/usr/share/xscreensaver/config/endgame.xml
/usr/share/xscreensaver/config/engine.xml
/usr/share/xscreensaver/config/flipflop.xml
/usr/share/xscreensaver/config/flipscreen3d.xml
/usr/share/xscreensaver/config/flyingtoasters.xml
/usr/share/xscreensaver/config/gears.xml
/usr/share/xscreensaver/config/gflux.xml
/usr/share/xscreensaver/config/glblur.xml
/usr/share/xscreensaver/config/glcells.xml
/usr/share/xscreensaver/config/gleidescope.xml
/usr/share/xscreensaver/config/glknots.xml
/usr/share/xscreensaver/config/glmatrix.xml
/usr/share/xscreensaver/config/glschool.xml
/usr/share/xscreensaver/config/glslideshow.xml
/usr/share/xscreensaver/config/glsnake.xml
/usr/share/xscreensaver/config/gltext.xml
/usr/share/xscreensaver/config/hypertorus.xml
/usr/share/xscreensaver/config/jigglypuff.xml
/usr/share/xscreensaver/config/lavalite.xml
/usr/share/xscreensaver/config/lockward.xml
/usr/share/xscreensaver/config/mirrorblob.xml
/usr/share/xscreensaver/config/moebius.xml
/usr/share/xscreensaver/config/moebiusgears.xml
/usr/share/xscreensaver/config/molecule.xml
/usr/share/xscreensaver/config/morph3d.xml
/usr/share/xscreensaver/config/pipes.xml
/usr/share/xscreensaver/config/polyhedra.xml
/usr/share/xscreensaver/config/polytopes.xml
/usr/share/xscreensaver/config/pulsar.xml
/usr/share/xscreensaver/config/queens.xml
/usr/share/xscreensaver/config/sierpinski3d.xml
/usr/share/xscreensaver/config/sonar.xml
/usr/share/xscreensaver/config/spheremonics.xml
/usr/share/xscreensaver/config/stonerview.xml
/usr/share/xscreensaver/config/superquadrics.xml
/usr/share/xscreensaver/config/topblock.xml
/usr/share/xscreensaver/config/voronoi.xml