/usr/include/CGAL/internal/ is in libcgal-dev 4.2-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/CGAL/internal/AABB_tree/
/usr/include/CGAL/internal/AABB_tree/AABB_drawing_traits.h
/usr/include/CGAL/internal/AABB_tree/AABB_node.h
/usr/include/CGAL/internal/AABB_tree/AABB_search_tree.h
/usr/include/CGAL/internal/AABB_tree/AABB_traversal_traits.h
/usr/include/CGAL/internal/AABB_tree/nearest_point_segment_3.h
/usr/include/CGAL/internal/AABB_tree/nearest_point_triangle_3.h
/usr/include/CGAL/internal/Classification_type.h
/usr/include/CGAL/internal/Combinatorial_map_group_functors.h
/usr/include/CGAL/internal/Combinatorial_map_internal_functors.h
/usr/include/CGAL/internal/Combinatorial_map_sewable.h
/usr/include/CGAL/internal/Combinatorial_map_utility.h
/usr/include/CGAL/internal/Combinatorial_map_utility_novariadic.h
/usr/include/CGAL/internal/Delaunay_triangulation_hierarchy_3.h
/usr/include/CGAL/internal/Dummy_tds_3.h
/usr/include/CGAL/internal/Exact_type_selector.h
/usr/include/CGAL/internal/Intersections_3/
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Bbox_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Line_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Plane_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Ray_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Segment_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Sphere_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Bbox_3_Triangle_3_do_intersect.h
/usr/include/CGAL/internal/Intersections_3/Triangle_3_Line_3_intersection.h
/usr/include/CGAL/internal/Intersections_3/Triangle_3_Ray_3_intersection.h
/usr/include/CGAL/internal/Intersections_3/Triangle_3_Segment_3_intersection.h
/usr/include/CGAL/internal/K_neighbor_search.h
/usr/include/CGAL/internal/Lazy_alpha_nt_2.h
/usr/include/CGAL/internal/Lazy_alpha_nt_3.h
/usr/include/CGAL/internal/Projection_traits_3.h
/usr/include/CGAL/internal/Regular_triangulation_filtered_traits_3.h
/usr/include/CGAL/internal/Static_filters/
/usr/include/CGAL/internal/Static_filters/Angle_3.h
/usr/include/CGAL/internal/Static_filters/Compare_squared_radius_3.h
/usr/include/CGAL/internal/Static_filters/Compare_weighted_squared_radius_3.h
/usr/include/CGAL/internal/Static_filters/Compare_y_at_x_2.h
/usr/include/CGAL/internal/Static_filters/Coplanar_orientation_3.h
/usr/include/CGAL/internal/Static_filters/Coplanar_side_of_bounded_circle_3.h
/usr/include/CGAL/internal/Static_filters/Do_intersect_3.h
/usr/include/CGAL/internal/Static_filters/Equal_3.h
/usr/include/CGAL/internal/Static_filters/Is_degenerate_3.h
/usr/include/CGAL/internal/Static_filters/Orientation_2.h
/usr/include/CGAL/internal/Static_filters/Orientation_3.h
/usr/include/CGAL/internal/Static_filters/Periodic_3_orientation_3.h
/usr/include/CGAL/internal/Static_filters/Periodic_3_side_of_oriented_sphere_3.h
/usr/include/CGAL/internal/Static_filters/Power_test_3.h
/usr/include/CGAL/internal/Static_filters/Regular_triangulation_static_filters_traits_3.h
/usr/include/CGAL/internal/Static_filters/Side_of_oriented_circle_2.h
/usr/include/CGAL/internal/Static_filters/Side_of_oriented_sphere_3.h
/usr/include/CGAL/internal/Static_filters/Static_filter_error.h
/usr/include/CGAL/internal/Static_filters/Static_filters.h
/usr/include/CGAL/internal/Static_filters/tools.h
/usr/include/CGAL/internal/Triangulation_ds_circulators_3.h
/usr/include/CGAL/internal/Triangulation_ds_iterators_3.h
/usr/include/CGAL/internal/boost/
/usr/include/CGAL/internal/boost/array_binary_tree.hpp
/usr/include/CGAL/internal/boost/mutable_heap.hpp
/usr/include/CGAL/internal/boost/mutable_queue.hpp
/usr/include/CGAL/internal/boost/property_map.h
/usr/include/CGAL/internal/bounded_priority_queue.h
/usr/include/CGAL/internal/container_fwd_fixed.hpp
/usr/include/CGAL/internal/corefinement/
/usr/include/CGAL/internal/corefinement/Combinatorial_map_for_corefinement.h
/usr/include/CGAL/internal/corefinement/Polyhedron_constness_types.h
/usr/include/CGAL/internal/corefinement/Polyhedron_subset_extraction.h
/usr/include/CGAL/internal/corefinement/intersection_coplanar_triangles_3.h
/usr/include/CGAL/internal/corefinement/intersection_triangle_segment_3.h
/usr/include/CGAL/internal/corefinement/intersection_triangle_segment_3_coplanar.h
/usr/include/CGAL/internal/deprecation_warning.h
/usr/include/CGAL/internal/info_check.h