/usr/include/CGAL/Circular_kernel_2/ is in libcgal-dev 4.2-5ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/CGAL/Circular_kernel_2/Circular_arc_2.h
/usr/include/CGAL/Circular_kernel_2/Circular_arc_point_2.h
/usr/include/CGAL/Circular_kernel_2/Line_arc_2.h
/usr/include/CGAL/Circular_kernel_2/function_objects_on_circle_2.h
/usr/include/CGAL/Circular_kernel_2/function_objects_on_line_2.h
/usr/include/CGAL/Circular_kernel_2/function_objects_polynomial_circular.h
/usr/include/CGAL/Circular_kernel_2/interface_macros.h
/usr/include/CGAL/Circular_kernel_2/internal_functions_on_circle_2.h
/usr/include/CGAL/Circular_kernel_2/internal_functions_on_circular_arc_2.h
/usr/include/CGAL/Circular_kernel_2/internal_functions_on_line_2.h
/usr/include/CGAL/Circular_kernel_2/internal_functions_on_line_arc_2.h
/usr/include/CGAL/Circular_kernel_2/intersection_line_2_circle_2_map.h