/usr/include/cereal/external/ is in libcereal-dev 1.1.2-4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/cereal/external/base64.hpp
/usr/include/cereal/external/rapidjson/
/usr/include/cereal/external/rapidjson/document.h
/usr/include/cereal/external/rapidjson/filestream.h
/usr/include/cereal/external/rapidjson/genericstream.h
/usr/include/cereal/external/rapidjson/internal/
/usr/include/cereal/external/rapidjson/internal/pow10.h
/usr/include/cereal/external/rapidjson/internal/stack.h
/usr/include/cereal/external/rapidjson/internal/strfunc.h
/usr/include/cereal/external/rapidjson/prettywriter.h
/usr/include/cereal/external/rapidjson/rapidjson.h
/usr/include/cereal/external/rapidjson/reader.h
/usr/include/cereal/external/rapidjson/stringbuffer.h
/usr/include/cereal/external/rapidjson/writer.h
/usr/include/cereal/external/rapidxml/
/usr/include/cereal/external/rapidxml/manual.html
/usr/include/cereal/external/rapidxml/rapidxml.hpp
/usr/include/cereal/external/rapidxml/rapidxml_iterators.hpp
/usr/include/cereal/external/rapidxml/rapidxml_print.hpp
/usr/include/cereal/external/rapidxml/rapidxml_utils.hpp