If you want to allow paths spanning multiple folders, a common strategy is to make sure that the constructed
file path is contained within a safe root folder. First, normalize the path using os.path.normpath or
-os.path.realpath to remove any ".." segments. Then check that the normalized path starts with the
+os.path.realpath (make sure to use the latter if symlinks are a consideration)
+to remove any internal ".." segments and/or follow links. Then check that the normalized path starts with the
root folder. Note that the normalization step is important, since otherwise even a path that starts with the root
folder could be used to access files outside the root folder.
More restrictive options include using a library function like werkzeug.utils.secure_filename to eliminate
-any special characters from the file path, or restricting the path to an allow list of safe paths. These options are
+any special characters from the file path, or restricting the path to a known list of safe paths. These options are
safe, but can only be used in particular circumstances.