The python scripts in this page and in the next one will try to save an uploaded file in a directory named files in the directory where it is running. If the directory where the script is running is /path/to/dir then the /path/to/dir/files directory must exist otherwise it will fail.
To upload a file the HTML form must have the enctype attribute set to multipart/form-data. The input tag with the file type will create a "Browse" button.
The getfirst() and getlist() methods will only return the file(s) content. To also get the filename it is necessary to access a nested Field instance which is indexed by the field name in the FieldStorage instance.
This script is a simplified version of the the one on the next page. This was done for didactic purposes only. Always use the one on the next page.
<html><body> <% if form.has_key('file') and form['file'].filename: # A nested Field object holds the file fileitem = form['file'] try: # Windows needs stdio set for binary mode. import msvcrt msvcrt.setmode (0, os.O_BINARY) # stdin = 0 msvcrt.setmode (1, os.O_BINARY) # stdout = 1 except ImportError: pass # strip leading path from file name to avoid directory traversal attacks fname = os.path.basename(fileitem.filename) # build absolute path to files directory dir_path = os.path.join(os.path.dirname(req.filename), 'files') open(os.path.join(dir_path, fname), 'wb').write(fileitem.file.read()) message = 'The file "%s" was uploaded successfully' % fname %> <p><%= message %></p> <p><a href="">Upload another file</a></p> <% else: # %> <form enctype="multipart/form-data" action="" method="post"> <p>File: <input type="file" name="file"></p> <p><input type="submit" value="Upload"></p> </form> <% # %> </body></html>
A directory traversal attack is one where the attacker submits a file with a leading path like in ../../attacker_program. This way he can save a program wherever the Apache user has write permission. Or read a file if the target script reads files.