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. If it does not 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.
<html><body> <form enctype="multipart/form-data" action="save_file.py" method="post"> <p>File: <input type="file" name="file"></p> <p><input type="submit" value="Upload"></p> </form> </body></html>
The getfirst() and getlist() methods will only return the file(s) content. To also get the filename it is necessary to access a nested FieldStorage instance by its index in the top FieldStorage instance.
#!/usr/bin/env python import cgi, os import cgitb; cgitb.enable() 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 form = cgi.FieldStorage() # A nested FieldStorage instance holds the file fileitem = form['file'] # Test if the file was uploaded if fileitem.filename: # strip leading path from file name to avoid directory traversal attacks fn = os.path.basename(fileitem.filename) open('files/' + fn, 'wb').write(fileitem.file.read()) message = 'The file "' + fn + '" was uploaded successfully' else: message = 'No file was uploaded' print """\ Content-Type: text/html\n <html><body> <p>%s</p> </body></html> """ % (message,)
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.