Hi, During my recent tests I have discovered that the urllib http client (urllib.request.urlopen()) is vulnerable to DOS attack using a simple but effective trick.

I am attaching a file named server.py download it and run it using latest version of python. After running it execute the following python code in python interactive mode. (python -i)

import urllib.request
request = urllib.request.Request('http://127.0.0.1:1338')
response = urllib.request.urlopen(req, timeout=1)

DOS limit: We can achieve DOS for unlimited time.
 
How to fix?
Implement a good logic for timeout in urllib.request.urlopen(url, timeout). Timeout value should not be reset after client receives a data(bytes), because it can easily be abused to achieve DOS.