Hi,

I find this regex '(?:^|,)[ \t]*([^ \t]+)[ \t]+' may be stucked by input.

The vulnerable regex is located in https://github.com/python/cpython/blob/5c5a938573ce665f00e362c7766912d9b3f3b44e/Lib/urllib/request.py#L946

The ReDOS vulnerability of the regex is mainly due to the sub-pattern ',([^ \t]+)' and can be exploited with the following string
attack_str = "," * 10000

You can execute redos_python.py to reproduce the ReDos vulnerability.


I am willing to suggest that you replace '(?:^|,)[ \t]*([^ \t]+)[ \t]+' with '(?:^|,)[ \t]*([^ \t,]+)[ \t]+'

Looking forward for your response​!

Best,
Yeting Li