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gh-142412: Add warning about urlsplit's netloc parsing and open redirects #144448

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gh-142412: Add warning about urlsplit's netloc parsing and open redirects #144448

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11 changes: 11 additions & 0 deletions Doc/library/urllib.parse.rst
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Expand Up @@ -530,6 +530,17 @@
sense? Is that a sensible ``path``? Is there anything strange about that
``hostname``? etc.

.. warning::
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@picnixz picnixz Feb 3, 2026

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It does not make sense to have a warning note here. In addition, its placing interrupts the flow of the current text and is quite off-topic here.


:func:`urlsplit` (and :func:`urlparse`) does not consider a URL's

Check warning on line 535 in Doc/library/urllib.parse.rst

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py:attr reference target not found: urllib.parse.SplitResult.netloc [ref.attr]
:attr:`~urllib.parse.SplitResult.netloc` to be present unless
it is preceded by ``//``. This means that, for example, the URL
``///example.com/path`` will be parsed with an empty ``netloc`` and a
``path`` of ``/example.com/path``. This behavior may lead to open redirect
vulnerabilities in applications that rely on checking the ``netloc`` to
validate redirect URLs. Always carefully validate redirect targets,
preferably using an allowlist of known-safe URLs or hosts.

What constitutes a URL is not universally well defined. Different applications
have different needs and desired constraints. For instance the living `WHATWG
spec`_ describes what user facing web clients such as a web browser require.
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