https://github.com/python/cpython/commit/d6bcc154e93a0a20ab97187d3e8b726fffb14f8f
commit: d6bcc154e93a0a20ab97187d3e8b726fffb14f8f
branch: main
author: Alex Gaynor <[email protected]>
committer: alex <[email protected]>
date: 2024-11-15T18:09:05-05:00
summary:
Added a warning to the urljoin docs, indicating that it is not safe to use with
attacker controlled URLs (GH-126659)
This was flagged to me at a party today by someone who works in red-teaming as
a frequently encountered footgun. Documenting the potentially unexpected
behavior seemed like a good place to start.
files:
M Doc/library/urllib.parse.rst
diff --git a/Doc/library/urllib.parse.rst b/Doc/library/urllib.parse.rst
index 0501dc8733b2cd..44a9c79cba2216 100644
--- a/Doc/library/urllib.parse.rst
+++ b/Doc/library/urllib.parse.rst
@@ -407,6 +407,15 @@ or on combining URL components into a URL string.
If you do not want that behavior, preprocess the *url* with
:func:`urlsplit` and
:func:`urlunsplit`, removing possible *scheme* and *netloc* parts.
+ .. warning::
+
+ Because an absolute URL may be passed as the ``url`` parameter, it is
+ generally **not secure** to use ``urljoin`` with an attacker-controlled
+ ``url``. For example in,
+ ``urljoin("https://website.com/users/";, username)``, if ``username`` can
+ contain an absolute URL, the result of ``urljoin`` will be the absolute
+ URL.
+
.. versionchanged:: 3.5
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