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fix: preserve original URL string in Location header to prevent percent-encoding corruption (#5319) #13357

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fix: preserve original URL string in Location header to prevent percent-encoding corruption (#5319) #13357

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fix: preserve original URL string in Location header to prevent perce…
waterWang Aug 9, 2026
004c9e5
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Aug 9, 2026
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1 change: 1 addition & 0 deletions CHANGES/5319.bugfix.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Fixed a bug where server-side redirects (``HTTPFound`` and other ``HTTPMove`` subclasses) re-encoded percent-encoded characters (e.g. ``%3F`` for ``?``) in the ``Location`` header, which could break the redirected webserver when the URL contained a query string argument that was itself a URL. The ``Location`` header now preserves the original location string (CR/LF stripped for header-injection safety) while the ``location`` property still returns the parsed ``URL``.
11 changes: 8 additions & 3 deletions aiohttp/web_exceptions.py
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Expand Up @@ -231,12 +231,17 @@ def __init__(
super().__init__(
headers=headers, reason=reason, text=text, content_type=content_type
)
self._location = URL(location)
self.headers["Location"] = str(self.location)
self._parsed_location = URL(location)
# Preserve the original location string for the Location header so that
# percent-encoded characters (e.g. "%3F" for "?") are not re-encoded by
# yarl.URL (which decodes them and can break the redirected webserver).
# Only strip CR/LF to prevent request-smuggling-style header injection;
# the URL is still validated via URL(location) above.
self.headers["Location"] = str(location).replace("\r", "").replace("\n", "")

@property
def location(self) -> URL:
return self._location
return self._parsed_location


class HTTPMultipleChoices(HTTPMove):
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