Tags: tornadoweb/tornado
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What's new in Tornado 6.5.7 Jun 8, 2026 ----------- Security fixes ~~~~~~~~~~~~~~ - ``CurlAsyncHTTPClient`` now fully resets the curl object before reusing it. This prevents incorrectly reusing options from a previous request, specifically including client SSL and credentials used for accessing proxies. Thanks to `Koh Jun Sheng <https://github.com/seankohjs>`_ for reporting this issue.
What's new in Tornado 6.5.6 May 27, 2026 ------------ Security fixes ~~~~~~~~~~~~~~ - ``SimpleAsyncHTTPClient`` now strips the ``Authorization`` and ``Cookie`` headers from the request when following a redirect to a different origin. This matches the default behavior of ``CurlAsyncHTTPClient``. Applications that need different behavior here can set ``follow_redirects=False`` and handle redirects manually. Thanks to [Yannick Wang](https://github.com/noobone123) for being first to report this issue, as well as additional reporters [Kai Aizen](https://github.com/SnailSploit), [HunSec](https://github.com/0xHunSec), and [Thai Son Dinh](https://github.com/sondt99). - ``SimpleAsyncHTTPClient`` now enforces ``max_body_size`` on the decompressed size of the response, rather than the compressed size. This prevents a denial-of-service attack via a very large compressed response. Thanks to [Yuichiro Kedashiro](https://github.com/yuui25) for reporting this issue. - Fixed a bug in the C extension that could have read up to three bytes past the end of an input array. Thanks to [Thai Son Dinh](https://github.com/sondt99) for reporting this issue. - ``OpenIDMixin`` has improved parsing for the ``check_authentication`` response. Thanks to [Yannick Wang](https://github.com/noobone123) for reporting this issue. Bug fixes ~~~~~~~~~ - ``CurlAsyncHTTPClient`` has been updated to use non-deprecated APIs, avoiding deprecation warnings with recent versions of ``pycurl``.
What's new in Tornado 6.5.5 Mar 10, 2026 ------------ Security fixes ~~~~~~~~~~~~~~ - ``multipart/form-data`` requests are now limited to 100 parts by default, to prevent a denial-of-service attack via very large requests with many parts. This limit is configurable via `tornado.httputil.ParseMultipartConfig`. Multipart parsing can also be disabled completely if not required for the application. Thanks to [0x-Apollyon](https://github.com/0x-Apollyon) and [bekkaze](https://github.com/bekkaze) for reporting this issue. - The ``domain``, ``path``, and ``samesite`` arguments to `.RequestHandler.set_cookie` are now validated for illegal characters, which could be abused to inject other attributes on the cookie. Thanks to Dhiral Vyas (Praetorian) for reporting this issue. - Carriage return characters are no longer accepted in ``multipart/form-data`` headers. Thanks to [sergeykochanov](https://github.com/sergeykochanov) for reporting this issue.
What's new in Tornado 6.5.4 Dec 15, 2025 ------------ Bug fixes ~~~~~~~~~ - The ``in`` operator for ``HTTPHeaders`` was incorrectly case-sensitive, causing lookups to fail for headers with different casing than the original header name. This was a regression in version 6.5.3 and has been fixed to restore the intended case-insensitive behavior from version 6.5.2 and earlier.
What's new in Tornado 6.5.3 Dec 10, 2025 ------------ Security fixes ~~~~~~~~~~~~~~ - Fixed a denial-of-service vulnerability involving quadratic computation when parsing ``multipart/form-data`` request bodies. `CVE-2025-67726 <https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8>`_ Thanks to `Finder16 <https://github.com/Finder16>`_ for reporting this issue. - Fixed a denial-of-service vulnerability involving quadratic computation when parsing repeated HTTP headers. `CVE-2025-67725 <https://github.com/tornadoweb/tornado/security/advisories/GHSA-c98p-7wgm-6p64>`_. Thanks to `Finder16 <https://github.com/Finder16>`_ for reporting this issue. - Fixed a header injection and XSS vulnerability involving the ``reason`` argument to `.RequestHandler.set_status` and `tornado.web.HTTPError`. `CVE-2025-67724 <https://github.com/tornadoweb/tornado/security/advisories/GHSA-pr2v-jx2c-wg9f>`_. Thanks to `Finder16 <https://github.com/Finder16>`_ and `Cheshire1225 <https://github.com/Cheshire1225>`_ for reporting this issue. Demo changes ~~~~~~~~~~~~ - Several demo applications bundled with the Tornado repo (``blog``, ``chat``, ``facebook``) had an open redirect vulnerability which has been fixed. This is not covered by a CVE or security advisory since the demo applications are not included as a part of the Tornado package when installed, but developers who have copied code from these demos may which to review their own applications for open redirects. Thanks to `J1vvoo <https://github.com/J1vvoo>`_ for reporting this issue. - The ``s3server`` demo application contained some path traversal vulnerabilities. Since this demo application was not demonstrating any interesting aspects of Tornado, it has been deleted rather than being fixed. Thanks to `J1vvoo <https://github.com/J1vvoo>`_ for reporting this issue.
What's new in Tornado 6.5.2 Aug 8, 2025 ----------- Bug fixes ~~~~~~~~~ - Fixed a bug that resulted in WebSocket pings not being sent at the configured interval. - Improved logging for invalid ``Host`` headers. This was previouisly logged as an uncaught exception with a stack trace, now it is simply a 400 response (logged as a warning in the access log) - Restored the ``host`` argument to ``.HTTPServerRequest``. This argument is deprecated and will be removed in the future, but its removal with no warning in 6.5.0 was a mistake. - Removed a debugging print statement that was left in the code. - Improved type hints for ``gen.multi``.
What's new in Tornado 6.5.0 May 15, 2025 ------------ Security Improvements ~~~~~~~~~~~~~~~~~~~~~ - Previously, malformed ``multipart-form-data`` requests could log multiple warnings and constitute a denial-of-service attack. Now an exception is raised at the first error, so there is only one log message per request. This fixes `CVE-2025-47287 <https://github.com/tornadoweb/tornado/security/advisories/GHSA-7cx3-6m66-7c5m>`_. General Changes ~~~~~~~~~~~~~~~ - Python 3.14 is now supported. Older versions of Tornado will work on Python 3.14 but may log deprecation warnings. - The free-threading mode of Python 3.13 is now supported on an experimental basis. Prebuilt wheels are not yet available for this configuration, but it can be built from source. - The minimum supported Python version is 3.9. Deprecation Notices ~~~~~~~~~~~~~~~~~~~ - Support for ``obs-fold`` continuation lines in HTTP headers is deprecated and will be removed in Tornado 7.0, as is the use of carriage returns without line feeds as header separators. - The ``callback`` argument to `.websocket_connect` is deprecated and will be removed in Tornado 7.0. Note that ``on_message_callback`` is not deprecated. - The ``log_message`` and ``args`` attributes of `tornado.web.HTTPError` are deprecated. Use the new ``get_message`` method instead. Type Annotation Changes ~~~~~~~~~~~~~~~~~~~~~~~ - `tornado.concurrent.chain_future` is now typed as accepting both asyncio and concurrent Futures. - `tornado.gen.multi` and ``multi_future`` now take ``Sequences`` and ``Mappings`` instead of ``List`` and ``Dict``. - `tornado.httputil.RequestStartLine` and `.ResponseStartLine` now have type annotations for their attributes. - `.HTTPHeaders` now has type annotations for its elements. - The ``autoescape`` argument to `tornado.template.BaseLoader` is now marked as optional. - ``tornado.routing._RuleList`` is now a ``Sequence`` for more flexibility. - ``.RequestHandler.SUPPPORTED_METHODS`` is now typed to support overriding in a subclass. - Types for `.RequestHandler.get_body_argument` and ``get_query_argument`` are improved and now match the ``get_argument`` method. - `.RequestHandler.get_cookie` now has more accurate types. - The return type of `.UIModule.render` may now be either `str` or `bytes`. `tornado.httputil` ~~~~~~~~~~~~~~~~~~ - Support for ``obs-fold`` continuation lines in HTTP headers is deprecated and will be removed in Tornado 7.0, as is the use of carriage returns without line feeds as header separators. - Request start lines may no longer include control characters. - Method names containing invalid characters now return error code 400 instead of 405. - Header names are now restricted to the set of characters permitted by the RFCs. - Control characters are no longer allowed in (incoming) header values. - Handling of trailing whitespace in headers has been improved, especially with ``obs-fold`` continuation lines. - The ``Host`` header is now restricted to the set of characters permitted by the RFCs. It is now an error to send more than one ``Host`` header, or to omit a ``Host`` header for a request that is not using HTTP/1.0. `tornado.ioloop` ~~~~~~~~~~~~~~~~ - Fixed a bug in which `contextvars` that were set when the event loop was created were not available inside the event loop on Windows. `tornado.netutil` ~~~~~~~~~~~~~~~~~ - `.bind_unix_socket` now supports the Linux abstract namespace. `tornado.platform.twisted` ~~~~~~~~~~~~~~~~~~~~~~~~~~ - ``TwistedResolver`` has been deleted. It was already deprecated and scheduled for removal in Tornado 7.0, but due to the adoption of RFC 8482 it no longer works for most domain names. This class was primarily intended to provide thread-free non-blocking DNS resolution. If that is still required, ``tornado.platform.caresresolver`` is the next best option, although it has its own limitations which differ from TwistedResolver, and it is also deprecated. Most users should switch to the default resolver, which uses threads. `tornado.web` ~~~~~~~~~~~~~ - The set of characters allowed in (outgoing) HTTP headers now matches the RFCs. Specifically, tab characters are now allowed and DEL is not. - Invalid ``If-Modified-Since`` headers are now ignored instead of causing a 500 error. - ``%`` characters in the log message of `tornado.web.HTTPError` are no longer doubled when no additional arguments are passed. This matches the behavior of `logging.LogRecord`. A new method ``get_message`` has been added to ``HTTPError`` to allow access to the fully-substituted message; directly accessing ``log_message`` and ``args`` is deprecated. `tornado.websocket` ~~~~~~~~~~~~~~~~~~~ - Some bugs involving ``ping_interval`` and ``ping_timeout`` have been fixed. Setting the ``ping_timeout`` greater than the ``ping_interval`` is no longer supported. The default ``ping_timeout`` is now equal to the ``ping_interval``. - The ``callback`` argument to ``websocket_connect`` is deprecated and will be removed in Tornado 7.0. Note that ``on_message_callback`` is not deprecated.
What's new in Tornado 6.4.2 Nov 21, 2024 ------------ Security Improvements ~~~~~~~~~~~~~~~~~~~~~ - Parsing of the cookie header is now much more efficient. The older algorithm sometimes had quadratic performance which allowed for a denial-of-service attack in which the server would spend excessive CPU time parsing cookies and block the event loop. This change fixes CVE-2024-7592.
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