Announcing Tornado 6.5.9

[Ben Darnell]

Tornado 6.5.9 is now available on PyPI. This is a security release which restricts symlink traversal in StaticFileHandler and fixes several denial-of-service vulnerabilities. 

https://www.tornadoweb.org/en/stable/releases/v6.5.9.html

What’s new in Tornado 6.5.9¶

Sep 14, 2026¶

Security fixes¶

• StaticFileHandler no longer follows symlinks outside of the static root directory. Applications that wish to continue the previous behavior may set the new argument allowed_symlink_directory to the directory (an ancestor of the static root) that should be used for symlink validation. Thanks to afldl and iaokhut-from-NightWolf-Team for reporting this issue.

• curl_httpclient has a new max_body_size argument (default 100MB, same as for simple_httpclient). This limit is enforced on all requests, whether or not streaming_callback is used. curl_httpclient now also controls its memory usage when decompressing response bodies. Thanks to afldl, iaohkut-from-NightWolf-Team, and aoto-tech for reporting this issue.

• simple_httpclient now correctly applies the max_body_size limit to responses using HTTP/1.0 format (no Content-Length or Transfer-Encoding). Previously it silently truncated such responses at max_buffer_size instead. Thanks to afldl for reporting this issue.

• simple_httpclient now rejects responses that use more than 10 100 Continue responses, which could previously cause stack overflow errors. Thanks to afldl for reporting this issue.

• The limit ParseBodyConfig.urlencoded.max_argument is now applied to URL arguments in addition to POST bodies. Thanks to iaohkut-from-NightWolf-Team, afldl, and manus-pi for reporting this issue.

Bug fixes¶

tornado.iostream¶

• .IOStream.read_until_close now reports errors correctly when a stream is closed due to an error or exceeds a memory limit. Previously it would report a successful read of whatever was in the buffer. Connection resets are still treated as a normal close (as they are elsewhere in IOStream), since some platforms report a clean shutdown by the peer this way.