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[USN-8952-3] Tornado regression

Posted on 11 November 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8952-3
November 11, 2026

python-tornado regression
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 26.10
- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

USN-8952-2 introduced a regression in Tornado

Software Description:
- python-tornado: scalable, non-blocking web server and tools

Details:

USN-8952-2 fixed a regression in Tornado that broke static file serving
for applications that subclass Tornado's StaticFileHandler, such as
Jupyter. Unfortunately, that update's incomplete fix could introduce a regression by rejecting symlinks into system
directories like /usr/share, which distribution packages use for their
JavaScript and fonts, causing web UIs to return 403 errors. This update
fixes the problem.

We apologize for the inconvenience.

Original advisory details:

It was discovered that Tornado did not properly handle certain HTTP requests
and network inputs. An attacker could possibly use these issues to cause a
denial of service, expose sensitive information, or bypass access controls.

(CVE-2023-54397, CVE-2024-14029, CVE-2026-91990, CVE-2026-91992,
CVE-2026-103262, CVE-2026-103263)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 26.10
python3-tornado 6.5.5-5ubuntu1.3

Ubuntu 26.04 LTS
python3-tornado 6.5.4-0.1ubuntu0.4

Ubuntu 24.04 LTS
python3-tornado 6.4.0-1ubuntu0.8

Ubuntu 22.04 LTS
python3-tornado 6.1.0-3ubuntu0.1~esm8
Available with Ubuntu Pro

Ubuntu 20.04 LTS
python3-tornado 6.0.3+really5.1.1-3ubuntu0.1~esm9
Available with Ubuntu Pro

Ubuntu 18.04 LTS
python3-tornado 4.5.3-1ubuntu0.2+esm6
Available with Ubuntu Pro

Ubuntu 16.04 LTS
python3-tornado 4.2.1-1ubuntu3.1+esm6
Available with Ubuntu Pro

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-8952-3
https://ubuntu.com/security/notices/USN-8952-2
https://ubuntu.com/security/notices/USN-8952-1
https://launchpad.net/bugs/2172317
CVE-2026-103263

Package Information:
https://launchpad.net/ubuntu/+source/python-tornado/6.5.5-5ubuntu1.3
https://launchpad.net/ubuntu/+source/python-tornado/6.5.4-0.1ubuntu0.4
https://launchpad.net/ubuntu/+source/python-tornado/6.4.0-1ubuntu0.8

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