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[USN-7955-2] urllib3 regression

Posted on 19 January 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-7955-2
January 19, 2026

python-urllib3 regression
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS

Summary:

USN-7955-1 introduced a regression in urllib3

Software Description:
- python-urllib3: HTTP library with thread-safe connection pooling

Details:

USN-7955-1 fixed vulnerabilities in urllib3. The update introduced a
regression in response streaming on Ubuntu 20.04 LTS and Ubuntu 22.04 LTS.
This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

It was discovered that urllib3 incorrectly handled decompression during
HTTP redirects. An attacker could possibly use this issue to cause urllib3
to use excessive resources, causing a denial of service.

Update instructions:

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

Ubuntu 22.04 LTS
python3-urllib3 1.26.5-1~exp1ubuntu0.6

Ubuntu 20.04 LTS
python3-urllib3 1.25.8-2ubuntu0.4+esm4
Available with Ubuntu Pro

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

References:
https://ubuntu.com/security/notices/USN-7955-2
https://ubuntu.com/security/notices/USN-7955-1
CVE-2026-21441, https://bugs.launchpad.net/bugs/2138420

Package Information:
https://launchpad.net/ubuntu/+source/python-urllib3/1.26.5-1~exp1ubuntu0.6

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