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Ubuntu 25.10: Critical DoS Regression in python-urllib3 USN-7927-3

ubuntu
Calendar Grey January 13, 2026
Dist Ubuntu Esm H88
A regression in python-urllib3 affects Ubuntu; fix to prevent denial of service due to overuse of resources.
USN-7927-1 introduced a regression in urllib3

Summary

USN-7927-1 introduced a regression in urllib3

Software Description:

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

Details:

USN-7927-1 fixed vulnerabilities in urllib3. The update for CVE-2025-66471

introduced a regression in urllib3 when decompressing zstd data. This

update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Illia Volochii discovered that urllib3 did not limit the steps in a

decompression chain. An attacker could possibly use this issue to cause

urllib3 to use excessive resources, causing a denial of service.

(CVE-2025-66418)

Rui Xi discovered that urllib3 incorrectly handled highly compressed data.

An attacker could possibly use this issue to cause urllib3 to use

excessive resources, causing a denial of service. This issue only affected

Ubuntu 24.04 LTS, Ubuntu 25.04, and Ubuntu 25.10. (CVE-2025-66471)

For the brotli encoding, the fix for CVE-2025-66471 requires an additional

security update in t...

Read the Full Advisory

Topics%20covered

Topics Covered

security advisory denial of service critical bug fix Ubuntu python-urllib3

Update Instructions

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

Ubuntu 25.10
  python3-urllib3                 2.3.0-3ubuntu0.4

Ubuntu 25.04
  python3-urllib3                 2.3.0-2ubuntu0.5

Ubuntu 24.04 LTS
  python3-urllib3                 2.0.7-1ubuntu0.6

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

References

https://ubuntu.com/security/notices/USN-7927-3

https://ubuntu.com/security/notices/USN-7927-2

https://ubuntu.com/security/notices/USN-7927-1

CVE-2025-66471,

Severity
critical
Lowest
Low
Medium
High
Critical

Ubuntu Security Notice USN-7927-3

Topics%20covered

Topics Covered

security advisory denial of service critical bug fix Ubuntu python-urllib3

Package Information

https://launchpad.net/ubuntu/+source/python-urllib3/2.3.0-2ubuntu0.5

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