CVE-2025-66418

Publication date 5 December 2025

Last updated 11 December 2025

Ubuntu priority

Description

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

Read the notes from the security team

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-urllib3	25.10 questing	Fixed 2.3.0-3ubuntu0.1
	25.04 plucky	Fixed 2.3.0-2ubuntu0.2
	24.04 LTS noble	Fixed 2.0.7-1ubuntu0.3
	22.04 LTS jammy	Fixed 1.26.5-1~exp1ubuntu0.4
	20.04 LTS focal	Fixed 1.25.8-2ubuntu0.4+esm2
	18.04 LTS bionic	Not affected
	16.04 LTS xenial	Not affected
	14.04 LTS trusty	Not affected
python-pip	25.10 questing	Vulnerable
	25.04 plucky	Vulnerable
	24.04 LTS noble	Vulnerable
	22.04 LTS jammy	Vulnerable
	20.04 LTS focal	Vulnerable
	18.04 LTS bionic	Not affected
	16.04 LTS xenial	Not affected
	14.04 LTS trusty	Not affected

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Notes

mdeslaur

On focal and earlier, the python-pip package bundles python-urllib3 binaries when built. After updating python-urllib3, a no-change rebuild of python-pip is required. On jammy and later, python-urllib3 is bundled in the python-pip package and needs to be patched.

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
python-urllib3	Upstream: 24d7b67

References

Related Ubuntu Security Notices (USN)

USN-7927-1
urllib3 vulnerabilities
11 December 2025