CVE-2025-66418

Name	CVE-2025-66418
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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-4421-1
Debian Bugs	1122030

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-urllib3 (PTS)	bullseye	1.26.5-1~exp1	vulnerable
	bullseye (security)	1.26.5-1~exp1+deb11u2	fixed
	bookworm	1.26.12-1+deb12u1	vulnerable
	trixie	2.3.0-3	vulnerable
	forky, sid	2.5.0-1	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-urllib3	source	bullseye	1.26.5-1~exp1+deb11u2		DLA-4421-1
python-urllib3	source	(unstable)	(unfixed)			1122030

Notes

https://www.openwall.com/lists/oss-security/2025/12/05/4
https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53
Fixed by: https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8 (2.6.0)