CVE-2025-43859

Name	CVE-2025-43859
Description	h11 is a Python implementation of HTTP/1.1. Prior to version 0.16.0, a leniency in h11's parsing of line terminators in chunked-coding message bodies can lead to request smuggling vulnerabilities under certain conditions. This issue has been patched in version 0.16.0. Since exploitation requires the combination of buggy h11 with a buggy (reverse) proxy, fixing either component is sufficient to mitigate this issue.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1104056

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-h11 (PTS)	bullseye	0.12.0-1	fixed
	sid, trixie, bookworm	0.14.0-1	vulnerable

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-h11	source	bullseye	(not affected)
python-h11	source	(unstable)	(unfixed)			1104056

Notes

[bullseye] - python-h11 <not-affected> (Vulnerable code introduced later)
https://github.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfj
Introduced by: https://github.com/python-hyper/h11/commit/26ec787d44aacbff8fbc0fc1af7e3213dd993d46 (v0.14.0)
Fixed by: https://github.com/python-hyper/h11/commit/dff7cc397a26ed4acdedd92d1bda6c8f18a6ed9f (v0.16.0)