CVE-2025-57804

Name	CVE-2025-57804
Description	h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DLA-4290-1
Debian Bugs	1112348

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
python-h2 (PTS)	bullseye	4.0.0-3	vulnerable
	bullseye (security)	4.0.0-3+deb11u1	fixed
	bookworm	4.1.0-4	vulnerable
	forky, sid, trixie	4.2.0-1	vulnerable

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

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
python-h2	source	bullseye	4.0.0-3+deb11u1		DLA-4290-1
python-h2	source	(unstable)	(unfixed)			1112348

Notes

[trixie] - python-h2 <no-dsa> (Minor issue)
[bookworm] - python-h2 <no-dsa> (Minor issue)
https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h
https://github.com/python-hyper/h2/commit/883ed37be42592b2f0aa0caddab6ca5e3d668fa3 (v4.3.0)
https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a (v4.3.0)