CVE-2026-71554

Name	CVE-2026-71554
Description	h2 is a pure-Python implementation of a HTTP/2 protocol stack. Versions up to and including 4.4.0 accept request header blocks containing more than one Host header, and forward every Host header to the consuming application. Where the consumer downgrades HTTP/2 to HTTP/1.1, the resulting request carries two Host header lines, providing a request smuggling primitive. This issue is fixed in version 4.4.1.
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)

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	vulnerable
	bookworm	4.1.0-4	vulnerable
	trixie	4.2.0-1	vulnerable
	forky, sid	4.3.0-2	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	(unstable)	(unfixed)

Notes

https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg
Fixed by: https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6 (4.4.1)