CVE-2026-71554

MediumCVSS 5.3/10Last modified Oct 24, 2026

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.

Metrics

CVSS 3.1 5.3/10CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Weakness enumeration

CWE-444

Affected software

No affected versions have been published.

Timeline

Published: Aug 6, 2026
Last modified: Oct 24, 2026
NVD status: Deferred

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