CVE-2026-71554
MEDIUM
NVD
CVSS Score
5.3
Severity
MEDIUM
Published
Aug 06, 2026
Vendor
unknown
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.