CVE-2026-71554

Published: Aug 6, 2026Modified: Aug 8, 2026

5.3

Vector

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

Exploitability: 3.9 / Impact: 1.4

Source: security-advisories@github.com (Secondary)

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.

Related CWEs

CWE-444

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

References (2)

https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6

Source: security-advisories@github.com

https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg

Source: security-advisories@github.com

Timeline

No history available yet.