← CVE Intelligence

CVE-2026-71554

h2: Duplicate Host header could facilitate request smuggling PUBLISHED

Description (CNA)

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.

Affected (CNA)

Vendor / productVersions
python-hyper / h2affected < 4.4.1

CWE

CWE-444

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.