CVE-2026-71554
Published:August 06, 2026
Updated:August 31, 2026
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 Packages
h2 (CONDA):
Affected version(s) >=2.6.2 <4.4.1Fix Suggestion:
Update to version 4.4.1h2 (CONDA):
Affected version(s) >=2.6.2 <4.4.1Fix Suggestion:
Update to version 4.4.1https://github.com/python-hyper/h2.git (GITHUB):
Affected version(s) >=v1.0.0 <v4.4.1Fix Suggestion:
Update to version v4.4.1h2 (PYTHON):
Affected version(s) >=0.1.0 <4.4.1Fix Suggestion:
Update to version 4.4.1h2 (PYTHON):
Affected version(s) >=0.1.0 <4.4.1Fix Suggestion:
Update to version 4.4.1Related Resources (7)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.9
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
LOW
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
LOW
Weakness Type (CWE)
Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
EPSS
Base Score:
0.44