Python Hyper H2 vulnerabilities

2 vulnerabilities

Known vulnerabilities in Python Hyper H2, newest first, with CVSS severity, EPSS, KEV listings, ransomware use and the affected versions.

6.9CVE-2025-57804chainguardairflow-2+26
EPSS score
1.73%
h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.5.3CVE-2026-71554chainguardairflow-2+32
EPSS score
0.42%
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.