CVE-2025-57804

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.

Score

CVSS 4.0 6.9 Medium

Status

Deferred - security-advisories@github.com

Published

2025-08-25

Last modified

2025-11-03

Weaknesses

CWE-93

Affected products

• H2 (Python-hyper)

References

• https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a
• https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h
• https://lists.debian.org/debian-lts-announce/2025/09/msg00004.html