CVE-2025-57804

MEDIUM6.9

h2 allows HTTP Request Smuggling due to illegal characters in headers

Published Aug 25, 2025

Modified 4 months ago

Details

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.

References

WEB

https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a

WEB

https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h

WEB

https://lists.debian.org/debian-lts-announce/2025/09/msg00004.html

ADVISORY

https://www.cve.org/CVERecord?id=CVE-2025-57804

CVSS Analysis

CVSS v4.0

6.9