CVE-2025-57804

h2 allows HTTP Request Smuggling due to illegal characters in headers

Published: Aug 25, 2025Updated: Nov 3, 2025 Sources: CVE List NVD GHSA BDUCWE-93

5.3MEDIUM

Description

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAccess Vector

Network

AC:LAccess Complexity

Low

Impact

C:NConfidentiality

None

I:LIntegrity

A:NAvailability

None

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Weaknesses

CWE-93

Affected Products

python-hyper

oss-project

h2Library

OSS Libraries / generic-library

ООО «РусБИТех-Астра»

commercial·RUaka rusbitech-astra

Astra Linux Special EditionOn-premOS

Operating Systems / linux-distro

Python Software Foundation

oss-project·USaka psf

Python-h2LibraryLibrary

OSS Libraries

PyPI

package-ecosystem

OSS Libraries

Exploitability

Official Patch Available

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References

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

github.com

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

github.com

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

lists.debian.org

and 9 more references View all →

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