CVE-2025-57804

25.08.2025, 21:15

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.

CRLF Injection

Provider	Type	Base Score	Vector
NIST	NIST	UNKNOWN	---
GitHub_M	CNA	---	---
CISA-ADP	ADP	---	---

Awaiting analysis

This vulnerability is currently awaiting analysis.

Base Score

CVSS 3.x

EPSS Score

Percentile: 13%

Common Weakness Enumeration

CWE-93 - Improper Neutralization of CRLF Sequences ('CRLF Injection')
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

References

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

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