CVE-2025-57804
Unknown Unknown - Not Provided
BaseFortify

Publication date: 2025-08-25

Last updated on: 2025-11-03

Assigner: GitHub, Inc.

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.
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Meta Information
Published
2025-08-25
Last Modified
2025-11-03
Generated
2026-06-16
AI Q&A
2025-08-26
EPSS Evaluated
2026-06-14
NVD
CVE-2025-57804
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
python-hyper h2 4.0
python-hyper h2 4.3.0
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-93 The product 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.
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Executive Summary

This vulnerability exists in the h2 Python HTTP/2 protocol stack before version 4.3.0. It allows attackers to perform HTTP request smuggling by injecting CRLF characters into headers. When servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names and values, attackers can manipulate request boundaries and bypass security controls.

Impact Analysis

The vulnerability can allow attackers to smuggle HTTP requests, potentially bypassing security controls. This can lead to unauthorized access, manipulation of requests, and other security issues depending on the server's handling of HTTP requests.

Mitigation Strategies

Upgrade the h2 library to version 4.3.0 or later, as this version contains the patch that fixes the HTTP/2 request splitting vulnerability. Until the upgrade is applied, consider monitoring and filtering HTTP/2 traffic for suspicious CRLF injection attempts, and avoid downgrading HTTP/2 requests to HTTP/1.1 without proper validation of header names and values.

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