CVE-2025-57804

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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Weakness Type (CWE)

CWE-93 CWE-93

References

Other 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

Frequently Asked Questions

What is 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.

How do I check if I'm vulnerable to CVE-2025-57804? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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