CVE-2025-57804
h2 allows HTTP Request Smuggling due to illegal characters in headers
- State
- Published
- Severity
- 6.9 Medium
- Published
- Aug 25, 2025
- Updated
- Nov 3, 2025
- Reserved
- Aug 20, 2025
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 6.9 Medium | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N | GitHub_M |
Weaknesses
- CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')
Affected Products
| Product | Versions |
|---|---|
h2python-hyper |
|
References
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