Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

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CVE-2025-57804

Severity CVSS v4.0:
MEDIUM
Type:
CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')
Publication date:
25/08/2025
Last modified:
15/04/2026

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.

Impact

Vector 4.0
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 CVSS v4.0 Severity and Metrics:

Base Score: 6.90 MEDIUM
Vector: 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

Attack Vector (AV): Network
Attack Complexity (AC): Low
Attack Requirements (AT): None
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): None
Integrity (VI): None
Availability (VA): None
Confidentiality (SC): None
Integrity (SI): Low
Availability (SA): None

Base Score 4.0
6.90
Severity 4.0
MEDIUM

References to Advisories, Solutions, and Tools