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.

How to fix CVE-2025-57804

To remediate CVE-2025-57804, upgrade the affected package to a fixed version below.

• —upgrade to 4.0.0-3+deb11u1 or later
• —upgrade to 4.0.0-3+deb11u1 or later
• —upgrade to 4.3.0 or later

Is CVE-2025-57804 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 4.0.0-3+deb11u1
• from 0, < 4.0.0-3+deb11u1
• from 0, < 4.3.0

CVSS scores

References (6)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2025-57804
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2025-57804
• PATCHgithub.com/python-hyper/h2
• WEBgithub.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a