CVE-2025-57804

Summary

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.

Affected Software

Weaknesses

• CWE-93: CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

CVE Program Container

Additional References

• https://lists.debian.org/debian-lts-announce/2025/09/msg00004.html

References

• https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h
• https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a

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