Security Considerations for Optimistic Protocol Transitions in HTTP/1.1

Metadata

Publisher: IETF
Doc Type: Standard
Pages: 11
Abstract: In HTTP/1.1, the client can request a change to a new protocol on the existing connection. This document discusses the security considerations that apply to data sent by the client before this request is confirmed and adds new requirements to RFCs 9112 and 9298 to avoid related security issues.
Publication Date: 2026-03-01
Status Note: Proposed Standard
DOI: 10.17487/RFC9931
Link: https://doi.org/10.17487/RFC9931
Author(s): Benjamin M. Schwartz
Keyword(s): Request Smuggling, False Start, HTTP CONNECT

Latest version of IETF RFC 9931

Document Versions — IETF RFC 9931

▶ IETF RFC 9931 (2026-03-01)

THIS DOC [ACTIVE] [LATEST VERSION]

Normative Reference(s)

IETF RFC 2119 [Active*]
IETF RFC 8174 [Active*]
IETF RFC 9110 [Active*]
IETF RFC 9112 [Active*]
RFC9298 — RFC9298 EXTERNAL

Bibliographic Reference(s)

IANA, "Hypertext Transfer Protocol (HTTP) Upgrade Token Registry", <https://www.iana.org/assignments/http-upgrade-tokens/>. EXTERNAL
IETF RFC 2817 [Active*]
IETF RFC 6455 [Active*]
IETF RFC 8446 [Superseded*]
IETF RFC 9113 [Active*]
RFC9114 — RFC9114 EXTERNAL
RFC9484 — RFC9484 EXTERNAL

Source Data (JSON)

Full registry record with provenance metadata. Open directly: /api/doc/RFC9931.json

Reference Tree

Explore all references and references to this document, as a navigable tree.

Open Reference Tree

Reference this Doc

Plain text (ISO 690 compliant)

Preview:

IETF RFC 9931, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1. Available at https://doi.org/10.17487/RFC9931

Snippet:

IETF RFC 9931, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1. Available at https://doi.org/10.17487/RFC9931

HTML (ISO 690 compliant)

Preview:

IETF RFC 9931, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1. Available at https://doi.org/10.17487/RFC9931

Snippet:

<span class="citation"><cite>IETF RFC 9931</cite>, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1. Available at <a href="https://doi.org/10.17487/RFC9931" target="_blank" rel="noopener">https://doi.org/10.17487/RFC9931</a></span>

SMPTE's HTML Pub

Preview:

IETF RFC 9931, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1
doi: 10.17487/RFC9931
url: https://doi.org/10.17487/RFC9931

Snippet:

<li>
<cite id="bib-rfc9931">IETF RFC 9931</cite>, Security Considerations for Optimistic Protocol Transitions in HTTP/1.1
<span class="doi">10.17487/RFC9931</span>
</li>