Re: HTTP/1.1 Request Smuggling Defense using Cryptographic Message Binding (new draft)

I think this draft identifies a real problem, but I'm not convinced that this is the right solution.

As a defense against request smuggling, this header is only a partial defense:
1.Both parties must upgrade their software to benefit.  This is a particularly serious limitation because the relevant parties are specifically those with limited ability to upgrade their software (otherwise they would be using HTTP/2).
2. Not all known parser confusion attacks are prevented, as noted by others in this thread.
3. It's not clear how to use it without TLS.  TLS may not be in use when the intermediary and backend are inside a single deployment (or even a single host!).

There are many other strategies that we could explore that would be easier to deploy and/or more effective.

A. Declare a limitation on the reuse of HTTP/1.1 connections, similar to draft-ietf-httpbis-optimistic-upgrade.  For example, this might say "when speaking to a potentially vulnerable server, an intermediary MUST NOT reuse a single HTTP/1.1 connection for requests from multiple clients (unless they are mutually trusting)".  This reduces efficiency, but anyone who cares about efficiency shouldn't be using HTTP/1.1.
B. Confirm the HTTP/1.1 parser state between requests.  For example, an intermediary could inject a request like "TRACE /.well-known/barrier/$random HTTP/1.1" after each forwarded request, and check that the TRACE response is received correctly before forwarding the next request.
C. Document a simple profile of HTTP/2 (e.g. SETTINGS_HEADER_TABLE_SIZE=0, SETTINGS_MAX_CONCURRENT_STREAMS=1, etc.)
D. Define new header fields to demarcate the header section (e.g. "Begin-Headers: (unpredictable value) ... End-Headers: (same value)").  This could be extended to cross-check the header in various ways (e.g. enumerating the payload length of each header field).

--Ben
________________________________
From: Erik Nygren <nygren@gmail.com>
Sent: Sunday, October 19, 2025 12:18 PM
To: ietf-http-wg@w3.org Group <ietf-http-wg@w3.org>
Subject: HTTP/1.1 Request Smuggling Defense using Cryptographic Message Binding (new draft)

I've submitted a new -00 draft for draft-nygren-httpbis-http11-request-binding: HTTP/1. 1 Message Binding adds new hop-by-hop header fields that are cryptographically bound to requests and responses. The keys used are negotiated out-of-band

I've submitted a new -00 draft for draft-nygren-httpbis-http11-request-binding:

   HTTP/1.1 Message Binding adds new hop-by-hop header fields that are
   cryptographically bound to requests and responses.  The keys used are
   negotiated out-of-band from the HTTP datastream (such as via TLS
   Exporters).  These header fields allow endpoints to detect and
   mitigate desynchronization attacks, such as HTTP Request Smuggling,
   that exist due to datastream handling differences.

While it would be great if the entire world could switch to HTTP/2 and HTTP/3,
that just isn't feasible as there are legacy HTTP/1.1 clients that need to be supported, as well as a large ecosystem of HTTP/1.1 Intermediaries and Origin Servers.

This proposal provides a hop-by-hop defense mechanism that allows endpoints
to defend HTTP/1.1 traffic against Request Smuggling attacks without fundamentally changing the HTTP/1.1 protocol, and in a way which can hopefully drop-in to auto-negotiate and "just work" to provide defenses.  There are still quite a few different directions we could take the design, as discussed briefly in the draft, as well as some open issues around how particular details get implemented.

Note that this is focused on H1.  While H2 and H3 have streamids and other ways to convey information out-of-band, H1 lacks those.  You can see this as a way of getting stream ID equivalents into H1 in a protected but minimally invasive manner.

I'm looking forward to discussing this in Montreal in two weeks to see if this is something that other implementers (especially of Intermediaries and Origin Servers) would be  interested in.  I'd also be thrilled to add in one or more co-authors as this adds the most value if it is implemented and deployed by as many vendors and open source projects as possible.

Best, Erik



[try #3 at sending to the list, this time with a different email address]

---------- Forwarded message ---------
From: <internet-drafts@ietf.org<mailto:internet-drafts@ietf.org>>
Date: Thu, Oct 16, 2025 at 6:23 PM
Subject: New Version Notification for draft-nygren-httpbis-http11-request-binding-00.txt
To: Erik Nygren <erik+ietf@nygren.org<mailto:erik%2Bietf@nygren.org>>, Mike Bishop <mbishop@evequefou.be<mailto:mbishop@evequefou.be>>


A new version of Internet-Draft
draft-nygren-httpbis-http11-request-binding-00.txt has been successfully
submitted by Erik Nygren and posted to the
IETF repository.

Name:     draft-nygren-httpbis-http11-request-binding
Revision: 00
Title:    HTTP/1.1 Request Smuggling Defense using Cryptographic Message Binding
Date:     2025-10-16
Group:    Individual Submission
Pages:    15
URL:      https://www.ietf.org/archive/id/draft-nygren-httpbis-http11-request-binding-00.txt<https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-nygren-httpbis-http11-request-binding-00.txt__;!!Bt8RZUm9aw!8SW65kTV1j3ovn8oF_js6jwwvkxl31JLh6vH6kmcUorclI41OwJdNsYowFHAiPBvIG1aG2VFgQ$>
Status:   https://datatracker.ietf.org/doc/draft-nygren-httpbis-http11-request-binding/<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/draft-nygren-httpbis-http11-request-binding/__;!!Bt8RZUm9aw!8SW65kTV1j3ovn8oF_js6jwwvkxl31JLh6vH6kmcUorclI41OwJdNsYowFHAiPBvIG3w31jcQg$>
HTML:     https://www.ietf.org/archive/id/draft-nygren-httpbis-http11-request-binding-00.html<https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-nygren-httpbis-http11-request-binding-00.html__;!!Bt8RZUm9aw!8SW65kTV1j3ovn8oF_js6jwwvkxl31JLh6vH6kmcUorclI41OwJdNsYowFHAiPBvIG1hZKWG5g$>
HTMLized: https://datatracker.ietf.org/doc/html/draft-nygren-httpbis-http11-request-binding<https://urldefense.com/v3/__https://datatracker.ietf.org/doc/html/draft-nygren-httpbis-http11-request-binding__;!!Bt8RZUm9aw!8SW65kTV1j3ovn8oF_js6jwwvkxl31JLh6vH6kmcUorclI41OwJdNsYowFHAiPBvIG0_87c3XA$>


Abstract:

   HTTP/1.1 Message Binding adds new hop-by-hop header fields that are
   cryptographically bound to requests and responses.  The keys used are
   negotiated out-of-band from the HTTP datastream (such as via TLS
   Exporters).  These header fields allow endpoints to detect and
   mitigate desynchronization attacks, such as HTTP Request Smuggling,
   that exist due to datastream handling differences.



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