Internet DRAFT - draft-bt-httpbis-reverse-http
draft-bt-httpbis-reverse-http
HTTPBIS B. M. Schwartz
Internet-Draft Meta Platforms, Inc.
Intended status: Standards Track T. Reddy
Expires: 25 April 2024 Nokia
M. Boucadair
Orange
P. S. Tiesel
SAP SE
23 October 2023
Reverse HTTP Transport
draft-bt-httpbis-reverse-http-01
Abstract
This document defines a secure transport for HTTP in which the client
and server roles are reversed. This arrangement improves the origin
server's protection from Layer 3 and Layer 4 denial-of-service
attacks when an intermediary is in use. It allows origin server's to
be hosted without being publicly (and directly) accessible but allows
clients to access these servers via an intermediary.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-bt-httpbis-reverse-http/.
Discussion of this document takes place on the HTTPBIS Working Group
mailing list (mailto:ietf-http-wg@w3.org), which is archived at
http://lists.w3.org/Archives/Public/ietf-http-wg/.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
Schwartz, et al. Expires 25 April 2024 [Page 1]
Internet-Draft Reverse HTTP October 2023
This Internet-Draft will expire on 25 April 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Reverse HTTP: Protocol Overview . . . . . . . . . . . . . . . 4
3.1. Use with Transport Proxies . . . . . . . . . . . . . . . 5
3.2. Discovery of Client-selected Intermediaries . . . . . . . 5
4. Service Binding Mapping . . . . . . . . . . . . . . . . . . . 5
5. Operational Considerations . . . . . . . . . . . . . . . . . 6
5.1. Compatibility . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Efficiency . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Connection Management . . . . . . . . . . . . . . . . . . 6
5.4. Non-public Origins . . . . . . . . . . . . . . . . . . . 7
5.5. Other Applications . . . . . . . . . . . . . . . . . . . 7
6. An Example . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7.1. Stolen Key Attacks . . . . . . . . . . . . . . . . . . . 9
7.2. IP Address Leaks . . . . . . . . . . . . . . . . . . . . 9
7.3. Key Consistency with Oblivious HTTP . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. ALPN IDs . . . . . . . . . . . . . . . . . . . . . . . . 10
8.2. New Scheme . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The Hypertext Transfer Protocol (HTTP) has long supported the ability
of clients to access origins via an intermediary. There are a
variety of well-defined intermediary types:
Schwartz, et al. Expires 25 April 2024 [Page 2]
Internet-Draft Reverse HTTP October 2023
* Client-selected
- HTTP request proxies (a.k.a. forward proxies)
- Transport proxies (e.g., CONNECT (Section 9.3.6 of [RFC9110]),
CONNECT-UDP [RFC9298])
- IP relays (e.g., CONNECT-IP [I-D.ietf-masque-connect-ip])
- Oblivious HTTP Relays [I-D.ietf-ohai-ohttp]
* Origin-selected
- HTTP gateways (a.k.a. reverse proxies)
- Transport load balancers (e.g., Performance-Enhancing Proxies
(PEPs, Section 2.1.1 of [RFC3135])
Although these intermediaries differ widely in their functionality,
many of them act as an HTTP client when connecting to the origin.
Client-selected intermediaries reach the origin based on its hostname
or IP address specified in the HTTP request, while origin-selected
intermediaries first translate this destination address into a
"backend address".
One of the main advantages of origin-selected intermediaries is their
ability to defend the origin from attacks, especially Denial of
Service (DoS) and Distributed Denial-of-Service (DDoS) attacks in
which an attacker floods the origin server with requests/packets. To
prevent attackers from simply bypassing the intermediary, common
practices include keeping the backend address hidden and/or
instituting filtering rules (ACL, typically) that only allow packets
from the intermediary. These practices are reasonably effective with
origin-selected intermediaries, but they cannot be used with client-
selected intermediaries, as those intermediaries do not know the
hidden backend IP address and/or port number, and the origin does not
know their "exit" IP addresses.
This specification defines a protocol for HTTP connections between
origins and arbitrary intermediaries that can limit the impact of
Layer 3 and Layer 4 DoS/DDoS attacks. When this protocol is in use,
origins have the ability to partition the infrastructure that serves
each intermediary. This ensures that attacks targeting the origin's
public IP address or attacks via one intermediary will not affect any
other intermediaries. By partitioning the infrastructure, the impact
of the attacks is contained within the affected intermediary or the
origin's public IP address.
Schwartz, et al. Expires 25 April 2024 [Page 3]
Internet-Draft Reverse HTTP October 2023
This protocol works by reversing the roles of the Transport Layer
Security (TLS) or QUIC transport that supports an HTTP connection:
the origin acts as the transport client, and the intermediary acts as
the server. HTTP operates normally inside the secure transport but
with the client and server roles reversed.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Reverse HTTP: Protocol Overview
The protocol defined in this document is termed "Reverse HTTP". The
"Reverse HTTP/2" version is identified by the ALPN ID "h2-reverse",
and "Reverse HTTP/3" by "h3-reverse" (see Section 8.1). These
protocols represent HTTP/2 and HTTP/3, operating with the roles
reversed but otherwise unmodified, except as follows:
* The intermediary MUST send a TLS CertificateRequest message
(Section 4.4.2 of [RFC8446]) to indicate that certificate-based
client authentication is required.
* The origin MUST respond with a valid certificate chain.
* Each party MUST send a SETTINGS frame (Section 6.5 of [RFC9113])
as soon as the transport becomes writable to them. This means
that the intermediary will typically send its SETTINGS frame
first.
* The origin MUST immediately send an ORIGIN frame identifying the
origins it claims. This frame is used as originally defined,
except that wildcard names are permitted (contrary to Section 2.2
of [RFC8336]).
- Otherwise, use of Reverse HTTP with wildcard certificates would
be impossible.
* The intermediary MUST check the ORIGIN frame contents against the
provided TLS client certificate.
Reverse HTTP/1.1 is not defined, as the lack of multiplexing renders
it unsuitable for this use.
Schwartz, et al. Expires 25 April 2024 [Page 4]
Internet-Draft Reverse HTTP October 2023
Once this process has completed, the origin has proved ownership of
the Origin Set and is ready to receive requests. The intermediary
SHOULD direct subsequent HTTP requests for this origin over this
Reverse HTTP channel absent explicit policy (e.g., overload limit or
ACL). For example, a policy can be provided to the intermediary to
help determining unacceptable load threshold.
3.1. Use with Transport Proxies
Transport proxies do not normally act as HTTP clients, so they cannot
use Reverse HTTP directly. Instead, if a transport proxy receives a
request whose destination host and port number appears in the Origin
Set, the proxy establishes a transport proxy connection to this
origin over the Reverse HTTP connection. For example, this
corresponds to an HTTP CONNECT request for TCP, and for UDP it
corresponds to an extended-CONNECT request with the "connect-udp"
protocol, using the registered .well-known URI template.
Note that transport destinations identified by an IP address can only
use this mechanism if the origin's certificate includes that IP
address explicitly.
For IP relays, the destination does not include a port number. By
default, the intermediary MUST add a port number of 443 before
attempting to forward packets using this procedure.
3.2. Discovery of Client-selected Intermediaries
The HTTP "Via" header can indicate the presence of a client-selected
intermediary. If a "Via" header arrives with an unrecognized host,
the origin MAY attempt a Reverse HTTP connection for use by future
requests from this intermediary. If the intermediary does not
confirm the protocol via ALPN, the origin MUST close the connection.
4. Service Binding Mapping
Intermediaries that support Reverse HTTP SHOULD indicate this by
publishing a SVCB record [I-D.ietf-dnsop-svcb-https] with port-prefix
naming, using the scheme "http-reverse" with a default port number of
443. Applicable SvcParamKeys include "alpn", "ipv4hint"/"ipv6hint",
and "port". There is no default ALPN value, so the "alpn" key is
REQUIRED.
proxy.example.net. IN HTTPS 1 . alpn=h2,h3 ech=ABC..123
_http-reverse.proxy.example.net. IN SVCB 1 proxy.example.net. \
alpn=h2-reverse,h3-reverse ech=ABC..123
Schwartz, et al. Expires 25 April 2024 [Page 5]
Internet-Draft Reverse HTTP October 2023
Figure 1: Example Records for a Forward Proxy that Supports
Reverse HTTP
5. Operational Considerations
5.1. Compatibility
Reverse HTTP applies to a single hop of a multihop HTTP connection,
especially the hop between an intermediary and the origin. When used
in this way, Reverse HTTP is compatible with any ordinary HTTP user
agent, and user agents ordinarily cannot tell that Reverse HTTP is in
use. (Reverse HTTP does not alter the contents of the "Via" response
header.)
5.2. Efficiency
Reverse HTTP does not use appreciably more bandwidth or CPU time than
ordinary HTTP on active connections. However, it is much less
efficient for idle connections, which use memory and other
connection-related resources on the intermediary even when no
requests are being processed.
5.3. Connection Management
To accommodate loss of state in firewalls or translators (Section 2
of [RFC6269]), especially in the absence of application traffic, the
origin SHOULD use appropriate transport-level keepalives and MUST re-
establish a new connection when an application-level communication
has failed.
Origins backed by multiple servers MAY attempt to establish a
separate Reverse HTTP connection from each one in order to tolerate
node failures and support optimized path selection. However,
intermediaries SHOULD limit the number of idle Reverse HTTP
connections operated on behalf of each registrable domain, in order
to avoid resource exhaustion attacks. A local configuration may be
provided to an intermediary to control the maximum number of active
connections.
For very high-traffic origins and multi-instance intermediaries, a
disruption could occur if the intermediary immediately directs all
user traffic onto the first Reverse HTTP connection. Very large
intermediaries SHOULD ensure that transitions to Reverse HTTP are
gradual, so that large origins have time to establish multiple
connections.
Note: define more what is meant precisly by "Very large", "multi-
instance", etc.
Schwartz, et al. Expires 25 April 2024 [Page 6]
Internet-Draft Reverse HTTP October 2023
5.4. Non-public Origins
In some cases, an HTTP origin may be intended exclusively for use via
one or more client-selected intermediaries that are known to the
origin. In this situation, the publication of DNS records outside a
domain for the origin is OPTIONAL.
5.5. Other Applications
Reverse HTTP is principally intended for use between intermediaries
and origins. It is not applicable to general HTTP clients, as it
requires that the origin knows that the client will issue a request
before the request occurs. However, in cases where an HTTP client is
publicly reachable and produces frequent requests to one origin over
a long period of time, Reverse HTTP may be applicable. It is out of
scope of this document to identify a comprehensive list of the
protocol applicability.
6. An Example
The following shows the example of the reverse HTTP in the context of
Oblivious HTTP deployments.
Schwartz, et al. Expires 25 April 2024 [Page 7]
Internet-Draft Reverse HTTP October 2023
.------------------------------.
+---------+ +----------+ | +----------+ +----------+ |
| Client | | Relay | | | Gateway | | Target | |
| | | Resource | | | Resource | | Resource | |
+----+----+ +----+-----+ | +-----+----+ +----+-----+ |
| | `-------|--------------|-------'
| | Initiate TCP | |
| | handshake | |
| |<-------------------+ |
| | Initiate TLS with | |
| | ALPN="h2-reverse" | |
| |<-------------------+ |
| | CertificateRequest,| |
| | HTTP SETTINGS | |
| +------------------->| |
| | CertificateVerify, | |
| | SETTINGS, ORIGIN | |
| |<-------------------+ |
| .-------------. | | |
| | Validate | | | |
| | certificate & |+-+| | |
| | role reversal | | | |
| `-------------' | | |
| | | |
| Relay | | |
| Request | | |
| [+ Encapsulated | | |
| Request ] | | |
+-------------------->| Gateway | |
| | Request | |
| | [+ Encapsulated | |
| | Request ] | |
| +------------------->| Request |
| | +------------->|
| | | |
| | | Response |
| | Gateway |<-------------+
| | Response | |
| | [+ Encapsulated | |
| | Response ] | |
| Relay |<-------------------+ |
| Response | | |
| [+ Encapsulated | | |
| Response ] | | |
|<--------------------+ | |
| | | |
Figure 2: Example: Reverse HTTP/2 for Oblivious HTTP
Schwartz, et al. Expires 25 April 2024 [Page 8]
Internet-Draft Reverse HTTP October 2023
7. Security Considerations
7.1. Stolen Key Attacks
As noted in Section 4 of [RFC8336], accepting ORIGIN frames without
DNS confirmation facilitates the use of stolen keys, and thus
increases the incentive to steal these keys. The mitigations listed
in that section also apply here, and are RECOMMENDED. Intermediaries
also MAY impose a DNS confirmation requirement, although this weakens
the DoS/DDoS defense provided by Reverse HTTP (Section 7.2).
QUESTION: Should we do more about this? For example, we could
define an OID to mark these certificates as Reverse HTTP-only, or
we could commit to an IP range by placing a MAC in a DNS record
and revealing the message via a SETTINGS value.
7.2. IP Address Leaks
One goal of Reverse HTTP is to prevent DoS/DDoS attackers from
learning the IP addresses used by an origin to communicate with this
intermediary. These IP addresses can be leaked in various ways,
requiring certain mitigations:
* In the ordinary DNS address records for the origin.
- Origins SHOULD use different IP addresses for Reverse HTTP
(unless the intermediary imposes a DNS confirmation requirement
as described in Section 7.1).
* In the Proxy-Status HTTP header field's "next-hop" attribute.
- Intermediaries MUST NOT populate the "next-hop" attribute when
using Reverse HTTP to the origin.
* From the probes sent to intermediaries discovered from the "Via"
header field.
- Origins SHOULD use distinct, unrelated IP addresses to contact
each intermediary.
* From connection monitoring of the ALPN values in ClientHellos.
- Intermediaries MAY use a single Encrypted ClientHello
configuration for HTTP and Reverse HTTP.
* From statistical analysis of traffic patterns.
- Origins SHOULD regularly change the IP address that is used.
Schwartz, et al. Expires 25 April 2024 [Page 9]
Internet-Draft Reverse HTTP October 2023
Even if the origin's Reverse HTTP IP addresses do leak, Reverse HTTP
still provides significant protection by simplifying the filtering
rules required to block unsolicited connections.
7.3. Key Consistency with Oblivious HTTP
The security considerations for the Oblivious HTTP (Section 8 of
[OHTTP]) as well as the security considerations for Discovery of
Oblivious Services via Service Binding Records (Section 6 of
[OHAI-SVCB]) apply.
[CONSISTENCY] provides an analysis of the options for ensuring the
key configurations are consistent between different clients. Clients
MUST employ techniques to mitigate key targeting attacks. Note that
the option of confirming the key with a shared proxy as described in
[CONSISTENCY] will work if the Oblivious HTTP relay and the forward
proxy operate from a single origin.
8. IANA Considerations
8.1. ALPN IDs
This document rquests IANA to add two new registrations in the "TLS
Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry
[RFC7301]:
+==========+====================================+===============+
| Protocol | Identification Sequence | Specification |
+==========+====================================+===============+
| Reverse | 0x68 0x32 0x2d 0x72 0x65 0x76 0x65 | (This |
| HTTP/2 | 0x72 0x73 0x65 ("h2-reverse") | document) |
+----------+------------------------------------+---------------+
| Reverse | 0x68 0x33 0x2d 0x72 0x65 0x76 0x65 | (This |
| HTTP/3 | 0x72 0x73 0x65 ("h3-reverse") | document) |
+----------+------------------------------------+---------------+
Table 1
8.2. New Scheme
Per [Attrleaf], IANA is requested to add the following entry to the
DNS Underscore Global Scoped Entry registry:
Schwartz, et al. Expires 25 April 2024 [Page 10]
Internet-Draft Reverse HTTP October 2023
+=========+===============+============================+
| RR TYPE | _NODE NAME | Reference |
+=========+===============+============================+
| SVCB | _http-reverse | (This document, Section 4) |
+---------+---------------+----------------------------+
Table 2
TODO: Register the URI scheme as well.
9. References
9.1. Normative References
[I-D.ietf-dnsop-svcb-https]
Schwartz, B. M., Bishop, M., and E. Nygren, "Service
binding and parameter specification via the DNS (DNS SVCB
and HTTPS RRs)", Work in Progress, Internet-Draft, draft-
ietf-dnsop-svcb-https-12, 11 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-
svcb-https-12>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8336] Nottingham, M. and E. Nygren, "The ORIGIN HTTP/2 Frame",
RFC 8336, DOI 10.17487/RFC8336, March 2018,
<https://www.rfc-editor.org/rfc/rfc8336>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
Schwartz, et al. Expires 25 April 2024 [Page 11]
Internet-Draft Reverse HTTP October 2023
9.2. Informative References
[Attrleaf] Crocker, D., "Scoped Interpretation of DNS Resource
Records through "Underscored" Naming of Attribute Leaves",
BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019,
<https://www.rfc-editor.org/rfc/rfc8552>.
[CONSISTENCY]
Davidson, A., Finkel, M., Thomson, M., and C. A. Wood,
"Key Consistency and Discovery", Work in Progress,
Internet-Draft, draft-ietf-privacypass-key-consistency-01,
10 July 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-privacypass-key-consistency-01>.
[I-D.ietf-masque-connect-ip]
Pauly, T., Schinazi, D., Chernyakhovsky, A., Kühlewind,
M., and M. Westerlund, "Proxying IP in HTTP", Work in
Progress, Internet-Draft, draft-ietf-masque-connect-ip-13,
28 April 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-masque-connect-ip-13>.
[I-D.ietf-ohai-ohttp]
Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in
Progress, Internet-Draft, draft-ietf-ohai-ohttp-10, 25
August 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-ohai-ohttp-10>.
[OHAI-SVCB]
Pauly, T. and T. Reddy.K, "Discovery of Oblivious Services
via Service Binding Records", Work in Progress, Internet-
Draft, draft-ietf-ohai-svcb-config-07, 6 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ohai-
svcb-config-07>.
[OHTTP] Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in
Progress, Internet-Draft, draft-ietf-ohai-ohttp-10, 25
August 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-ohai-ohttp-10>.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/rfc/rfc3135>.
Schwartz, et al. Expires 25 April 2024 [Page 12]
Internet-Draft Reverse HTTP October 2023
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<https://www.rfc-editor.org/rfc/rfc6269>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9298] Schinazi, D., "Proxying UDP in HTTP", RFC 9298,
DOI 10.17487/RFC9298, August 2022,
<https://www.rfc-editor.org/rfc/rfc9298>.
Authors' Addresses
Benjamin M. Schwartz
Meta Platforms, Inc.
Email: ietf@bemasc.net
Tirumaleswar Reddy
Nokia
Email: kondtir@gmail.com
Mohamed Boucadair
Orange
Email: mohamed.boucadair@orange.com
Philipp S. Tiesel
SAP SE
Email: philipp@tiesel.net
Schwartz, et al. Expires 25 April 2024 [Page 13]
