Internet DRAFT - draft-ietf-dnsop-svcb-dane
draft-ietf-dnsop-svcb-dane
dnsop B. M. Schwartz
Internet-Draft Meta Platforms, Inc.
Updates: 6698 (if approved) R. Evans
Intended status: Standards Track Google LLC
Expires: 1 June 2024 29 November 2023
Using DNSSEC Authentication of Named Entities (DANE) with DNS Service
Bindings (SVCB) and QUIC
draft-ietf-dnsop-svcb-dane-03
Abstract
Service Binding (SVCB) records introduce a new form of name
indirection in DNS. They also convey information about the
endpoint's supported protocols, such as whether QUIC transport is
available. This document specifies how DNS-Based Authentication of
Named Entities (DANE) interacts with Service Bindings to secure
connections, including use of port numbers and transport protocols
discovered via SVCB queries. The "_quic" transport name label is
introduced to distinguish TLSA records for DTLS and QUIC.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/bemasc/svcb-dane.
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."
This Internet-Draft will expire on 1 June 2024.
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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/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Using DANE with Service Bindings (SVCB) . . . . . . . . . . . 3
4. Adding a TLSA protocol prefix for QUIC . . . . . . . . . . . 4
5. Operational considerations . . . . . . . . . . . . . . . . . 5
5.1. Recommended configurations . . . . . . . . . . . . . . . 5
5.2. Unintended pinning . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. HTTPS ServiceMode . . . . . . . . . . . . . . . . . . . . 7
7.2. HTTPS AliasMode . . . . . . . . . . . . . . . . . . . . . 7
7.3. QUIC and CNAME . . . . . . . . . . . . . . . . . . . . . 7
7.4. DNS ServiceMode . . . . . . . . . . . . . . . . . . . . . 7
7.5. DNS AliasMode . . . . . . . . . . . . . . . . . . . . . . 8
7.6. New scheme ServiceMode . . . . . . . . . . . . . . . . . 8
7.7. New scheme AliasMode . . . . . . . . . . . . . . . . . . 8
7.8. New protocols . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Unknown Key-Share Attacks . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
The DNS-Based Authentication of Named Entities specification
[RFC7671] explains how clients locate the TLSA record for a service
of interest, starting with knowledge of the service's hostname,
transport, and port number. These are concatenated, forming a name
like _8080._tcp.example.com. It also specifies how clients should
locate the TLSA records when one or more CNAME records are present,
aliasing either the hostname or the initial TLSA query name, and the
resulting server names used in TLS or DTLS.
There are various DNS records other than CNAME that add indirection
to the host resolution process, requiring similar specifications.
Thus, [RFC7672] describes how DANE interacts with MX records, and
[RFC7673] describes its interaction with SRV records.
This document describes the interaction of DANE with indirection via
Service Bindings [SVCB], i.e. SVCB-compatible records such as SVCB
and HTTPS. It also explains how to use DANE with new TLS-based
transports such as QUIC.
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.
The contents of this document apply equally to all SVCB-compatible
record types, such as SVCB and HTTPS records. For brevity, the
abbrevation "SVCB" is used to refer to these record types generally.
3. Using DANE with Service Bindings (SVCB)
Section 6 of [RFC7671] says:
With protocols that support explicit transport redirection via DNS
MX records, SRV records, or other similar records, the TLSA base
domain is based on the redirected transport endpoint rather than
the origin domain.
This document applies the same logic to SVCB-compatible records.
Specifically, if SVCB resolution was entirely secure (including any
AliasMode records and/or CNAMEs), then for each connection attempt
derived from a SVCB-compatible record,
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* The initial TLSA base domain MUST be the final SVCB TargetName
used for this connection attempt. (Names appearing earlier in a
resolution chain are not used.)
* The transport prefix MUST be the transport of this connection
attempt (possibly influenced by the "alpn" SvcParam).
* The port prefix MUST be the port number of this connection attempt
(possibly influenced by the "port" SvcParam).
Resolution security is assessed according to the criteria in
Section 4.1 of [RFC6698].
If the initial TLSA base domain is the start of a secure CNAME chain,
clients MUST first try to use the end of the chain as the TLSA base
domain, with fallback to the initial base domain, as described in
Section 7 of [RFC7671]. However, domain owners SHOULD NOT place a
CNAME record on a SVCB TargetName, as this arrangement is unusual,
inefficient, and at risk for deprecation in a future revision.
If any TLSA QNAME is aliased by a CNAME, clients MUST follow the TLSA
CNAME to complete the resolution of the TLSA records. (This does not
alter the TLSA base domain.)
If a TLSA RRSet is securely resolved, the client MUST set the SNI to
the TLSA base domain of the RRSet. In usage modes other than DANE-
EE(3), the client MUST validate that the certificate covers this base
domain, and MUST NOT require it to cover any other domain.
If the client has SVCB-optional behavior (as defined in Section 3 of
[SVCB]), it MUST use the standard DANE logic described in Section 4.1
of [RFC6698] when falling back to non-SVCB connection.
4. Adding a TLSA protocol prefix for QUIC
Section 3 of [RFC6698] defines the protocol prefix used for
constructing TLSA QNAMEs, and says:
The transport names defined for this protocol are "tcp", "udp",
and "sctp".
When this text was written, there was exactly one TLS-based protocol
defined for each of these transports. However, with the introduction
of QUIC [RFC9000], there are now multiple TLS-derived protocols that
can operate over UDP, even on the same port. To distinguish the
availability and configuration of DTLS and QUIC, this document
updates the above sentence as follows:
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The transport names defined for this protocol are "tcp" (TLS over
TCP [RFC8446]), "udp" (DTLS [RFC9147]), "sctp" (TLS over SCTP
[RFC3436]), and "quic" (QUIC [RFC9000]).
5. Operational considerations
5.1. Recommended configurations
Service consumers are expected to use a CNAME or SVCB AliasMode
record to point at provider-controlled records when possible, e.g.:
alias.example. HTTPS 0 xyz.provider.example.
www.alias.example. CNAME xyz.provider.example.
xyz.provider.example. HTTPS 1 . alpn=h2 ...
xyz.provider.example. A 192.0.2.1
_443._tcp.xyz.provider.example. TLSA ...
If the service needs its own SvcParamKeys, it cannot use CNAME or
AliasMode, so it publishes its own SVCB ServiceMode record with
SvcParams that are compatible with the provider, e.g.:
_dns.dns.example. HTTPS 1 xyz.provider.example. ( alpn=h2 ...
dohpath=/doh{?dns} )
For ease of management, providers may want to alias various TLSA
QNAMEs to a single RRSet:
_443._tcp.xyz.provider.example. CNAME dane-central.provider.example.
dane-central.provider.example. TLSA ...
Any DANE certificate usage mode is compatible with SVCB, but the
usage guidelines from Section 4 of [RFC7671] continue to apply.
5.2. Unintended pinning
As noted in Section 6 of [RFC7671], DANE encounters operational
difficulties when the TLSA RRset is published by an entity other than
the service provider. For example, a customer might copy the TLSA
records into their own zone, rather than publishing an alias to the
TLSA RRset hosted in the service provider's zone. When the service
subsequently rotates its TLS keys, DANE authentication will fail,
resulting in an outage for this customer. Accordingly, zone owners
MUST NOT publish TLSA records for public keys that are not under
their control unless they have an explicit arrangement with the key
holder.
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To prevents the above misconfiguration and ensure that TLS keys can
be rotated freely, service operators MAY reject TLS connections whose
SNI does not correspond to an approved TLSA base domain.
Service Bindings also enable any third party consumer to publish
fixed SvcParams for the service. This can cause an outage or service
degradation if the service makes a backward-incompatible
configuration change. Accordingly, zone owners should avoid
publishing SvcParams for a TargetName that they do not control, and
service operators should exercise caution when making incompatible
configuration changes.
6. Security Considerations
The use of TLSA records specified in this document is independent for
each SVCB connection attempt. In environments where DANE is
optional, this means that the client might use DANE for some
connection attempts but not others when processing a single SVCB
RRSet.
This document only specifies the use of TLSA records when all
relevant DNS records (including SVCB, TLSA, and CNAME records) were
resolved securely. If any of these resolutions were insecure (as
defined in Section 4.3 of [RFC4035]), the client MUST NOT rely on the
TLSA record for connection security. However, if the client would
otherwise have used an insecure plaintext transport, it MAY use an
insecure resolution result to achieve opportunistic security.
Certain protocols that can run over TLS, such as HTTP/1.0, do not
confirm the name of the service after connecting. With DANE, these
protocols are subject to an Unknown Key Share (UKS) attack, in which
the client believes it is connecting to the attacker's domain, but is
actually connecting to an unaffiliated victim domain
[I-D.barnes-dane-uks-00]. Clients SHOULD NOT use DANE with
vulnerable protocols. (HTTP/1.1 and later and encrypted DNS are not
normally vulnerable to UKS attacks, but see Appendix A for some
important exceptions.)
7. Examples
The following examples demonstrate Service Binding interaction with
TLSA base domain selection.
All of the RRSets below are assumed fully-secure with all related
DNSSEC record types omitted for brevity.
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7.1. HTTPS ServiceMode
Given service URI https://api.example.com and record:
api.example.com. HTTPS 1 .
The TLSA QNAME is _443._tcp.api.example.com.
7.2. HTTPS AliasMode
Given service URI https://api.example.com and records:
api.example.com. HTTPS 0 svc4.example.net.
svc4.example.net. HTTPS 0 xyz.cdn.example.
xyz.cdn.example. A 192.0.2.1
The TLSA QNAME is _443._tcp.xyz.cdn.example.
7.3. QUIC and CNAME
Given service URI https://www.example.com and records:
www.example.com. CNAME api.example.com.
api.example.com. HTTPS 1 svc4.example.net alpn=h2,h3 port=8443
svc4.example.net. CNAME xyz.cdn.example.
If the connection attempt is using HTTP/3, the transport label is set
to _quic; otherwise _tcp is used.
The initial TLSA QNAME would be one of:
* _8443._quic.xyz.cdn.example
* _8443._tcp.xyz.cdn.example
If no TLSA record is found, the fallback TLSA QNAME would be one of:
* _8443._quic.svc4.example.net
* _8443._tcp.svc4.example.net
7.4. DNS ServiceMode
Given a DNS server dns.example.com and record:
_dns.dns.example.com. SVCB 1 dns.my-dns-host.example. alpn=dot
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The TLSA QNAME is _853._tcp.dns.my-dns-host.example. The port and
protocol are inferred from the "dot" ALPN value.
7.5. DNS AliasMode
Given a DNS server dns.example.com and records:
_dns.dns.example.com. SVCB 0 dns.my-dns-host.example.
dns.my-dns-host.example. SVCB 1 . alpn=doq
The TLSA QNAME is _853._quic.dns.my-dns-host.example. The port and
protocol are inferred from the "doq" ALPN value.
7.6. New scheme ServiceMode
Given service URI foo://api.example.com:8443 and record:
_8443._foo.api.example.com. SVCB 1 api.example.com.
The TLSA QNAME is _8443._$PROTO.api.example.com, where $PROTO is the
appropriate value for the client-selected transport as discussed in
Section 4 .
7.7. New scheme AliasMode
Given service URI foo://api.example.com:8443 and records:
_8443._foo.api.example.com. SVCB 0 svc4.example.net.
svc4.example.net. SVCB 1 .
svc4.example.net. A 192.0.2.1
The TLSA QNAME is _8443._$PROTO.svc4.example.net (with $PROTO as
above). This is the same if the ServiceMode record is absent.
7.8. New protocols
Given service URI foo://api.example.com:8443 and records:
_8443._foo.api.example.com. SVCB 0 svc4.example.net.
svc4.example.net. SVCB 3 . alpn=foo,bar port=8004
The TLSA QNAME is _8004._$PROTO1.svc4.example.net or
_8004._$PROTO2.svc4.example.net, where $PROTO1 and $PROTO2 are the
transport prefixes appropriate for "foo" and "bar" respectively.
(Note that SVCB requires each ALPN to unambiguously indicate a
transport.)
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8. IANA Considerations
IANA is requested to add the following entry to the "Underscored and
Globally Scoped DNS Node Names" registry ([RFC8552], Section 4):
+=========+============+=================+
| RR Type | _NODE NAME | Reference |
+=========+============+=================+
| TLSA | _quic | (This document) |
+---------+------------+-----------------+
Table 1
9. References
9.1. Normative References
[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>.
[RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
Layer Security over Stream Control Transmission Protocol",
RFC 3436, DOI 10.17487/RFC3436, December 2002,
<https://www.rfc-editor.org/rfc/rfc3436>.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
<https://www.rfc-editor.org/rfc/rfc4035>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/rfc/rfc6698>.
[RFC7671] Dukhovni, V. and W. Hardaker, "The DNS-Based
Authentication of Named Entities (DANE) Protocol: Updates
and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
October 2015, <https://www.rfc-editor.org/rfc/rfc7671>.
[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>.
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[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>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>.
[SVCB] Schwartz, B. M., Bishop, M., and E. Nygren, "Service
Binding and Parameter Specification via the DNS (SVCB and
HTTPS Resource Records)", 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>.
9.2. Informative References
[I-D.barnes-dane-uks-00]
Barnes, R., Thomson, M., and E. Rescorla, "Unknown Key-
Share Attacks on DNS-based Authentications of Named
Entities (DANE)", Work in Progress, Internet-Draft, draft-
barnes-dane-uks-00, 9 October 2016,
<https://datatracker.ietf.org/doc/html/draft-barnes-dane-
uks-00>.
[RFC7672] Dukhovni, V. and W. Hardaker, "SMTP Security via
Opportunistic DNS-Based Authentication of Named Entities
(DANE) Transport Layer Security (TLS)", RFC 7672,
DOI 10.17487/RFC7672, October 2015,
<https://www.rfc-editor.org/rfc/rfc7672>.
[RFC7673] Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA Records
with SRV Records", RFC 7673, DOI 10.17487/RFC7673, October
2015, <https://www.rfc-editor.org/rfc/rfc7673>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>.
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[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017,
<https://www.rfc-editor.org/rfc/rfc8094>.
[RFC8441] McManus, P., "Bootstrapping WebSockets with HTTP/2",
RFC 8441, DOI 10.17487/RFC8441, September 2018,
<https://www.rfc-editor.org/rfc/rfc8441>.
[RFC8552] 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>.
[RFC9103] Toorop, W., Dickinson, S., Sahib, S., Aras, P., and A.
Mankin, "DNS Zone Transfer over TLS", RFC 9103,
DOI 10.17487/RFC9103, August 2021,
<https://www.rfc-editor.org/rfc/rfc9103>.
[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>.
[RFC9250] Huitema, C., Dickinson, S., and A. Mankin, "DNS over
Dedicated QUIC Connections", RFC 9250,
DOI 10.17487/RFC9250, May 2022,
<https://www.rfc-editor.org/rfc/rfc9250>.
Appendix A. Unknown Key-Share Attacks
In the Unknown Key-Share (UKS) Attack [I-D.barnes-dane-uks-00], a
hostile domain ("attacker.example") claims the IP addresses and TLSA
records of another domain ("victim.example"). A client who attempts
to connect to "attacker.example" will actually be connecting to
"victim.example".
The client then sends some commands or requests over this connection.
If the server rejects these requests, or if the attacker could have
forwarded these requests itself, the attack confers no advantage.
However, if the client issues commands that the attacker could not
have issued, and the victim does not ignore these requests, then the
attack could change state at the victim server, reveal confidential
information to the attacker (e.g., via same-origin data sharing in
the client), or waste resources.
Here are some examples of requests that the attacker likely could not
have issued themselves:
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* Requests authenticated using a TLS Client Certificate or other
credential that is bound to the connection but not the domain.
* Requests that are only permitted if they appear to come from a
particular IP range.
This section lists some protocols that can be used with SVCB,
analyzes their vulnerability to this attack, and indicates any
resulting restrictions on their use:
* HTTP/0.9 and HTTP/1.0: *Vulnerable*
- Clients MUST NOT use TLS Client Authentication with DANE and
these protocol versions.
o Example attack: "https://attacker.example/" fetches
"/profile" in Javascript. The second request is directed to
"victim.example" and authenticated by a client certificate,
revealing the user's profile to the attacker.
- Use of these protocol versions with DANE is NOT RECOMMENDED.
* HTTP/1.1 and later: *Slightly Vulnerable*
- The CONNECT method ([RFC9110], Section 3.6) MUST NOT be used on
a connection authenticated with DANE.
o Example attack: "attacker.example" advertises a CONNECT
proxy service to existing customers of the "victim.example"
proxy, which is access-controlled by client IP. To reduce
its own operating costs, "attacker.example" uses UKS to send
users back to "victim.example", resulting in the attacker's
service appearing to work but silently consuming clients'
transfer quota on "victim.example".
- Clients MAY use all other methods with DANE, including Extended
CONNECT [RFC8441]. These methods are defended from
misdirection attacks by server verification of the Host or
:authority header ([RFC9110], Section 7.4).
* DNS over TLS, DTLS, or QUIC [RFC7858][RFC8094][RFC9250]:
- For resolution: *Not Vulnerable*
o DNS resolution does not change state at the server, reveal
confidential information to the attacker, or waste
significant resources.
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- For other uses: *Mitigation Required*
o When using DNS for other purposes such as zone transfers
[RFC9103], clients relying on DANE for server authentication
MUST NOT use a client certificate that is authorized by
multiple potentially hostile servers.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Benjamin M. Schwartz
Meta Platforms, Inc.
Email: ietf@bemasc.net
Robert Evans
Google LLC
Email: evansr@google.com
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