| Internet-Draft | Glueless DNS | September 2021 |
| Dickson | Expires 20 March 2022 | [Page] |
This Internet Draft proposes a Best Current Practice for protecting authority servers against MITM and poisoning attacks, using a domain naming strategy to not require glue A/AAAA records and use of DNSSEC.¶
This BCP assumes the use of validating resolvers, which should already be a BCP itself.¶
MITM and poisoning attacks should only be effective/possible against unsigned domains.¶
However, until all domains are signed, this guidance is relevant, in that it can limit the attack surface of unsigned domains.¶
This guidance should be combined with [I-D.dickson-dnsop-ds-hack]¶
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/.¶
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This Internet-Draft will expire on 20 March 2022.¶
Copyright (c) 2021 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.¶
DNS Security extensions (DNSSEC) are additions to the DNS protocol which provide data integrity and authenticity protections, but do not provide privacy.¶
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.¶
Use of DNSSEC requires upgrades to software for authorative servers, resolvers, and optionally clients, in order to benefit from these protections. It also requires that DNS operators actually sign their zones.¶
When a given zone is unsigned, those protections to the zone contents are not available.¶
Any unsigned zone is trivially able to be altered by an on-path attacker.¶
An off-path attacker is limited to use of cache poisoning attacks.¶
However, some class of cache poisoning attacks target unsigned delegation data. These records consist of the necessary NS records, and when necessary, "glue" records for IP address corresponding to these NS records.¶
The impact to successful cache poisoning of delegation records is that the attacker may substitute their own name servers for the legitimate name server. In other words, the attacker is able to promote itself to being effectively on-path, and trivially modify unsigned domain results.¶
There are two delegation record types that require protection against off-path attackers, for unsigned domains.¶
For protecting NS records used in delegations, there is a new proposal for use of a new DS record. See [I-D.dickson-dnsop-ds-hack] for details.¶
The present draft addresses the "glue" records, by recommending methods to make them unnecessary. If there is no delegation glue data, an attacker cannot poison that data. The resolver cache would contain only authoritative data, which cannot be pre-empted by such poisoning attacks.¶
The following practice is RECOMMENDED for unsigned zones:¶
Example:¶
Do NOT do the following (delegations requiring glue): unsigned-zone.example NS ns1.unsigned-zone.example unsigned-zone.example NS ns2.unsigned-zone.example // glue ns1.unsigned-zone.example A (IP address) ns1.unsigned-zone.example AAAA (IP address) ns2.unsigned-zone.example A (IP address) ns2.unsigned-zone.example AAAA (IP address) Instead, do the following (glueless delegations): unsigned-zone.example NS ns1.nameserver-signed-zone.example unsigned-zone.example NS ns2.nameserver-signed-zone.example // // Delegation to signed zone containing name server names nameserver-signed-zone.example NS ns1.nameserver-signed-zone.example nameserver-signed-zone.example NS ns2.nameserver-signed-zone.example nameserver-signed-zone.example DS (DS record data) // glue records for this delegation ns1.nameserver-signed-zone.example A (IP address) ns1.nameserver-signed-zone.example A (IP address) ns2.nameserver-signed-zone.example AAAA (IP address) ns2.nameserver-signed-zone.example AAAA (IP address)¶
The following practice is RECOMMENDED (for signed name server name zones, i.e. large operators' zones):¶
Example:¶
Entries in the example TLD // // Same unsigned zone uses the same name servers // However, the name server is in its own glueless zone unsigned-zone.example NS ns1.nameserver-signed-zone.example unsigned-zone.example NS ns2.nameserver-signed-zone.example // nameserver-signed-zone.example NS ns1.separate-zone.example nameserver-signed-zone.example NS ns2.separate-zone.example nameserver-signed-zone.example DS (DS record data) // separate-zone.example NS special-ns1.separate-zone.example separate-zone.example NS special-ns2.separate-zone.example separate-zone.example DS (DS record data) // glue for special-ns1 and -2 // special-ns1 and -2 are used only for/by separate-zone special-ns1.separate-zone.example A (IP address) special-ns1.separate-zone.example AAAA (IP address) special-ns2.separate-zone.example A (IP address) special-ns2.separate-zone.example AAAA (IP address) Zone file for nameserver-signed-zone: nameserver-signed-zone.example SOA (soa record data) // glueless NS are used nameserver-signed-zone.example NS ns1.separate-zone.example nameserver-signed-zone.example NS ns2.separate-zone.example // actual glueless address records for "real" name server names ns1.nameserver-signed-zone.example A (IP address) ns1.nameserver-signed-zone.example AAAA (IP address) ns2.nameserver-signed-zone.example A (IP address) ns2.nameserver-signed-zone.example AAAA (IP address) // etc etc etc Zone file for separate-zone: separate-zone.example SOA (soa record data) // This is the only non-glueless NS in use // NB: matches glue in parent separate-zone.example NS special-ns1.separate-zone.example separate-zone.example NS special-ns2.separate-zone.example special-ns1.separate-zone.example A (IP address) special-ns1.separate-zone.example AAAA (IP address) special-ns2.separate-zone.example A (IP address) special-ns2.separate-zone.example AAAA (IP address) // actual address records for "real" name server name // (only used by nameserver-signed-zone) ns1.separate-zone.example A (IP address) ns1.separate-zone.example AAAA (IP address) ns2.separate-zone.example A (IP address) ns2.separate-zone.example AAAA (IP address)¶
This guidance is not a substitute for use of DNSSEC for DNS domains.¶
This guidance is useful in preventing off-path attackers from poisoning DNS cache entries necessary for delegations.¶
However, an on-path attacker is still able to manipulate DNS responses sent over UDP or unencrypted TCP.¶
Use of an encrypted transport is one potential method of preventing MITM attacks (i.e. DNS over TLS from resolver to authoritative server, aka ADoT), but this is still less secure than use of DNSSEC.¶
This document has no IANA actions.¶
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