[dns-operations] Google Public DNS plans to enable case randomization for cache poisoning protection

[Tianhao Chi]

As we previously announced, Google Public DNS
<https://developers.google.com/speed/public-dns> is in the process of
enabling case randomization of DNS query names sent to authoritative
nameservers. We have successfully deployed it in some regions in North
America, Europe and Asia protecting the majority (90%) of DNS queries in
those regions not covered by DNS over TLS.

We are still deploying this feature incrementally, location by location.
This is slower than originally planned because of the carefulness and our
estimate of global enabling is around March to April 2023. Meanwhile, we
are monitoring nameserver compliance and actively maintaining an exception
list that disables case randomization for observed non-supporting
nameservers. While our exception list avoids issues with the majority of
the problem servers for now, it may not get immediate updates for newly
broken nameservers in the future. We strongly recommend that nameservers
preserve the query case in the response or support TCP (as we retry over
TCP if case randomization fails) as a fallback.

One subtle issue we’ve seen is that some servers exhibit sporadic
case-randomization non-compliance for the same query parameters. They may
appear to have a short-term response cache that can “replay” answers to
previous or concurrent (differently) case-randomized queries.
If you believe you have discovered name resolution failures with Google
Public DNS due to case randomization, please file a bug in our issue tracker
<https://developers.google.com/speed/public-dns/groups#issue_tracker>. Let
us know if there's any question via
https://developers.google.com/speed/public-dns/groups.

On Thu, Aug 11, 2022 at 4:47 PM Tianhao Chi via dns-operations <
dns-operations at dns-oarc.net> wrote:

>
>
>
> ---------- Forwarded message ----------
> From: Tianhao Chi <chitianhao at google.com>
> To: dns-operations at lists.dns-oarc.net
> Cc:
> Bcc:
> Date: Thu, 11 Aug 2022 16:35:16 -0400
> Subject: Google Public DNS plans to enable case randomization for cache
> poisoning protection
>
> Dear users and nameserver operators,
>
> As part of our efforts to increase DNS cache poisoning protection for UDP
> queries, we are planning to enable case randomization of DNS query names
> sent to most authoritative nameservers (see our *security page
> description*
> <https://developers.google.com/speed/public-dns/docs/security#randomize_case> of
> the feature and
> https://datatracker.ietf.org/doc/html/draft-vixie-dnsext-dns0x20-00). We
> have been performing case randomization of query names since 2009 to a
> small set of chosen nameservers. This set of servers handled a minority of
> our query volume, so a year ago we started work on enabling case
> randomization by default. As part of this, we’ve identified a small set of
> nameservers (< 1000 distinct IPs) that do not handle case randomization
> correctly and have exempted these from case randomization. We are confident
> that case randomization will work without introducing significant increases
> in DNS query volume or resolution failures.
>
> The case-randomized query name in the request will be expected to exactly
> match the name in the question section of the DNS server’s reply, including
> the case of each ASCII letter (A–Z and a–z). For example, if “ExaMplE.CoM”
> is the name sent in the request, the name in the question section of the
> response must also be “ExaMplE.CoM” rather than, e.g., “example.com.”
> Responses that fail to preserve the case of the query name may be dropped
> as potential cache poisoning attacks. Thus, nameservers that fail to
> preserve the query name in their response, or whose response to
> case-randomized requests is an unexpected error (SERVFAIL, NOTIMP, FORMERR,
> etc.) or a failure to respond, will negatively impact users' ability to
> resolve names in the domains they serve.
>
> Generally, when nameservers mishandle case-randomized queries, we
> recommend asking the nameserver operator to correct their behavior. While
> our exception list will work around the problem for now, it may not get
> immediate updates for newly broken name servers.
>
> We’ll have case randomization enabled in one or two regions starting on
> August 29th and enabled globally by the end of October. Meanwhile, we’ve
> already turned off case randomization to nameservers that we’ve identified
> as not handling it correctly.
>
> If you believe you have discovered name resolution failures with Google
> Public DNS due to case randomization, please file a bug in our *issue
> tracker*
> <https://developers.google.com/speed/public-dns/groups#issue_tracker> referencing
> this announcement.
> Let us know if there's any question via
> https://developers.google.com/speed/public-dns/groups. We've also posted
> this in our discussion group:
> https://groups.google.com/g/public-dns-discuss/c/aHSyiIlBfjo.
>
>
>
> ---------- Forwarded message ----------
> From: Tianhao Chi via dns-operations <dns-operations at dns-oarc.net>
> To: dns-operations at lists.dns-oarc.net
> Cc:
> Bcc:
> Date: Thu, 11 Aug 2022 16:35:16 -0400
> Subject: [dns-operations] Google Public DNS plans to enable case
> randomization for cache poisoning protection
> _______________________________________________
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> dns-operations at lists.dns-oarc.net
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>
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