



DNS Operations (dnsop)                                          Y.Q. Qiu
Internet-Draft                                                   X.L. Li
Intended status: Standards Track                       Nankai University
Expires: 20 January 2026                                       July 2025


    Enhanced Bailiwick Checking for DNS Resolvers to Mitigate Cache
                       Poisoning Vulnerabilities
                 draft-qiu-dnsop-enhanced-bailiwick-00

Abstract

   The Domain Name System (DNS) relies on caching to function
   efficiently.  However, DNS cache poisoning remains a significant
   threat.  The "bailiwick" rule is a fundamental security mechanism
   intended to prevent resolvers from caching out-of-bailiwick data sent
   by malicious or misconfigured authoritative servers.  Current DNS
   standards provide high-level guidance on bailiwick checking but lack
   specific algorithmic definitions, leading to inconsistent
   implementations across different DNS software.  These inconsistencies
   can be exploited, particularly in DNS servers that operate in
   multiple modes, such as Conditional DNS Servers (CDNS), which may act
   as both recursive resolvers and forwarders and often share a common
   cache.

   This document specifies enhanced and more precise rules for bailiwick
   checking in DNS resolvers, including those operating as forwarders or
   CDNS.  The goal is to provide clearer guidelines for implementers,
   reduce the attack surface for cache poisoning, and improve the
   overall security and robustness of the DNS infrastructure.  The
   recommendations herein are informed by recent research highlighting
   vulnerabilities in existing bailiwick implementations.

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."




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   This Internet-Draft will expire on 2 January 2026.

Copyright Notice

   Copyright (c) 2025 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
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   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
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.3.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Background: Bailiwick Checking and its Challenges . . . . . .   5
     2.1.  Current Understanding of Bailiwick  . . . . . . . . . . .   5
     2.2.  Observed Implementation Inconsistencies . . . . . . . . .   5
     2.3.  Conditional DNS Servers (CDNS)  . . . . . . . . . . . . .   6
   3.  Normative Requirements for Bailiwick Checking . . . . . . . .   6
     3.1.  General Principles  . . . . . . . . . . . . . . . . . . .   6
     3.2.  Determining the Query Zone (Q.ZONE) . . . . . . . . . . .   7
       3.2.1.  Recursive Resolution Mode . . . . . . . . . . . . . .   7
       3.2.2.  Forwarding Mode . . . . . . . . . . . . . . . . . . .   7
     3.3.  Sanitizing Records in a Response  . . . . . . . . . . . .   8
       3.3.1.  Answer Section  . . . . . . . . . . . . . . . . . . .   8
       3.3.2.  Authority Section . . . . . . . . . . . . . . . . . .   8
       3.3.3.  Additional Section  . . . . . . . . . . . . . . . . .   9
     3.4.  CNAME Chasing . . . . . . . . . . . . . . . . . . . . . .  10
   4.  Bailiwick Checking in Conditional DNS Servers (CDNS)  . . . .  11
     4.1.  Cache Interaction and Integrity . . . . . . . . . . . . .  11
     4.2.  Forwarding Fallback Considerations  . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction




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1.1.  Motivation

   Bailiwick checking is a critical defense mechanism in the DNS
   designed to ensure that a DNS server only accepts and caches data for
   which the responding server is authoritative.  As defined in
   [RFC1034] and [RFC1035], authoritative nameservers should not return
   data for zones they do not manage.  Resolvers are expected to enforce
   this by discarding "unsolicited" or out-of-bailiwick data.

   However, the precise algorithms for bailiwick checking are not
   rigorously defined in existing standards, leading to diverse
   interpretations and implementations by DNS software vendors.  Recent
   research, such as "The Maginot Line: Attacking the Boundary of DNS
   Caching Protection" [MAGINOTDNS], has exposed vulnerabilities
   stemming from these inconsistencies.  These vulnerabilities can allow
   attackers to inject malicious records into a resolver's cache,
   potentially hijacking entire DNS zones, including Top-Level Domains
   (TLDs).

   Conditional DNS Servers (CDNS), which combine recursive resolver and
   forwarder functionalities and often share a global cache, present a
   particular challenge.  Weaknesses in the bailiwick checks of one mode
   (e.g., forwarding) can be exploited to poison the cache used by
   another, more secure mode (e.g., recursive resolution).

   This document aims to address these issues by providing more explicit
   and robust rules for bailiwick checking.  The goal is to foster more
   consistent and secure implementations across DNS resolver software,
   thereby strengthening the overall resilience of the DNS ecosystem
   against cache poisoning attacks.

1.2.  Requirements Language

   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.

1.3.  Terminology

   This document uses standard DNS terminology as defined in [RFC1034],
   [RFC1035], and [RFC8499].  The following terms are central to this
   document:

   Bailiwick:





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      The scope of authority a nameserver has.  Data is considered "in-
      bailiwick" if it pertains to the zone(s) for which the responding
      nameserver is authoritative in the context of the original query.

   Out-of-Bailiwick:
      Data that is not within the bailiwick of the responding
      nameserver.

   Q.NAME:
      The domain name in the question section of the current query being
      processed by the resolver.

   Q.TYPE:
      The type of the resource record (RR) in the question section of
      the current query.

   Q.ZONE:
      The closest ancestor zone for which the resolver has (or believes
      it has) authoritative nameserver information relevant to Q.NAME.
      This zone defines the current bailiwick against which incoming
      response records are checked.  The determination of Q.ZONE is
      critical and is further detailed in Section 3.2.

   RR (Resource Record):
      A single record in a DNS response.  RR.NAME is the owner name of
      the resource record.  RR.TYPE is the type of the resource record.
      RR.DATA is the data content of the resource record.

   CDNS (Conditional DNS Server):
      A DNS server configured to act as both a recursive resolver and a
      forwarder simultaneously, often directing queries to different
      upstream servers or resolving them differently based on the
      queried domain name.  CDNS implementations typically use distinct
      sets of zones:

      $Z_R$ (Recursive DNS Zones): The set of domain names for which the
      CDNS is configured to perform recursive resolution.

      $Z_F$ (Forwarding DNS Zones): The set of domain names for which
      the CDNS is configured to forward queries to specific upstream
      forwarders.

   Delegation:
      The process by which a nameserver for a parent zone indicates the
      authoritative nameservers for a child zone, typically via NS
      records.

   Referral:



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      A DNS response from a nameserver that does not have the
      authoritative answer for a query but provides NS records (and
      potentially glue records) pointing to nameservers that are
      authoritative for a zone closer to the Q.NAME.

   Sanitize Records:
      The process of examining each RR in a DNS response to determine if
      it is in-bailiwick and should be processed and potentially cached.

2.  Background: Bailiwick Checking and its Challenges

2.1.  Current Understanding of Bailiwick

   The concept of bailiwick is fundamental to DNS security.  [RFC1034]
   states that nameservers should not add RRs to the additional section
   unless they are "closely related to an RR in the answer or authority
   sections".  More generally, data returned by a nameserver should be
   within the scope of the zones for which it holds authority, relative
   to the query that was made.  Resolvers are expected to discard data
   that violates this principle [RFC2181].

   The primary goal of bailiwick checking is to prevent a malicious
   nameserver authoritative for example.com from providing (and a
   resolver from caching) records for other-example.net, or worse, for
   TLDs or the root zone.

2.2.  Observed Implementation Inconsistencies

   Despite the long-standing principle of bailiwick, its implementation
   varies.  The [MAGINOTDNS] study highlights several critical areas of
   inconsistency and vulnerability:

   1.  Q.ZONE Initialization: In forwarding mode, some DNS software
       initializes Q.ZONE to overly broad zones (e.g., the root zone
       ".") or an ancestor of Q.NAME that is too high in the DNS
       hierarchy.  This effectively weakens or nullifies bailiwick
       checks for records in the authority and additional sections, as
       almost any record would appear to be "in-bailiwick" relative to
       the root.  This is referred to as V1 in [MAGINOTDNS].

   2.  CNAME Chasing Logic: Flaws in how bailiwick context is maintained
       or re-evaluated during CNAME chasing can lead to vulnerabilities
       where a resolver is tricked into accepting out-of- bailiwick data
       for the CNAME target.  This is referred to as V2 in [MAGINOTDNS].







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   3.  Shared Cache in CDNS: When recursive and forwarding modes in a
       CDNS share a global cache, data cached via the potentially weaker
       bailiwick checks of the forwarding mode can pollute the cache for
       the recursive mode.

   These inconsistencies underscore the need for more precise normative
   guidance.

2.3.  Conditional DNS Servers (CDNS)

   CDNS are increasingly common in enterprise networks and ISP
   infrastructure.  They offer flexible query routing, allowing
   organizations to resolve internal domains locally while forwarding
   external domains to public resolvers, or to implement split-horizon
   DNS, content delivery optimizations, or security policies.

   The dual nature of CDNS, coupled with shared caching, makes them a
   prime target if bailiwick checks are inconsistent between modes.  An
   attacker might exploit a vulnerability in the forwarding path's
   bailiwick logic to inject malicious data that subsequently affects
   recursive resolution for other clients or other domains.

3.  Normative Requirements for Bailiwick Checking

3.1.  General Principles

   The following general principles MUST be applied by DNS resolvers
   when processing responses and considering records for caching:

   GP1:
      A resolver MUST NOT cache any RR from a response if that RR is
      determined to be out-of-bailiwick according to the rules specified
      in this document.

   GP2:
      The bailiwick checks applied to data received in forwarding mode
      MUST be at least as stringent as those applied in recursive
      resolution mode if the forwarded data can be stored in a cache
      that is also accessible by the recursive resolution process.

   GP3:
      The Q.ZONE for a query is established at the time the query is
      sent and is used to validate the response.  It represents the zone
      for which the queried upstream server is considered authoritative
      in the context of the current Q.NAME.






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3.2.  Determining the Query Zone (Q.ZONE)

   The correct determination of Q.ZONE is paramount for effective
   bailiwick checking.

3.2.1.  Recursive Resolution Mode

   When a resolver is performing recursive resolution and is about to
   send a query for Q.NAME to a set of selected authoritative
   nameservers:

   RRM1:
      Q.ZONE MUST be set to the name of the zone for which the selected
      upstream nameservers are authoritative.  This is typically the
      closest ancestor of Q.NAME (or Q.NAME itself) for which the
      resolver has NS records in its cache, or the root zone (".") if no
      closer NS records are available.

3.2.2.  Forwarding Mode

   When a resolver is configured to forward queries for domains within a
   specific forwarding zone ($Z_F$) to a designated set of upstream
   forwarders:

   FM1:
      If the Q.NAME falls within a configured forwarding zone $Z_F$
      (e.g., Q.NAME is host.internal.example.com and $Z_F$ is
      internal.example.com), then Q.ZONE for the query sent to the
      upstream forwarder SHOULD be set to that $Z_F$
      (internal.example.com).

   FM2:
      If the resolver is acting as a general-purpose forwarder (e.g.,
      forwarding all queries for which it is not authoritative itself)
      and is configured to forward to a specific recursive resolver
      (e.g., a public DNS service), Q.ZONE SHOULD be considered the root
      zone (".").  However, if this forwarder caches responses and that
      cache is shared with a recursive resolution component (as in a
      CDNS), this broad Q.ZONE definition is insufficient.  See
      Section 4 for CDNS-specific rules.

   FM3:









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      A resolver in forwarding mode, especially if part of a CDNS that
      shares its cache with a recursive component, MUST NOT initialize
      Q.ZONE to the root zone (".") or an overly broad ancestor if a
      more specific zone context (like a configured $Z_F$) is available
      for Q.NAME.  Relying on an upstream recursive resolver to perform
      all bailiwick checks is NOT SUFFICIENT if the forwarding resolver
      itself caches the results in a shared cache.

   FM4:
      If a forwarder forwards to an authoritative server directly (not a
      recursive resolver), Q.ZONE MUST be the zone for which that
      authoritative server is believed to be authoritative for Q.NAME.

3.3.  Sanitizing Records in a Response

   Upon receiving a response (R) to a query (Q), each RR in the answer,
   authority, and additional sections of R MUST be checked against
   Q.ZONE.

3.3.1.  Answer Section

   AS1:
      For an RR in the answer section to be considered in-bailiwick:

      a.  RR.NAME MUST be equal to Q.NAME (or an alias of Q.NAME if
      CNAMEs/DNAMEs are involved, see Section 3.4).

      b.  RR.TYPE MUST be equal to Q.TYPE (unless Q.TYPE is ANY or
      CNAME/DNAME processing is occurring).

      c.  If RR.TYPE is CNAME or DNAME, specific CNAME/DNAME processing
      rules apply (see Section 3.4 and [RFC6672]).

   AS2:
      Records in the answer section that do not meet these criteria MUST
      be discarded and NOT cached, unless they are part of a valid
      CNAME/DNAME chain leading to the Q.NAME.

3.3.2.  Authority Section

   The authority section typically contains NS records for delegations
   or SOA records for negative answers.

   AuthS1:
      For an NS record in the authority section (RR.TYPE is NS) to be
      considered in-bailiwick:





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      a.  RR.NAME (the zone being delegated) MUST be a sub-domain of
      Q.ZONE, or Q.ZONE itself. (e.g., if Q.ZONE is "example.com",
      RR.NAME can be "sub.example.com" or "example.com").

      b.  Q.NAME MUST be a sub-domain of RR.NAME, or RR.NAME itself.
      (e.g., if RR.NAME is "sub.example.com", Q.NAME can be
      "host.sub.example.com" or "sub.example.com").

      c.  An NS record for Q.ZONE itself (RR.NAME equals Q.ZONE) is
      considered in-bailiwick.

      d.  NS records for zones that are not superdomains of or equal to
      Q.NAME are generally out-of-bailiwick for positive responses, but
      may be relevant for referrals if they are closer to Q.NAME than
      Q.ZONE.

   AuthS2:
      More precisely, for an NS record (RR.NAME, RR.DATA points to
      NSDNAME) in the authority section of a response from a server
      authoritative for Q.ZONE, where the query was for Q.NAME: The NS
      record is in-bailiwick if RR.NAME is an ancestor of Q.NAME (or
      Q.NAME itself) and RR.NAME is a descendant of Q.ZONE (or Q.ZONE
      itself).  Example: Q.NAME = www.sub.example.com, Q.ZONE =
      example.com.  An NS record for sub.example.com is in-bailiwick.
      An NS record for example.com is in-bailiwick.  An NS record for
      com is NOT in-bailiwick if provided by the example.com server.

   AuthS3:
      For an SOA record in the authority section (typically for negative
      answers or NXDOMAIN), RR.NAME MUST be a superdomain of or equal to
      Q.NAME, and also a subdomain of or equal to Q.ZONE.

   AuthS4:
      Records in the authority section that do not meet these criteria
      MUST be discarded and NOT cached.  This prevents the V1
      vulnerability where a response for attacker.com (Q.NAME) with
      Q.ZONE set to . could inject an NS record for com.  into the
      authority section.

3.3.3.  Additional Section

   The additional section typically contains address records (A/AAAA)
   for nameservers listed in the authority or answer sections (glue
   records), or other records deemed helpful by the authoritative
   server.

   AddS1:




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      For an RR in the additional section to be considered in-
      bailiwick:

      a.  It MUST be "closely related" to an RR that is itself in-
      bailiwick in the answer or authority sections.  "Closely related"
      typically means RR.NAME is the RDATA of an in- bailiwick NS record
      (glue for a nameserver name) or an in- bailiwick MX or SRV record.

      b.  Specifically for glue records (A/AAAA for an NSDNAME appearing
      in an in-bailiwick NS record's RDATA): RR.NAME (the nameserver's
      name) MUST be within the zone being delegated by that NS record
      (i.e., a sub-domain of or equal to the owner name of the NS
      record) or within Q.ZONE.  Glue for out-of-zone nameservers is
      permissible but the address records themselves are only
      authoritative if they are also within Q.ZONE.  Non-authoritative
      glue may be cached but should be treated with lower trust
      [RFC2181].

   AddS2:
      Records in the additional section that are not closely related to
      in-bailiwick records in other sections, or whose RR.NAME is not
      justified by Q.ZONE or a valid delegation, MUST be discarded and
      NOT cached.

3.4.  CNAME Chasing

   When a resolver receives a CNAME (or DNAME) record in response to a
   query for Q.NAME:

   CN1:
      The CNAME/DNAME record itself MUST be validated as per
      Section 3.3.1. (i.e., RR.NAME must match Q.NAME).

   CN2:
      The resolver then initiates a new query for the canonical name
      (the target of the CNAME/DNAME).  The Q.ZONE for this new query
      MUST be determined based on the new Q.NAME (the canonical name) as
      per rules in Section 3.2.1.  It MUST NOT simply inherit the Q.ZONE
      of the original query if the canonical name falls into a different
      bailiwick context.

   CN3:
      Resolvers MUST validate the entire CNAME chain.  Each CNAME in the
      chain must point to a name for which the subsequent CNAME or the
      final answer is in-bailiwick with respect to the Q.ZONE
      established for that specific lookup in the chain.  This prevents
      exploitation of CNAMEs to inject unrelated data (addressing V2
      from [MAGINOTDNS]).



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4.  Bailiwick Checking in Conditional DNS Servers (CDNS)

4.1.  Cache Interaction and Integrity

   CDNS often use a shared global cache for records obtained via both
   recursive resolution and forwarding.  This presents a significant
   risk if bailiwick checks for forwarded data are weaker.

   CDNS1:
      If a CDNS shares a cache between its recursive resolver component
      and its forwarding component, any RR considered for caching from a
      forwarded response MUST undergo bailiwick checks that are at least
      as stringent as those defined for recursive resolution mode
      (Section 3.2.1 and Section 3.3).

   CDNS2:
      Specifically, when a response is received from an upstream
      forwarder, and Q.NAME was part of a $Z_F$:

      a.  Q.ZONE for validating this response MUST NOT be assumed to be
      "." by default if the cache is shared.

      b.  Q.ZONE SHOULD be determined based on the specific $Z_F$ that
      Q.NAME matched, or based on knowledge of the upstream forwarder's
      authoritative scope if the forwarder is not a full recursive
      resolver itself.

      c.  If the upstream forwarder is a recursive resolver, the CDNS
      MAY rely on the upstream resolver's bailiwick checks ONLY IF the
      CDNS itself does not cache the response or if its caching is
      strictly partitioned from the recursive resolver's cache.  If
      cached in a shared manner, the CDNS MUST re-validate.

   CDNS3:
      To prevent the V1 vulnerability in CDNS, if Q.NAME is in $Z_F$ and
      Q.ZONE is determined (e.g., as $Z_F$ itself or an ancestor),
      records in the authority and additional sections of the response
      from the forwarder MUST be validated against this Q.ZONE as per
      Section 3.3.2 and Section 3.3.3.  For example, if $Z_F$ is
      corp.example.com and a query for printer.corp.example.com is
      forwarded, the response MUST NOT be allowed to cache an NS record
      for .com in the authority section if Q.ZONE was effectively
      corp.example.com.








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4.2.  Forwarding Fallback Considerations

   Some CDNS implement a fallback mechanism where if a forwarded query
   fails (e.g., timeout), the CDNS might attempt to resolve it
   recursively.

   CDNS4:
      If a query originally intended for forwarding (in $Z_F$) falls
      back to recursive resolution, the recursive resolution process
      MUST determine its Q.ZONE and apply bailiwick checks
      independently, as per Section 3.2.1 and Section 3.3.  It MUST NOT
      carry over any relaxed bailiwick assumptions from the failed
      forwarding attempt.

5.  Security Considerations

   The enhanced bailiwick checking rules specified in this document are
   intended to mitigate several DNS cache poisoning attack vectors,
   particularly those identified in [MAGINOTDNS] that exploit
   ambiguities or weaknesses in current bailiwick implementations.

   By requiring a more precise determination of Q.ZONE, especially in
   forwarding mode and within CDNS, these rules make it harder for an
   attacker to inject out-of-bailiwick NS records for parent zones (like
   TLDs) or unrelated zones.  Stricter validation of authority and
   additional section records based on a correctly scoped Q.ZONE is key.

   Proper CNAME chain validation with appropriate Q.ZONE adjustments at
   each step helps prevent attacks that leverage CNAMEs to introduce
   malicious data for the canonical target.

   For CDNS, ensuring that data entering a shared cache from forwarding
   operations is subject to rigorous bailiwick checks equivalent to
   those in recursive mode is crucial to prevent cross-mode cache
   pollution.

   While these measures significantly improve resilience against certain
   cache poisoning techniques, they do not replace the need for DNSSEC
   ([RFC4033], [RFC4034], [RFC4035]).  DNSSEC provides cryptographic
   assurance of data origin and integrity and remains the most robust
   defense against cache poisoning.  The rules in this document provide
   defense-in-depth and are particularly important for zones that are
   not DNSSEC-signed or for resolvers that do not validate DNSSEC
   signatures.







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   Implementation of these stricter rules may cause some currently
   accepted (but technically out-of-bailiwick) data from misconfigured
   authoritative servers to be rejected.  This is generally desirable
   for security but operators should be aware of potential compatibility
   issues with non-compliant servers during rollout.

6.  IANA Considerations

   This document does not require any IANA actions.

7.  References

7.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
              <https://www.rfc-editor.org/info/rfc1034>.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
              November 1987, <https://www.rfc-editor.org/info/rfc1035>.

   [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/info/rfc2119>.

   [RFC2181]  Elz, R. and R. Bush, "Clarifications to the DNS
              Specification", RFC 2181, DOI 10.17487/RFC2181, July 1997,
              <https://www.rfc-editor.org/info/rfc2181>.

   [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/info/rfc8174>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", RFC 8499, DOI 10.17487/RFC8499, January
              2019, <https://www.rfc-editor.org/info/rfc8499>.

7.2.  Informative References

   [MAGINOTDNS]
              Li, X., Lu, C., Liu, B., Zhang, Q., Li, Z., Duan, H., and
              Q. Li, "The Maginot Line: Attacking the Boundary of DNS
              Caching Protection", Proceedings of the 32nd USENIX
              Security Symposium , August 2023,
              <https://www.usenix.org/conference/usenixsecurity23/
              presentation/li-xiang>.



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   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, DOI 10.17487/RFC4033, March 2005,
              <https://www.rfc-editor.org/info/rfc4033>.

   [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "Resource Records for the DNS Security Extensions",
              RFC 4034, DOI 10.17487/RFC4034, March 2005,
              <https://www.rfc-editor.org/info/rfc4034>.

   [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/info/rfc4035>.

   [RFC5452]  Hubert, A. and R. van Mook, "Measures for Making DNS More
              Resilient against Forged Answers", RFC 5452,
              DOI 10.17487/RFC5452, January 2009,
              <https://www.rfc-editor.org/info/rfc5452>.

   [RFC6672]  Rose, S. and W. Wijngaards, "DNAME Redirection in the
              DNS", RFC 6672, DOI 10.17487/RFC6672, June 2012,
              <https://www.rfc-editor.org/info/rfc6672>.

   [SADDNS]   Man, K., Qian, Z., Wang, Z., Zheng, X., Huang, Y., and H.
              Duan, "DNS Cache Poisoning Attack Reloaded: Revolutions
              with Side Channels", Proceedings of the 2020 ACM SIGSAC
              Conference on Computer and Communications Security (CCS
              '20) , November 2020.

   [KAMбычноSKY]
              Kaminsky, D., "It's The End Of The Cache As We Know It",
              Black Hat USA 2008 , 2008.

   [POISONOVERFWD]
              Zheng, X., Lu, C., Peng, J., Yang, Q., Zhou, D., Liu, B.,
              Man, K., Hao, S., Duan, H., and Z. Qian, "Poison Over
              Troubled Forwarders: A Cache Poisoning Attack Targeting
              DNS Forwarding Devices", Proceedings of the 29th USENIX
              Security Symposium , August 2020,
              <https://www.usenix.org/conference/usenixsecurity20/
              presentation/zheng>.

   [HITCHHIKERDNS]
              Son, S. and V. Shmatikov, "The Hitchhiker's Guide to DNS
              Cache Poisoning", Proceedings of the 2010 ACM SIGSAC
              Conference on Computer and Communications Security (CCS
              '10) , October 2010.



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Authors' Addresses

   Yuqi Qiu
   Nankai University
   38 Tongyan Road
   Tianjin
   Tianjin, 300355
   China
   Email: norahqiu@163.com


   Xiang Li
   Nankai University
   38 Tongyan Road
   Tianjin
   Tianjin, 300355
   China
   Email: lixiang@nankai.edu.cn

































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