xref: /src/external/mpl/bind/dist/doc/notes/notes-9.20.26.rst

.. Copyright (C) Internet Systems Consortium, Inc. ("ISC")
..
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Notes for BIND 9.20.26
----------------------

Security Fixes
~~~~~~~~~~~~~~

- Correct verification of NSEC3 signer name. :cve:`2026-10723`

  Previously, :iscman:`named` accepted child-zone NSEC3 records where
  the first label equaled the hash of the parent zone as valid
  parent-zone closest encloser proofs. This has been fixed.

  ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing
  this vulnerability to our attention. :gl:`#5874`

- Malformed DNSKEY records could trigger an assertion. :cve:`2026-10822`

  Previously, ``dns_name_fromwire()`` did not honor the record boundary
  when reading names from the wire, allowing malformed records to be
  accepted when they should not have been. In particular, malformed
  DNSKEY records could trigger an assertion failure when being printed.
  This has been fixed. :gl:`#6004`

- Fix handling of RPZ CNAME expansion that returns too-long name.
  :cve:`2026-11331`

  Previously, if the expansion of a wildcard CNAME RPZ policy resulted
  in a name that exceeded the length limit, a self-referential CNAME and
  the original address record were returned, allowing the policy to be
  bypassed. In branches up to 9.20 this also left query processing in an
  inconsistent state, which could trigger an assertion failure.
  :iscman:`named` now returns a YXDOMAIN response, without the address.

  ISC would like to thank Laith Mash'al (0xmshal) for bringing this
  vulnerability to our attention. :gl:`#5856`

- Prevent excessive validation work from crafted negative responses.
  :cve:`2026-11605`

  Previously, a validating resolver could be made to perform a large
  amount of DNSSEC validation work in response to a single answer,
  consuming excessive CPU. A malicious authoritative server could
  trigger this by returning a signed negative answer (NXDOMAIN or
  NODATA) padded with many denial-of-existence proof records, which the
  resolver continued to verify beyond its per-query validation limit. It
  now enforces that limit on negative answers and returns SERVFAIL once
  the limit is reached. :gl:`#4463`

- Prevent cache exhaustion under sustained attack. :cve:`2026-11622`

  Cache memory could become exhausted with expired entries whose memory
  was not released, due to a sustained attack on the same DNS name that
  prevented the cleanup. This has been fixed. :gl:`#4760`

- Stop accepting invalid signed wildcard records. :cve:`2026-11721`

  Signed wildcard responses in which the Labels field in the RRSIG
  record was less than the number of labels in the Signer Name field
  were being incorrectly accepted. This in turn broke
  :namedconf:ref:`synth-from-dnssec`, which depends on such records
  being correctly validated. This has been fixed.

  ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing
  this vulnerability to our attention. :gl:`#5871`

- Do not assert for some specific CNAME and DNAME queries.
  :cve:`2026-12617`

  A bug in the resolver's handling of certain cached DNAME and CNAME
  responses could cause :iscman:`named` to trigger an assertion failure
  and exit. An attacker controlling a domain name and the authoritative
  DNS server it was hosted on could exploit this behavior to cause a
  denial-of-service. This has been fixed.

  ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing
  this vulnerability to our attention. :gl:`#5946`

- Prevent crash from malformed NSEC/NSEC3 response. :cve:`2026-13204`

  An assertion could be triggered by an improperly signed NOQNAME proof.
  This has been fixed.

  ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing
  this vulnerability to our attention. :gl:`#5985`

- Fix DNSSEC validation bypass via out-of-zone NSEC Next Field.
  :cve:`2026-13321`

  Previously, a malicious zone with out-of-zone NSEC next-owner names
  could cause a DNSSEC-validating resolver to cache such a record and,
  if :namedconf:ref:`synth-from-dnssec` was enabled, to generate
  negative answers for any zone that was covered by the range. This has
  been fixed.

  ISC would like to thank Qifan Zhang of Palo Alto Networks for bringing
  this vulnerability to our attention. :gl:`#5873`

- Reclaim memory promptly when DNSSEC validations are canceled.

  When a resolver is flooded with queries that require DNSSEC validation
  - for example during a random-subdomain attack - many of those
  validations are canceled before they complete. Previously, a canceled
  validation still kept its place in the internal work queue and held
  the associated response in memory until that queued work eventually
  ran, so memory could climb sharply under sustained load. The internal
  work queue is now dropped as soon as the validation is canceled,
  releasing the memory it was holding. :gl:`#4760`

Removed Features
~~~~~~~~~~~~~~~~

- Remove the secondary validator in ``query.c``.

  Previously, when the additional section of a response was being
  populated, if cached data was found with pending trust, it would be
  opportunistically validated. The code implementing this validation was
  not quite formally correct. Rather than fixing it, the code has been
  removed: RRsets with pending trust are now omitted from responses.
  :gl:`#5966` :gl:`#5968` :gl:`#5972`

Bug Fixes
~~~~~~~~~

- Fix a bug in DNS UPDATE processing with
  :namedconf:ref:`inline-signing` enabled.

  In rare cases the :iscman:`named` process could terminate unexpectedly
  when processing authorized DNS UPDATE messages in quick succession
  that were updating a zone with :namedconf:ref:`inline-signing`
  enabled. This has been fixed. :gl:`#5816`

- Properly detect private records before copying.

  Previously, an assertion was triggered when trying to copy a private
  record to a buffer for modification. :iscman:`named` now extends the
  private type detection and copies the contents after rejecting invalid
  private records. :gl:`#5857`

- Tighten referral DS acceptance.

  Previously, :iscman:`named` accepted DS records for sibling zones when
  it shouldn't have. This has been fixed. :gl:`#5870`

- Don't synthesize negative responses with pending NSEC.

  If an NSEC record has not yet been validated and is cached with trust
  pending, :iscman:`named` no longer uses it to synthesize negative
  responses. :gl:`#5872` :gl:`#5887` :gl:`#5977`

- Check that an NSEC signer is at or above the name to be validated.

  A check has been added to ensure that an NSEC record being used as a
  proof of nonexistence for a given name is not signed by a name lower
  in the DNS hierarchy than the one in question. :gl:`#5876`

- Don't evict DNSSEC-validated cache data on a CD=1 NXDOMAIN.

  When a client sent a query with the checking-disabled (CD) bit set and
  the answer was NXDOMAIN, the resolver cached that unvalidated negative
  response and discarded any DNSSEC-validated records it already held
  for the same name, even though the validated data was more
  trustworthy. A single such response - including a forged one - could
  flush validated records from the cache and force the resolver to fetch
  them again. The resolver now checks the trust level of the existing
  data first and leaves the cache unchanged when it is already
  validated. :gl:`#5877`

- Fix a :namedconf:ref:`deny-answer-aliases` configuration bypass issue.

  It was possible to use a maliciously crafted authoritative zone to
  make a :iscman:`named` resolver synthesize a DNAME "alias" that should
  have been rejected by the configured :any:`deny-answer-aliases`
  option. This has been fixed. :gl:`#5930`

- Reject external referrals from forwarders.

  Under a ``forward first;`` policy in a forwarding zone,
  :iscman:`named` could accept NS records above the forward zone apex
  from negative responses. This has been fixed. :gl:`#5937`

- Fix a zone transfer over TLS (XoT) issue when using the opportunistic
  TLS mode.

  The :iscman:`named` process, running as a secondary DNS server and
  configured to transfer a zone from a primary server using an encrypted
  XoT transport in opportunistic TLS mode (i.e. without peer
  certificate/hostname validation), could terminate unexpectedly when
  the TLS ALPN negotiation with the primary server was unsuccessful.
  This has been fixed. :gl:`#5957`

- Unvalidated opt-out NSEC3 could be accepted in insecurity proof.

  When determining whether an insecure delegation was legitimate, NSEC3
  opt-out records which had not yet passed validation could be used.
  This has been fixed. :gl:`#5970`

- Check wildcard signer and NOQNAME signer match.

  A positive wildcard answer, and the NSEC3 proof that the requested
  name doesn't exist in the zone, must both be from the same zone.
  Otherwise, an NSEC3 from an ancestor zone could be used to interfere
  with validation.

  :iscman:`named` now retrieves the signer name from a wildcard
  response's signature. An NSEC3 record cannot be used as a NOQNAME
  proof for the wildcard unless it exactly matches the name one level
  above the NSEC3. :gl:`#5971`

- Fix CNAME resolution failure caused by a cached SERVFAIL response.

  Under certain circumstances, a cached SERVFAIL response could
  incorrectly prevent successful resolution of a CNAME target. This
  could cause resolution failures to persist until the cached SERVFAIL
  entry expired, even when the CNAME target itself was otherwise
  resolvable. This has been fixed. :gl:`#5983`

- Reject unsupported RSA DNSKEY shapes during DNSSEC validation.

  An authoritative server publishing an RSA DNSKEY with an unusually
  large modulus or an exotic public exponent could make each DNSSEC
  signature check on a validating recursive resolver noticeably more
  expensive than for a normally sized key. Such DNSKEYs are now treated
  as invalid. :gl:`#6008`

- Fix a bug in GeoIP2 string matching.

  When using GeoIP2 ACLs (see :any:`acl`), :iscman:`named` could
  incorrectly match a name using a sub-string instead of the full name
  match. This has been fixed. :gl:`#6019`

- Fix DNS-over-HTTPS (DoH) quota configuration issue.

  The :any:`http-listener-clients` and
  :any:`http-streams-per-connection` configuration options could be
  truncated to smaller values (or to ``0``, which means unlimited) when
  very large configuration values in excess of ``65535`` were used. It
  is very unlikely that such large values were used in production, and
  the default values for the affected options are ``300`` and ``100``,
  respectively. This has been fixed. :gl:`#6021`

- Truncated reply to a TSIG query no longer stalls the resolver.

  When an upstream server returned a truncated reply to a query that
  :iscman:`named` had signed with TSIG, the resolver could keep waiting
  for a follow-up UDP packet that never arrived, stalling the query
  until it hit the :namedconf:ref:`resolver-query-timeout` and the
  client received no answer. :iscman:`named` now treats any reply it
  cannot authenticate as an immediate failure and returns SERVFAIL right
  away as a defense in depth. :gl:`#6028`

- Ignore updates removing DNSKEY RRset with class ANY.

  When a dynamic update is received that removes the DNSKEY (or CDNSKEY,
  or CDS) RRset, :iscman:`named` now removes all records except the ones
  that are in use for signing the zone. :gl:`#6045`

- Ignore 0-byte reads in the TCP read callback.

  Callbacks for libuv stream reads do not signal zero-length reads as a
  failure signal but rather as EAGAIN/EWOULDBLOCK. This could trigger an
  assertion when a zero-length read was pushed onto a PROXYv2 endpoint
  that had not yet processed the headers, as it expected a non-NULL
  region of positive length. :gl:`#6140`

- Only print per-zone glue stats when :namedconf:ref:`zone-statistics`
  is set to ``full``.

  The code printing query statistics was ignoring the
  :namedconf:ref:`zone-statistics` option. This has been fixed.
  :gl:`#6164`

- CDS/CDNSKEY records were not removed when re-configuring the server.

  When on an :option:`rndc reconfig` the DNSSEC policy changes such that
  it changes the expected CDNSKEY and/or CDS records in the zone, the
  RRset should be updated accordingly. This did not happen when removing
  digests from the configuration, or setting ``cdnskey no;``. This has
  been fixed. :gl:`#6166`

- Fix a crash when querying an empty non-terminal in a wildcard zone in
  RBTDB.

  A query for an empty non-terminal in a wildcard zone served from the
  RBT zone database could abort :iscman:`named` with an assertion
  failure. It now returns the correct NODATA answer. :gl:`#6170`

- Stop reusing outgoing TCP connections the peer has already closed.

  Previously, :iscman:`named` could hand a new query to an idle
  forwarder/upstream TCP or TLS connection that the peer had already
  closed, causing the query to fail (and CLOSE-WAIT sockets to pile up).
  Idle reused connections are now watched, so a close is noticed and the
  connection is dropped instead of reused. A new
  :namedconf:ref:`tcp-reuse-timeout` option controls how long an idle
  outgoing connection is kept open for reuse (default 5 seconds).
  :gl:`#6171`

- Fix DNSSEC validation failures for names under an apex DNAME.

  DNSSEC validation could fail with SERVFAIL for names covered by a
  DNAME at the apex of a signed zone, unless the zone's keys were
  already validated in the cache. This regression was introduced by the
  recent fix for resolver stalls on CNAME responses to DS queries, and
  has now been addressed. :gl:`#6176`