Operational Notification: Extremely large zone transfers can result in corrupted journal files or server process termination

[Michael McNally]

Summary:

   In versions of BIND released prior to July 2018 (before BIND
   9.9.13, 9.10.8, 9.11.4, 9.12.2, and BIND 9.13.1) it is possible
   for extraordinarily large zone transfers to cause several related
   problems, with possible outcomes including corrupted journal
   files or server exit due to assertion failure.

Posting date:        03 July 2018
Program Impacted:    BIND
Versions affected:   9.0.x -> 9.8.8, 9.9.0 -> 9.9.12, 9.10.0 -> 9.10.7,
                     9.11.0 -> 9.11.3, 9.12.0 -> 9.12.1, and versions
                     9.13.0 -> 9.13.1 of the 9.13 development branch

Description:

   A problem in named can potentially lead to corrupted journal
   files when handling extraordinarily large zone transfers.

Impact:

   This problem potentially affects authoritative servers providing
   slave service for zones if the server accepts zone data via
   incremental zone transfer (IXFR) from a master source or if a
   large zone transfer (AXFR) is received and ixfr-from-differences
   is not set to "no" (the default setting is "yes", and possible
   values are "yes", "no", "slave", and "master").

   We warned of a similar class of problems in 2016 in this previous
   Operational Notification "A party that is allowed control over
   zone data can overwhelm a server by transferring huge quantities
   of data." (https://kb.isc.org/article/AA-01390)

Workarounds:

   Like any unvalidated input, zone transfers are a potential source
   of risk for servers under any circumstances.  BIND therefore
   supports a variety of mechanisms to control zone transfer
   permissions.  Permission to transfer can be restricted to trusted
   servers using IP-address-based ACLs or shared secrets (TSIG keys)
   or both.  Under most circumstances a slave server should not
   encounter this defect when receiving data from a trusted server,
   but it can be prevented entirely by forbidding incremental zone
   transfer as a zone data transfer mechanism.  It may be preferable
   to instead set a reasonable limit for the number of records which
   may be in a zone (using the max-records parameter) which should
   also prevent accidentally encountering this defect.

   Servers which must accept zone data from untrusted sources (for
   example, when seconding zones for other parties) are at slightly
   higher risk if a party decides to deliberately feed a dangerously
   large zone transfer.  Operators of servers which must accept
   untrusted zone data should consider limiting zone size using
   max-records, setting "ixfr-from-differences no;", or upgrading
   to a version of BIND which will reject dangerously large transfers.

Active exploits:

   No known active exploits.

Solution:

   It is our opinion that most customers do not need to worry about
   this issue unless they accept zone data via zone transfer from
   untrusted sources, but we have included changes in upcoming
   maintenance releases of BIND which will prevent the condition
   from being reached.

   Maintenance releases of BIND issued on or after 4 July 2018 will
   contain change #4984, which will cause BIND to reject an
   extraordinarily large IXFR if it is potentially large enough to
   corrupt the journal file. These release candidates are available
   now via https://www.isc.org/downloads and the change will be
   included in future versions of BIND

    BIND 9 version 9.9.13rc2
    BIND 9 version 9.10.8rc2
    BIND 9 version 9.11.4rc2
    BIND 9 version 9.12.2rc2


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Note:

   ISC patches only currently supported versions. When possible we
   indicate EOL versions affected.  (For current information on
   which versions are actively supported, please see
   http://www.isc.org/downloads/).

ISC Security Vulnerability Disclosure Policy:

   Details of our current security advisory policy and practice can
   be found here: https://kb.isc.org/article/AA-00861

This Knowledge Base article https://kb.isc.org/article/AA-01627
is the complete and official security advisory document.

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