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

  • Updated on 17 Sep 2018
  • 3 minutes to read
  • Contributors 

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 ImpactedBIND

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 version 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 "no", and possible values are "yes", "no", "slave", and "master"). [Please note:  a previous version of this text incorrectly stated that the default setting for ixfr-from-differences was "yes".]

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."

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

Do you still have questions? Questions regarding this advisory should go to security-officer@isc.orgTo report a new issue, please encrypt your message using security-officer@isc.org's PGP key which can be found here: https://www.isc.org/downloads/software-support-policy/openpgp-key/. If you are unable to use encrypted email, you may also report new issues at: https://www.isc.org/community/report-bug/.

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 https://www.isc.org/downloads/). 

ISC Security Vulnerability Disclosure Policy: Details of our current security advisory policy and practice can be found here: ISC Software Defect and Security Vulnerability Disclosure Policy.html

This Knowledgebase article is the complete and official security advisory document.

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