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
Do you still have questions? Questions regarding this advisory
should go to security-offi...@isc.org. To report a new issue,
please encrypt your message using security-offi...@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
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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