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Message-ID: <997e5c81-da6d-b8a9-e384-bb62ff81fffc@isc.org>
Date: Wed, 8 Aug 2018 21:45:43 -0800
From: Michael McNally <mcnally@....org>
To: oss-security@...ts.openwall.com, isc-os-security@...ts.isc.org
Cc: "security-officer@....org" <security-officer@....org>
Subject: CVE-2018-5740: A flaw in the "deny-answer-aliases" feature can cause
an INSIST assertion failure in named
Earlier today ISC disclosed CVE-2018-5740, involving a potential
denial-of-service vector in an uncommonly-used feature of BIND.
Our official security advisory document is posted in the ISC Knowledge Base
at this URL: https://kb.isc.org/article/AA-01639 but for your convenience
the text is provided below.
Patched versions of BIND are available from https://www.isc.org/downloads
Michael McNally
ISC Security Officer
----------
A rarely-used feature in BIND has a flaw which can cause named to
exit with an INSIST assertion failure.
CVE: CVE-2018-5740
Document Version: 2.0
Posting date: 08 August 2018
Program Impacted: BIND
Versions affected: 9.7.0->9.8.8, 9.9.0->9.9.13, 9.10.0->9.10.8,
9.11.0->9.11.4, 9.12.0->9.12.2, 9.13.0->9.13.2
and also versions of BIND 9 Supported Preview Edition
Severity: High (but only for servers on which the
"deny-answer-aliases"
feature is explicitly enabled)
Exploitable: Remotely
Description:
"deny-answer-aliases" is a little-used feature intended to help
recursive server operators protect end users against DNS rebinding
attacks, a potential method of circumventing the security model
used by client browsers. However, a defect in this feature makes
it easy, when the feature is in use, to experience an INSIST
assertion failure in name.c.
Impact:
Accidental or deliberate triggering of this defect will cause
an INSIST assertion failure in named, causing the named process
to stop execution and resulting in denial of service to clients.
Only servers which have explicitly enabled the "deny-answer-aliases"
feature are at risk and disabling the feature prevents exploitation.
CVSS Score: 7.5
CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
For more information on the Common Vulnerability Scoring System and
to obtain your specific environmental score please visit:
https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Workarounds:
This vulnerability can be avoided by disabling the "deny-answer-aliases"
feature if it is in use.
Active exploits:
No known active exploits.
Solution:
Most operators will not need to make any changes unless they are
using the "deny-answer-aliases" feature (which is described in
the BIND 9 Adminstrator Reference Manual section 6.2.)
"deny-answer-aliases" is off by default; only configurations
which explicitly enable it can be affected by this defect.
If you are using "deny-answer-aliases", upgrade to the patched
release most closely related to your current version of BIND.
- 9.9.13-P1
- 9.10.8-P1
- 9.11.4-P1
- 9.12.2-P1
BIND Supported Preview Edition is a special feature preview
branch of BIND provided to eligible ISC support customers.
- 9.11.3-S3
Acknowledgements:
ISC would like to thank Tony Finch of the University of Cambridge
for reporting this issue.
Document Revision History:
1.0 Advance Notification 31 July, 2018
2.0 Public Disclosure 08 August, 2018
Related Documents:
See our BIND9 Security Vulnerability Matrix at
https://kb.isc.org/article/AA-00913 for a complete listing of
Security Vulnerabilities and versions affected.
If you'd like more information on ISC Subscription Support and
Advance Security Notifications, please visit http://www.isc.org/support/.
Do you still have questions? Questions regarding this advisory
should go to security-officer@....org. To report a new issue,
please encrypt your message using security-officer@....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-01639 is
the complete and official security advisory document.
Legal Disclaimer:
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Uncontrolled copies may lack important information, be out of
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