title: A flaw in the "deny-answer-aliases" feature can cause an assertion failure in named
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 assertion failure in name.c. Affects BIND 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.
problem types: Accidental or deliberate triggering of this defect will cause a REQUIRE assertion failure in named, causing the named process to stop execution and resulting in denial of service to clients.
affected:
{
product: BIND 9
vendor: ISC
versions:
status: affected, version: BIND 9  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
}
metrics:
cvssV3_0: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 7.5
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: NONE
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
version: 3.0
]
solutions: 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
workarounds: This vulnerability can be avoided by disabling the "deny-answer-aliases" feature if it is in use.