title: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c
description: In BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3, If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash. Servers that 'forward only' are not affected.
problem types: While query forwarding and QNAME minimization are mutually incompatible, BIND did sometimes allow QNAME minimization when continuing with recursion after 'forward first' did not result in an answer. In these cases the data used by QNAME minimization might be inconsistent, leading to an assertion failure, causing the server to exit.  Affects BIND 9.14.0 -> 9.16.5, 9.17.0 -> 9.17.3
affected:
{
product: BIND9
vendor: ISC
versions:
changes: [at: 9.16.6, status: unaffected], lessThan: *, status: affected, version: 9.14.0, versionType: custom
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 7.5
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: NONE
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
version: 3.1
]
exploits: We are not aware of any active exploits.
solutions: Upgrade to the patched release most closely related to your current version of BIND:
BIND 9.16.6
BIND 9.17.4
workarounds: No workarounds known.