title: An error in TSIG authentication can permit unauthorized dynamic updates
description: An attacker who is able to send and receive messages to an authoritative DNS server and who has knowledge of a valid TSIG key name for the zone and service being targeted may be able to manipulate BIND into accepting an unauthorized dynamic update. Affects BIND 9.4.0->9.8.8, 9.9.0->9.9.10-P1, 9.10.0->9.10.5-P1, 9.11.0->9.11.1-P1, 9.9.3-S1->9.9.10-S2, 9.10.5-S1->9.10.5-S2.
problem types: A server that relies solely on TSIG keys with no other address-based ACL protection could be vulnerable to malicious zone content manipulation using this technique.
Note that the local update policy (configured with "update-policy local;" in named.conf) implicitly defines a key with a known key name (local-ddns) and default algorithm and no IP-based access controls on the zone updates.  In conjunction with this failure in TSIG verification, "update-policy local" is potentially very dangerous.
affected:
{
product: BIND 9
vendor: ISC
versions:
status: affected, version: 9.4.0->9.8.8, 9.9.0->9.9.10-P1, 9.10.0->9.10.5-P1, 9.11.0->9.11.1-P1, 9.9.3-S1->9.9.10-S2, 9.10.5-S1->9.10.5-S2
}
metrics:
cvssV3_0: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: NONE
baseScore: 7.5
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: HIGH
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
version: 3.0
]
solutions:  Upgrade to the patched release most closely related to your current version of BIND. These can all be downloaded from http://www.isc.org/downloads.
BIND 9 version 9.9.10-P2
BIND 9 version 9.10.5-P2
BIND 9 version 9.11.1-P2
BIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.
BIND 9 version 9.9.10-S3
BIND 9 version 9.10.5-S3
workarounds: The effects of this vulnerability can be mitigated by using Access Control Lists (ACLs) that require both address range validation and use of TSIG authentication in conjunction.  For information on how to configure this type of compound authentication control, please see: https://kb.isc.org/article/AA-00723/0/Using-Access-Control-Lists-ACLs-with-both-addresses-and-keys.html.
Administrators who have made use of named.conf option "update-policy local;" should patch their servers as soon as possible and if this is not possible should replace the update-policy configuration statement with an allow-update statement implementing the key requirement for updates but additionally imposing an IP ACL limitation, e.g.:
allow-update { !{ !localhost; }; key local-ddns; };