cis-gcp-foundations-3.5

DevOps & Security

Ensure That RSASHA1 Is Not Used for the Zone-Signing Key in Cloud DNS DNSSEC

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3.5 Ensure That RSASHA1 Is Not Used for the Zone-Signing Key in Cloud DNS DNSSEC (Automated)

Profile Applicability

Level 1

Description

NOTE: Currently, the SHA1 algorithm has been removed from general use by Google, and, if being used, needs to be whitelisted on a project basis by Google and will also, therefore, require a Google Cloud support contract.

DNSSEC algorithm numbers in this registry may be used in CERT RRs. Zone signing (DNSSEC) and transaction security mechanisms (SIG(0) and TSIG) make use of particular subsets of these algorithms. The algorithm used for key signing should be a recommended one and it should be strong.

Rationale

DNSSEC algorithm numbers in this registry may be used in CERT RRs. Zone signing (DNSSEC) and transaction security mechanisms (SIG(0) and TSIG) make use of particular subsets of these algorithms.

The algorithm used for key signing should be a recommended one and it should be strong. When enabling DNSSEC for a managed zone, or creating a managed zone with DNSSEC, the DNSSEC signing algorithms and the denial-of-existence type can be selected. Changing the DNSSEC settings is only effective for a managed zone if DNSSEC is not already enabled. If the need exists to change the settings for a managed zone where it has been enabled, turn DNSSEC off and then re-enable it with different settings.

Audit

From Google Cloud CLI

Ensure the property algorithm for keyType zone signing is not using RSASHA1.

gcloud dns managed-zones describe --format="json(dnsName,dnssecConfig.state,dnssecConfig.defaultKeySpecs)"

Remediation

From Google Cloud CLI

If the need exists to change the settings for a managed zone where it has been enabled, DNSSEC must be turned off and then re-enabled with different settings. To turn off DNSSEC, run following command:

gcloud dns managed-zones update ZONE_NAME --dnssec-state off

To update zone-signing for a reported managed DNS Zone, run the following command:

gcloud dns managed-zones update ZONE_NAME --dnssec-state on --ksk-algorithm KSK_ALGORITHM --ksk-key-length KSK_KEY_LENGTH --zsk-algorithm ZSK_ALGORITHM --zsk-key-length ZSK_KEY_LENGTH --denial-of-existence DENIAL_OF_EXISTENCE

Supported algorithm options and key lengths are as follows:

Algorithm	KSK Length	ZSK Length
RSASHA1	1024,2048	1024,2048
RSASHA256	1024,2048	1024,2048
RSASHA512	1024,2048	1024,2048
ECDSAP256SHA256	256	384
ECDSAP384SHA384	384	384

References

https://cloud.google.com/dns/dnssec-advanced#advanced_signing_options

Additional Information

RSASHA1 zone-signing support may be required for compatibility reasons.
The remediation CLI works well with gcloud-cli version 221.0.0 and later.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v8	4.2 Establish and Maintain a Secure Configuration Process for Network Infrastructure	x	x	x
v7	11.1 Maintain Standard Security Configurations for Network Devices		x	x