The Cisco ASA must be configured to use a Diffie-Hellman (DH) Group of 16 or greater for Internet Key Exchange (IKE) Phase 1.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
high	V-239957	SRG-NET-000074-VPN-000250	CASA-VN-000210	SV-239957r916149_rule	2024-08-22	2

Description
Use of an approved DH algorithm ensures the IKE (Phase 1) proposal uses FIPS-validated key management techniques and processes in the production, storage, and control of private/secret cryptographic keys. The security of the DH key exchange is based on the difficulty of solving the discrete logarithm from which the key was derived. Hence, the larger the modulus, the more secure the generated key is considered to be.

Description

Use of an approved DH algorithm ensures the IKE (Phase 1) proposal uses FIPS-validated key management techniques and processes in the production, storage, and control of private/secret cryptographic keys. The security of the DH key exchange is based on the difficulty of solving the discrete logarithm from which the key was derived. Hence, the larger the modulus, the more secure the generated key is considered to be.

ℹ️ Check
Review the ASA configuration to determine if DH Group of 16 or greater has been specified for IKE Phase 1 as shown in the example below. crypto ikev2 policy 1 encryption aes-256 … group 24 If DH Group of 16 or greater has not been specified for IKE Phase 1, this is a finding.

✔️ Fix
Configure the ASA to use a DH Group of 16 or greater as shown in the example below. ASA1(config)# crypto ikev2 policy 1 ASA1(config-ikev2-policy)# group 24