The Cisco VPN remote access server must be configured to use AES256 or greater encryption for the Internet Key Exchange (IKE) Phase 1 to protect confidentiality of remote access sessions.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
high	V-239979	SRG-NET-000317-VPN-001090	CASA-VN-000640	SV-239979r987747_rule	2024-08-22	2

Description
Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. Remote access is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. AES is the FIPS-validated cipher block cryptographic algorithm approved for use in DOD. For an algorithm implementation to be listed on a FIPS 140-2/140-3 cryptographic module validation certificate as an approved security function, the algorithm implementation must meet all the requirements of FIPS 140-2/140-3 and must successfully complete the cryptographic algorithm validation process. Currently, NIST has approved the following confidentiality modes to be used with approved block ciphers in a series of special publications: ECB, CBC, OFB, CFB, CTR, XTS-AES, FF1, FF3, CCM, GCM, KW, KWP, and TKW.

Description

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. Remote access is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. AES is the FIPS-validated cipher block cryptographic algorithm approved for use in DOD. For an algorithm implementation to be listed on a FIPS 140-2/140-3 cryptographic module validation certificate as an approved security function, the algorithm implementation must meet all the requirements of FIPS 140-2/140-3 and must successfully complete the cryptographic algorithm validation process. Currently, NIST has approved the following confidentiality modes to be used with approved block ciphers in a series of special publications: ECB, CBC, OFB, CFB, CTR, XTS-AES, FF1, FF3, CCM, GCM, KW, KWP, and TKW.

ℹ️ Check
Verify IKE Phase 1 is set to use an AES256 or greater encryption algorithm as shown in the example below. crypto ipsec ikev2 ipsec-proposal IPSEC_TRANS protocol esp encryption aes-256 If the value of the encryption algorithm for IKE Phase 1 is not set to use an AES256 or greater algorithm, this is a finding.

✔️ Fix
Configure the ASA to use AES256 or greater encryption algorithm for IKE Phase 1 as shown in the example below. ASA1(config)# crypto ikev2 policy 1 ASA1(config-ikev2-policy)# encryption aes-256