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The Cisco ASA VPN remote access server must be configured to use Advanced Encryption Standard (AES) encryption for the IPsec security association to protect the confidentiality of remote access sessions.


Finding ID Version Rule ID IA Controls Severity
V-239980 CASA-VN-000650 SV-239980r666346_rule High
Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. Remote access is access to DoD non-public information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. A block cipher mode is an algorithm that features the use of a symmetric key block cipher algorithm to provide an information service, such as confidentiality or authentication. 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 cryptographic module validation certificate as an approved security function, the algorithm implementation must meet all the requirements of FIPS 140-2 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.
Cisco ASA VPN Security Technical Implementation Guide 2021-08-16


Check Text ( C-43213r666344_chk )
Verify all IPsec proposals are set to use the AES encryption algorithm as shown in the example below.

crypto ipsec ikev2 ipsec-proposal IPSEC_TRANS
protocol esp encryption aes-192

If the value of the encryption algorithm for any IPsec proposal is not set to use an AES algorithm, this is a finding.
Fix Text (F-43172r666345_fix)
Configure the ASA to use AES encryption algorithm to implement IPsec encryption services as shown in the example below.

ASA2(config)# crypto ipsec ikev2 ipsec-proposal IPSEC_TRANS
ASA2(config-ipsec-proposal)# protocol esp encryption aes-192
ASA2(config-ipsec-proposal)# end