ALMA-09-003540 - AlmaLinux OS 9 SSH server must be configured to use only Message Authentication Codes (MACs) employing FIPS 140-3 validated cryptographic hash algorithms.

Information

Without cryptographic integrity protections, information can be altered by unauthorized users without detection.

Remote access (e.g., RDP) is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, nonorganization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless.

Cryptographic mechanisms used for protecting the integrity of information include, for example, signed hash functions using asymmetric cryptography enabling distribution of the public key to verify the hash information while maintaining the confidentiality of the secret key used to generate the hash.

AlmaLinux OS 9 incorporates systemwide crypto policies by default. The SSH configuration file has no effect on the ciphers, MACs, or algorithms unless specifically defined in the /etc/sysconfig/sshd file. The employed algorithms can be viewed in the /etc/crypto-policies/back-ends/opensshserver.config file.

Solution

Configure the AlmaLinux OS 9 SSH server to use only MACs employing FIPS 140-3 approved algorithms by updating the "/etc/crypto-policies/back-ends/opensshserver.config" file with the following commands:

Note: Before enabling FIPS mode, ensure that the dracut-fips package is installed on the system.

Enable FIPS mode by updating the system's crypto policy with the following command:
$ sudo update-crypto-policies --set FIPS

Note: If FIPS mode has never been enabled on the system, additional steps will need to be conducted. Refer to vendor documentation.

To manually update the MACs in the systemwide SSH configuration, use the following command:
$ sudo sed -i -E '/^MACs/s/.*/MACs [email protected],[email protected],hmac-sha2-512,hmac-sha2-256/' "$(readlink -f /etc/crypto-policies/back-ends/opensshserver.config)"

A reboot is required for the changes to take effect.

See Also

https://workbench.cisecurity.org/benchmarks/0

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-17(2), CAT|II, CCI|CCI-001453, Rule-ID|SV-269119r1050001_rule, STIG-ID|ALMA-09-003540, Vuln-ID|V-269119

Plugin: Unix

Control ID: 5fa44561844683688f3a9e4a29c89f5b505de7bd71026ec42553b2b3d0d78629