Title

RHEL 9 must implement DOD-approved encryption ciphers to protect the confidentiality of SSH connections. (Cat II impact)

Discussion

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. RHEL 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.

Check Content

Verify that RHEL 9 implements DOD-approved encryption ciphers for SSH connections. Verify that the SSH configuration files include the path to the systemwide policy with the following command: $ sudo grep -R Include /etc/ssh/sshd_config /etc/ssh/sshd_config.d/ /etc/ssh/sshd_config:Include /etc/ssh/sshd_config.d/*.conf /etc/ssh/sshd_config.d/50-redhat.conf:Include /etc/crypto-policies/back-ends/opensshserver.config If "Include /etc/ssh/sshd_config.d/*.conf" or "Include /etc/crypto-policies/back-ends/opensshserver.config" are not included in the system sshd config or if the file "/etc/ssh/sshd_config.d/50-redhat.conf" is missing, this is a finding.

Fix Text

Configure the RHEL 9 SSH daemon to use systemwide crypto policies. Reinstall OpenSSH client package contents with the following command: $ sudo dnf -y reinstall openssh

Additional Identifiers

Rule ID: SV-257988r1051234_rule

Vulnerability ID: V-257988

Group Title: SRG-OS-000250-GPOS-00093

Expert Comments

CCIs tied to check.

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