Title

RHEL 9 must implement DOD-approved encryption ciphers to protect the confidentiality of SSH client 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, non-organization-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 system-wide 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 system-wide crypto policies are in effect with the following command: $ sudo grep 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 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 system-wide crypto policies by running the following commands: $ sudo dnf reinstall openssh-clients

Additional Identifiers

Rule ID: SV-257988r925951_rule

Vulnerability ID: V-257988

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

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.