Title

RHEL 9 must implement DOD-approved encryption ciphers to protect the confidentiality of SSH server 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 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 the SSH client is configured to use only ciphers employing FIPS 140-3 approved algorithms with the following command: $ sudo grep -i ciphers /etc/crypto-policies/back-ends/openssh.config Ciphers aes-256-gcm@openssh.com, chacha20-poly1305@openssh.com, aes256-ctr,aes128-gcm@openssh.com,aes128-ctr If the cipher entries in the "openssh.config" file have any ciphers other than "aes-256-gcm@openssh.com, chacha20-poly1305@openssh.com, aes256-ctr,aes128-gcm@openssh.com,aes128-ctr", the order differs from the example above, they are missing, or commented out, this is a finding.

Fix Text

Configure the RHEL 9 SSH client to use only ciphers employing FIPS 140-3 approved algorithms by updating the "/etc/crypto-policies/back-ends/openssh.config" file with the following line: Ciphers aes-256-gcm@openssh.com, chacha20-poly1305@openssh.com, aes256-ctr,aes128-gcm@openssh.com,aes128-ctr A reboot is required for the changes to take effect.

Additional Identifiers

Rule ID: SV-257989r925954_rule

Vulnerability ID: V-257989

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.