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The RHEL 8 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.


Finding ID Version Rule ID IA Controls Severity
V-230252 RHEL-08-010291 SV-230252r599778_rule Medium
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 8 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/openssh.config file. By specifying a cipher list with the order of ciphers being in a “strongest to weakest” orientation, the system will automatically attempt to use the strongest cipher for securing SSH connections. Satisfies: SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174, SRG-OS-000125-GPOS-00065
Red Hat Enterprise Linux 8 Security Technical Implementation Guide 2020-11-25


Check Text ( C-32921r567502_chk )
Verify the SSH daemon is configured to use only ciphers employing FIPS 140-2-approved algorithms:

Verify that system-wide crypto policies are in effect:

$ sudo grep -i crypto_policy /etc/sysconfig/sshd

# crypto_policy=

If the "crypto_policy" is not commented out and is defined, this is a finding.

Verify which system-wide crypto policy is in use:

$ sudo update-crypto-policies --show


Check that the ciphers in the back-end configurations are FIPS 140-2-approved algorithms with the following command:

$ sudo grep -i ciphers /etc/crypto-policies/back-ends/openssh.config /etc/crypto-policies/back-ends/opensshserver.config

/etc/crypto-policies/back-ends/openssh.config:Ciphers aes256-ctr,aes192-ctr,aes128-ctr

If the cipher entries in the "openssh.config" and "opensshserver.config" files have any ciphers other than "aes256-ctr,aes192-ctr,aes128-ctr", the order differs from the example above, if they are missing, or commented out, this is a finding.
Fix Text (F-32896r599777_fix)
Configure the RHEL 8 SSH daemon to use only ciphers employing FIPS 140-2-approved algorithms with the following command:

$ sudo fips-mode-setup --enable

Next, update the "/etc/crypto-policies/back-ends/openssh.config" and "/etc/crypto-policies/back-ends/opensshserver.config" files to include these ciphers employing FIPS 140-2-approved algorithms:

/etc/crypto-policies/back-ends/openssh.config:Ciphers aes256-ctr,aes192-ctr,aes128-ctr

A reboot is required for the changes to take effect.