The SSH daemon must be configured to only use Message Authentication Codes (MACs) employing FIPS 140-2 approved cryptographic hash algorithms.

From Canonical Ubuntu 16.04 Security Technical Implementation Guide

Part of SRG-OS-000250-GPOS-00093

Associated with: CCI-001453 CCI-002890 CCI-003123

SV-90511r2_rule The SSH daemon must be configured to only use Message Authentication Codes (MACs) employing FIPS 140-2 approved cryptographic hash algorithms.

Vulnerability 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.Satisfies: SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174

Check content

Verify the SSH daemon is configured to only use Message Authentication Codes (MACs) that employ FIPS 140-2 approved ciphers. Check that the SSH daemon is configured to only use MACs that employ FIPS 140-2 approved ciphers with the following command: # sudo grep -i macs /etc/ssh/sshd_config MACs hmac-sha2-256,hmac-sha2-512 If any ciphers other than "hmac-sha2-256" or "hmac-sha2-512" are listed, or the retuned line is commented out, this is a finding.

Fix text

Configure the Ubuntu operating system to allow the SSH daemon to only use Message Authentication Codes (MACs) that employ FIPS 140-2 approved ciphers. Edit the "/etc/ssh/sshd_config" file to uncomment or add the line for the "MACs" keyword and set its value to "hmac-sha2-256" and/or "hmac-sha2-512": MACs hmac-sha2-256,hmac-sha2-512 The SSH daemon must be restarted for the changes to take effect. To restart the SSH daemon, run the following command: # sudo systemctl restart sshd.service

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