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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-215125	UBTU-16-030240	SV-215125r610931_rule		Medium

Description
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

Description

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

STIG	Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide	2020-12-09

Details

Check Text ( C-16324r608742_chk )
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-sha2-512,hmac-sha2-256 If any ciphers other than "hmac-sha2-512" or "hmac-sha2-256" are listed, the order differs from the example above, or the returned line is commented out, this is a finding.

Check Text ( C-16324r608742_chk )

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-sha2-512,hmac-sha2-256

If any ciphers other than "hmac-sha2-512" or "hmac-sha2-256" are listed, the order differs from the example above, or the returned line is commented out, this is a finding.

Fix Text (F-16322r608743_fix)
Configure the Ubuntu operating system to allow the SSH daemon to only use Message Authentication Codes (MACs) that employ FIPS 140-2 approved ciphers. Add the following line (or modify the line to have the required value) to the "/etc/ssh/sshd_config" file (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor): MACs hmac-sha2-512,hmac-sha2-256 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

Fix Text (F-16322r608743_fix)

Configure the Ubuntu operating system to allow the SSH daemon to only use Message Authentication Codes (MACs) that employ FIPS 140-2 approved ciphers.

Add the following line (or modify the line to have the required value) to the "/etc/ssh/sshd_config" file (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor):

MACs hmac-sha2-512,hmac-sha2-256

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