SLEM 5 SSH daemon must be configured to only use Message Authentication Codes (MACs) employing FIPS 140-2/140-3 approved cryptographic hash algorithms.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-261335	SLEM-05-255050	SV-261335r996469_rule		High

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, 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. The system will attempt to use the first hash presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest hash available to secure the SSH connection.

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, 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. The system will attempt to use the first hash presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest hash available to secure the SSH connection.

STIG	Date
SUSE Linux Enterprise Micro (SLEM) 5 Security Technical Implementation Guide	2024-06-04

Details

Check Text ( C-65064r996468_chk )
Verify SLEM 5 SSH daemon is configured to only use MACs that employ FIPS 140-2/140-3 approved hashes with the following command: > sudo /usr/sbin/sshd -dd 2>&1 \| awk '/filename/ {print $4}' \| tr -d '\r' \| tr '\n' ' ' \| xargs sudo grep -iH '^\s*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, is commented out, missing, or conflicting results are returned, this is a finding.

Check Text ( C-65064r996468_chk )

Verify SLEM 5 SSH daemon is configured to only use MACs that employ FIPS 140-2/140-3 approved hashes with the following command:

> sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*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, is commented out, missing, or conflicting results are returned, this is a finding.

Fix Text (F-64972r995871_fix)
Configure SLEM 5 SSH daemon to only use MACs that employ FIPS 140-2/140-3 approved hashes. Add or modify the following line in the "/etc/ssh/sshd_config" file: MACs hmac-sha2-512,hmac-sha2-256