The Oracle Linux 6 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-219561	OL6-00-000243	SV-219561r744067_rule		Medium

Description
Approved algorithms should impart some level of confidence in their implementation. These are also required for compliance. The system will attempt to use the first cipher 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 cipher available to secure the SSH connection.

STIG	Date
Oracle Linux 6 Security Technical Implementation Guide	2021-06-14

Details

Check Text ( C-21286r622245_chk )
Only FIPS-approved ciphers should be used. To verify that only FIPS-approved ciphers are in use, run the following command: # grep -i Ciphers /etc/ssh/sshd_config Ciphers aes256-ctr,aes192-ctr,aes128-ctr If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, the "Ciphers" keyword is missing, or the returned line is commented out, this is a finding.

Check Text ( C-21286r622245_chk )

Only FIPS-approved ciphers should be used. To verify that only FIPS-approved ciphers are in use, run the following command:

# grep -i Ciphers /etc/ssh/sshd_config

Ciphers aes256-ctr,aes192-ctr,aes128-ctr

If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, the "Ciphers" keyword is missing, or the returned line is commented out, this is a finding.

Fix Text (F-21285r622246_fix)
Limit the ciphers to those algorithms which are FIPS-approved. The following line in "/etc/ssh/sshd_config" demonstrates use of FIPS-approved ciphers: Ciphers 256-ctr,aes192-ctr,aes128-ctr Note: The man page "sshd_config(5)" contains a list of supported ciphers.