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-219561r603343_rule		Medium

Description
Approved algorithms should impart some level of confidence in their implementation. These are also required for compliance. 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.

STIG	Date
Oracle Linux 6 Security Technical Implementation Guide	2021-03-01

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.