Vulnerability Discussion

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session.

Remote access 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.

Encryption provides a means to secure the remote connection to prevent unauthorized access to the data traversing the remote access connection (e.g., RDP), thereby providing a degree of confidentiality. The encryption strength of a mechanism is selected based on the security categorization of the information.

Check

Verify Amazon Linux 2023 is configured so that the SSH server uses only ciphers employing FIPS 140-2/140-3 approved algorithms with the following command:

$ sudo grep -i ciphers /etc/crypto-policies/back-ends/opensshserver.config
Ciphers aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr

If the cipher entries in the "opensshserver.config" file have any ciphers other than "aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr", they are missing, or commented out, this is a finding.

Fix

Configure Amazon Linux 2023 SSH server to use only ciphers employing FIPS 140-2/140-3 approved algorithms by updating the "/etc/crypto-policies/back-ends/opensshserver.config" file with the following line:

Ciphers aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr

A reboot is required for the changes to take effect.