Title

The Ubuntu operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections. (Cat II impact)

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, non-organization-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 Content

Verify the SSH daemon is configured to only implement DoD-approved encryption. Check the SSH daemon's current configured ciphers by running the following command: # sudo grep -i ciphers /etc/ssh/sshd_config | grep -v '^#' Ciphers aes128-ctr,aes192-ctr,aes256-ctr If any ciphers other than "aes128-ctr", "aes192-ctr", or "aes256-ctr" are listed, the "Ciphers" keyword is missing, or the retuned line is commented out, this is a finding.

Fix Text

Configure the Ubuntu operating system to allow the SSH daemon to only implement DoD-approved encryption. Edit the SSH daemon configuration "/etc/ssh/sshd_config" and remove any ciphers not starting with "aes" and remove any ciphers ending with "cbc". If necessary, append the "Ciphers" line to the "/etc/ssh/sshd_config" document. Ciphers aes128-ctr,aes192-ctr,aes256-ctr 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

Additional Identifiers

Rule ID: SV-90509r3_rule

Vulnerability ID: V-75829

Group Title:

Expert Comments

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