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

From Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide

Part of SRG-OS-000033-GPOS-00014

Associated with: CCI-000068

SV-90509r2_rule The Ubuntu operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.

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, 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

Pro Tips

Lavender hyperlinks in small type off to the right (of CSS class id, if you view the page source) point to globally unique URIs for each document and item. Copy the link location and paste anywhere you need to talk unambiguously about these things.

You can obtain data about documents and items in other formats. Simply provide an HTTP header Accept: text/turtle or Accept: application/rdf+xml.

Powered by sagemincer