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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-75829	UBTU-16-030230	SV-90509r2_rule		Medium

Description
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.

Description

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.

STIG	Date
Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide	2018-07-18

Details

Check Text ( C-75517r2_chk )
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.

Check Text ( C-75517r2_chk )

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 (F-82459r2_fix)
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

Fix Text (F-82459r2_fix)

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