Ubuntu 22.04 LTS must configure the SSH daemon to use FIPS 140-3-approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-260531	UBTU-22-255050	SV-260531r953406_rule		Medium

Description
Without cryptographic integrity protections, information can be altered by unauthorized users without detection. Remote access (e.g., RDP) 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. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. Encrypting information for transmission protects information from unauthorized disclosure and modification. Cryptographic mechanisms implemented to protect information integrity include, for example, cryptographic hash functions which have common application in digital signatures, checksums, and message authentication codes. 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. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000394-GPOS-00174, SRG-OS-000424-GPOS-00188

Description

Without cryptographic integrity protections, information can be altered by unauthorized users without detection. Remote access (e.g., RDP) 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. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. Encrypting information for transmission protects information from unauthorized disclosure and modification. Cryptographic mechanisms implemented to protect information integrity include, for example, cryptographic hash functions which have common application in digital signatures, checksums, and message authentication codes. 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. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000394-GPOS-00174, SRG-OS-000424-GPOS-00188

STIG	Date
Canonical Ubuntu 22.04 LTS Security Technical Implementation Guide	2024-03-21

Details

Check Text ( C-64260r953404_chk )
Verify the SSH server is configured to only implement FIPS-approved ciphers with the following command: $ sudo /usr/sbin/sshd -dd 2>&1 \| awk '/filename/ {print $4}' \| tr -d '\r' \| tr '\n' ' ' \| xargs sudo grep -iH 'ciphers' /etc/ssh/sshd_config:Ciphers aes256-ctr,aes256-gcm@openssh.com,aes192-ctr,aes128-ctr,aes128-gcm@openssh.com If "Ciphers" does not contain only the ciphers "aes256-ctr,aes256-gcm@openssh.com,aes192-ctr,aes128-ctr,aes128-gcm@openssh.com" in exact order, is commented out, is missing, or conflicting results are returned, this is a finding.

Check Text ( C-64260r953404_chk )

Verify the SSH server is configured to only implement FIPS-approved ciphers with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH 'ciphers'
/etc/ssh/sshd_config:Ciphers aes256-ctr,aes256-gcm@openssh.com,aes192-ctr,aes128-ctr,aes128-gcm@openssh.com

If "Ciphers" does not contain only the ciphers "aes256-ctr,aes256-gcm@openssh.com,aes192-ctr,aes128-ctr,aes128-gcm@openssh.com" in exact order, is commented out, is missing, or conflicting results are returned, this is a finding.

Fix Text (F-64168r953405_fix)
Configure the SSH server to only implement FIPS-approved ciphers. Add or modify the following line in the "/etc/ssh/sshd_config" file: Ciphers aes256-ctr,aes256-gcm@openssh.com,aes192-ctr,aes128-ctr,aes128-gcm@openssh.com Restart the SSH server for the changes to take effect: $ sudo systemctl restart sshd.service