The macOS system must implement approved ciphers to protect the confidentiality of SSH connections.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-230767	APPL-11-000054	SV-230767r599842_rule		Medium

Description
Unapproved mechanisms for authentication to the cryptographic module are not verified, and therefore cannot be relied upon to provide confidentiality or integrity, resulting in the compromise of DoD data. Operating systems using encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules. The implementation of OpenSSH that is included with macOS does not use a FIPS 140-2 validated cryptographic module. While the listed ciphers are FIPS 140-2 approved algorithms, the module implementing them has not been validated. 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-000120-GPOS-00061, SRG-OS-000125-GPOS-00065, SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174

Description

Unapproved mechanisms for authentication to the cryptographic module are not verified, and therefore cannot be relied upon to provide confidentiality or integrity, resulting in the compromise of DoD data. Operating systems using encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules. The implementation of OpenSSH that is included with macOS does not use a FIPS 140-2 validated cryptographic module. While the listed ciphers are FIPS 140-2 approved algorithms, the module implementing them has not been validated. 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-000120-GPOS-00061, SRG-OS-000125-GPOS-00065, SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, SRG-OS-000394-GPOS-00174

STIG	Date
Apple macOS 11 (Big Sur) Security Technical Implementation Guide	2020-11-27

Details

Check Text ( C-33712r591423_chk )
If SSH is not being used, this is Not Applicable. Inspect the "Ciphers" configuration with the following command: Note: The location of the "sshd_config" file may vary if a different daemon is in use. # /usr/bin/grep "^Ciphers" /etc/ssh/sshd_config Ciphers aes256-ctr,aes192-ctr,aes128-ctr If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, or the "Ciphers" keyword is missing, this is a finding.

Check Text ( C-33712r591423_chk )

If SSH is not being used, this is Not Applicable.

Inspect the "Ciphers" configuration with the following command:
Note: The location of the "sshd_config" file may vary if a different daemon is in use.

# /usr/bin/grep "^Ciphers" /etc/ssh/sshd_config

Ciphers aes256-ctr,aes192-ctr,aes128-ctr

If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, or the "Ciphers" keyword is missing, this is a finding.

Fix Text (F-33685r592244_fix)
Configure SSH to use secure cryptographic algorithms. To ensure that "Ciphers" set correctly, run the following command: /usr/bin/sudo /usr/bin/grep -q '^Ciphers' /etc/ssh/sshd_config && /usr/bin/sudo /usr/bin/sed -i.bak 's/^Ciphers./Ciphers aes256-ctr,aes192-ctr,aes128-ctr/' /etc/ssh/sshd_config \|\| /usr/bin/sudo /usr/bin/sed -i.bak '/.Ciphers and keying.*/a\'$'\n''Ciphers aes256-ctr,aes192-ctr,aes128-ctr'$'\n' /etc/ssh/sshd_config The SSH service must be restarted for changes to take effect.

Fix Text (F-33685r592244_fix)

Configure SSH to use secure cryptographic algorithms.

To ensure that "Ciphers" set correctly, run the following command:

/usr/bin/sudo /usr/bin/grep -q '^Ciphers' /etc/ssh/sshd_config && /usr/bin/sudo /usr/bin/sed -i.bak 's/^Ciphers.*/Ciphers aes256-ctr,aes192-ctr,aes128-ctr/' /etc/ssh/sshd_config || /usr/bin/sudo /usr/bin/sed -i.bak '/.*Ciphers and keying.*/a\'$'\n''Ciphers aes256-ctr,aes192-ctr,aes128-ctr'$'\n' /etc/ssh/sshd_config

The SSH service must be restarted for changes to take effect.