The macOS system must implement approved Key Exchange Algorithms within the SSH client configuration.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257775	APPL-12-000059	SV-257775r922870_rule		High

Description
Operating systems using encryption are required to use FIPS-compliant mechanisms for authenticating to macOS. For OpenSSH to utilize the Apple Corecrypto FIPS-validated algorithms, a specific configuration is required to leverage the shim implemented by macOS to bypass the non-FIPS validated LibreSSL crypto module packaged with OpenSSH. Information regarding this configuration can be found in the manual page "apple_ssh_and_fips". 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-00176

Description

Operating systems using encryption are required to use FIPS-compliant mechanisms for authenticating to macOS. For OpenSSH to utilize the Apple Corecrypto FIPS-validated algorithms, a specific configuration is required to leverage the shim implemented by macOS to bypass the non-FIPS validated LibreSSL crypto module packaged with OpenSSH. Information regarding this configuration can be found in the manual page "apple_ssh_and_fips". 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-00176

STIG	Date
Apple macOS 12 (Monterey) Security Technical Implementation Guide	2023-08-28

Details

Check Text ( C-61516r922868_chk )
Verify the macOS system is configured to use approved SSH Key Exchange Algorithms within the SSH client configuration with the following command: /usr/bin/sudo /usr/bin/grep -ir "kexalgorithms" /etc/ssh/ssh_config* /etc/ssh/ssh_config.d/fips_ssh_config:KexAlgorithms ecdh-sha2-nistp256 If any algorithms other than "ecdh-sha2-nistp256" are listed, or the "kexalgorithms" keyword is missing, this is a finding.

Check Text ( C-61516r922868_chk )

Verify the macOS system is configured to use approved SSH Key Exchange Algorithms within the SSH client configuration with the following command:

/usr/bin/sudo /usr/bin/grep -ir "kexalgorithms" /etc/ssh/ssh_config*

/etc/ssh/ssh_config.d/fips_ssh_config:KexAlgorithms ecdh-sha2-nistp256

If any algorithms other than "ecdh-sha2-nistp256" are listed, or the "kexalgorithms" keyword is missing, this is a finding.

Fix Text (F-61440r922869_fix)
Configure the macOS system to use approved SSH Key Exchange Algorithms by creating a plain text file in the /private/etc/ssh/ssh_config.d/ directory containing the following: KexAlgorithms ecdh-sha2-nistp256 The SSH service must be restarted for changes to take effect.