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UBTU-24-100840 Ubuntu 24.04 LTS SSH server must be configured to use only FIPS 140-3 validated key exchange algorithms.

DISA STIG library V1R7
All changes in this version
first version loaded CAT II

Maps to AC-17(2) via CCI-000068

Title

Ubuntu 24.04 LTS SSH server must be configured to use only FIPS 140-3 validated key exchange algorithms.

Control

Verify that the SSH daemon is configured to use only FIPS-validated key exchange algorithms with the following command: $ sudo grep -ir kexalgorithms /etc/ssh/sshd_config* KexAlgorithms ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group14-sha256 If "KexAlgorithms" does not contain only the algorithms "ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group14-sha256", is commented out, or is missing, this is a finding.

Discussion

Without cryptographic integrity protections provided by FIPS-validated cryptographic algorithms, information can be viewed and altered by unauthorized users without detection. The system will attempt to use the first algorithm presented by the client that matches the server list.

Related controls

CCI-000068

Fix

Configure the SSH daemon to use only FIPS-validated key exchange algorithms by adding or modifying the following line in "/etc/ssh/sshd_config": KexAlgorithms ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group14-sha256 Restart the "sshd" service for changes to take effect: $ sudo systemctl restart sshd