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V-255899

CAT II (Medium)

The Oracle Linux operating system SSH server must be configured to use only FIPS-validated key exchange algorithms.

Rule ID

SV-255899r958408_rule

STIG

Oracle Linux 7 Security Technical Implementation Guide

Version

V3R5

CCIs

CCI-001453

Discussion

The use of FIPS-validated cryptographic algorithms is enforced by enabling kernel FIPS mode. In the event that kernel FIPS mode is disabled, the use of nonvalidated cryptographic algorithms will be permitted systemwide. The SSH server configuration must manually define only FIPS-validated key exchange algorithms to prevent the use of nonvalidated algorithms.

Check Content

Verify that the SSH server is configured to use only FIPS-validated key exchange algorithms:

     $ sudo grep -i kexalgorithms /etc/ssh/sshd_config
     KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256
 
If "KexAlgorithms" is not configured, is commented out, or does not contain only the algorithms "ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256" in exact order, this is a finding.

Fix Text

Configure the SSH server to use only FIPS-validated key exchange algorithms by adding or modifying the following line in "/etc/ssh/sshd_config":

     KexAlgorithms ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256

Restart the "sshd" service for changes to take effect:

     $ sudo systemctl restart sshd