Vulnerability Discussion

Without the use of multifactor authentication, the ease of access to privileged functions is greatly increased. Multifactor authentication requires using two or more factors to achieve authentication. A privileged account is defined as an information system account with authorizations of a privileged user. A DOD common access card (CAC) with DOD-approved PKI is an example of multifactor authentication.

OpenSSH uses the first occurrence of a keyword it sees, and drop-in files are read in lexicographical order at the start of the configuration. Red Hat recommends using drop-in files rather than changing base configuration files.

Satisfies: SRG-OS-000105-GPOS-00052, SRG-OS-000106-GPOS-00053, SRG-OS-000107-GPOS-00054, SRG-OS-000108-GPOS-00055

Check

Note: If the system administrator demonstrates the use of an approved alternate multifactor authentication method, this requirement is not applicable.

Verify RHEL 10 SSH daemons accept public key encryption with the following command:

$ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*pubkeyauthentication'
/etc/ssh/sshd_config.d/10-stig.conf:PubkeyAuthentication yes

Verify the runtime setting with the following command:

$ sudo sshd -T | grep -i pubkeyauthentication
pubkeyauthentication yes

If the "PubkeyAuthentication" keyword is not set to "yes" in a drop-in that lexicographically precedes 50-redhat.conf, or if no output is returned, this is a finding.

Fix

Configure RHEL 10 to accept public key authentication.

In "/etc/ssh/sshd_config.d", create a drop file that will lexicographically precede 50-redhat.conf and add the following line:

PubkeyAuthentication yes

Restart the SSH daemon with the following command for the settings to take effect:

$ sudo systemctl restart sshd.service