NIST National Checklist Program Security Guide
Rules and Groups employed by this XCCDF Profile
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Chat/Messaging Services
The talk software makes it possible for users to send and receive messages across systems through a terminal session.Group -
Uninstall talk-server Package
Thetalk-server
package can be removed with the following command:$ sudo yum erase talk-server
Rule Medium Severity -
Uninstall talk Package
The <code>talk</code> package contains the client program for the Internet talk protocol, which allows the user to chat with other users on different systems. Talk is a communication program which ...Rule Medium Severity -
Telnet
The telnet protocol does not provide confidentiality or integrity for information transmitted on the network. This includes authentication information such as passwords. Organizations which use tel...Group -
Uninstall telnet-server Package
Thetelnet-server
package can be removed with the following command:$ sudo yum erase telnet-server
Rule High Severity -
Remove telnet Clients
The telnet client allows users to start connections to other systems via the telnet protocol.Rule Low Severity -
Disable telnet Service
Make sure that the activation of the <code>telnet</code> service on system boot is disabled. The <code>telnet</code> socket can be disabled with the following command: <pre>$ sudo systemctl mask -...Rule High Severity -
Network Routing
A router is a very desirable target for a potential adversary because they fulfill a variety of infrastructure networking roles such as access to network segments, gateways to other networks, filt...Group -
Disable Quagga if Possible
If Quagga was installed and activated, but the system does not need to act as a router, then it should be disabled and removed.Group -
Disable Quagga Service
Thezebra
service can be disabled with the following command:$ sudo systemctl mask --now zebra.service
Rule Medium Severity -
SSH Server
The SSH protocol is recommended for remote login and remote file transfer. SSH provides confidentiality and integrity for data exchanged between two systems, as well as server authentication, throu...Group -
Enable the OpenSSH Service
The SSH server service, sshd, is commonly needed. Thesshd
service can be enabled with the following command:$ sudo systemctl enable sshd.service
Rule Medium Severity -
Verify Permissions on SSH Server Private *_key Key Files
SSH server private keys - files that match the <code>/etc/ssh/*_key</code> glob, have to have restricted permissions. If those files are owned by the <code>root</code> user and the <code>root</code...Rule Medium Severity -
Verify Permissions on SSH Server Public *.pub Key Files
To properly set the permissions of/etc/ssh/*.pub
, run the command:$ sudo chmod 0644 /etc/ssh/*.pub
Rule Medium Severity -
Configure OpenSSH Server if Necessary
If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file <code>/etc/ssh/sshd_config</code>. The following recommendations can be app...Group -
Set SSH Client Alive Count Max to zero
The SSH server sends at most <code>ClientAliveCountMax</code> messages during a SSH session and waits for a response from the SSH client. The option <code>ClientAliveInterval</code> configures time...Rule Medium Severity -
Set SSH Client Alive Interval
SSH allows administrators to set a network responsiveness timeout interval. After this interval has passed, the unresponsive client will be automatically logged out. <br> <br> To set this t...Rule Medium Severity -
Disable Host-Based Authentication
SSH's cryptographic host-based authentication is more secure than <code>.rhosts</code> authentication. However, it is not recommended that hosts unilaterally trust one another, even within an organ...Rule Medium Severity -
Enable SSH Server firewalld Firewall Exception
If the SSH server is in use, inbound connections to SSH's port should be allowed to permit remote access through SSH. In more restrictive firewalld settings, the SSH port should be added to the pro...Rule Medium Severity -
Allow Only SSH Protocol 2
Only SSH protocol version 2 connections should be permitted. The default setting in <code>/etc/ssh/sshd_config</code> is correct, and can be verified by ensuring that the following line appears: <p...Rule High Severity -
Disable Compression Or Set Compression to delayed
Compression is useful for slow network connections over long distances but can cause performance issues on local LANs. If use of compression is required, it should be enabled only after a user has ...Rule Medium Severity -
Disable SSH Access via Empty Passwords
Disallow SSH login with empty passwords. The default SSH configuration disables logins with empty passwords. The appropriate configuration is used if no value is set for <code>PermitEmptyPasswords<...Rule High Severity -
Disable GSSAPI Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like GSSAPI. <br> The default SSH configuration disallows authentications based on GSSAPI. The appropriate c...Rule Medium Severity -
Disable Kerberos Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like Kerberos. <br> The default SSH configuration disallows authentication validation through Kerberos. The ...Rule Medium Severity -
Disable SSH Support for Rhosts RSA Authentication
SSH can allow authentication through the obsolete rsh command through the use of the authenticating user's SSH keys. This should be disabled. <br> <br> To ensure this behavior is disabled, ...Rule Medium Severity -
Disable SSH Root Login
The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>Pe...Rule Medium Severity -
Do Not Allow SSH Environment Options
Ensure that users are not able to override environment variables of the SSH daemon. <br> The default SSH configuration disables environment processing. The appropriate configuration is used if no v...Rule Medium Severity -
Enable Use of Strict Mode Checking
SSHs <code>StrictModes</code> option checks file and ownership permissions in the user's home directory <code>.ssh</code> folder before accepting login. If world- writable permissions are found, lo...Rule Medium Severity -
Enable SSH Warning Banner
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>Banner /etc/issue</pre> Another section c...Rule Medium Severity -
Enable Encrypted X11 Forwarding
By default, remote X11 connections are not encrypted when initiated by users. SSH has the capability to encrypt remote X11 connections when SSH's <code>X11Forwarding</code> option is enabled. <br> ...Rule High Severity -
Use Only FIPS 140-2 Validated Ciphers
Limit the ciphers to those algorithms which are FIPS-approved. Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode. The following line in <code>/etc/ssh/sshd_config</code> de...Rule Medium Severity -
Use Only FIPS 140-2 Validated MACs
Limit the MACs to those hash algorithms which are FIPS-approved. The following line in <code>/etc/ssh/sshd_config</code> demonstrates use of FIPS-approved MACs: <pre>MACs hmac-sha2-512,hmac-sha2-2...Rule Medium Severity -
Enable Use of Privilege Separation
When enabled, SSH will create an unprivileged child process that has the privilege of the authenticated user. To enable privilege separation in SSH, add or correct the following line in the <code>/...Rule Medium Severity -
System Security Services Daemon
The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red Hat's IdM, Microsoft's AD, openLDAP, MIT Kerberos, ...Group -
Enable Smartcards in SSSD
SSSD should be configured to authenticate access to the system using smart cards. To enable smart cards in SSSD, set <code>pam_cert_auth</code> to <code>True</code> under the <code>[pam]</code> sec...Rule Medium Severity -
Configure SSSD to Expire SSH Known Hosts
SSSD should be configured to expire keys from known SSH hosts after <code><xccdf-1.2:sub idref="xccdf_org.ssgproject.content_value_var_sssd_ssh_known_hosts_timeout" use="legacy"></xccdf-1.2:sub></c...Rule Medium Severity
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