Guide to the Secure Configuration of Red Hat Enterprise Linux 9
Rules, Groups, and Values defined within the XCCDF Benchmark
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Kerberos
The Kerberos protocol is used for authentication across non-secure network. Authentication can happen between various types of principals -- users,...Group -
Remove the Kerberos Server Package
The <code>krb5-server</code> package should be removed if not in use. Is this system the Kerberos server? If not, remove the package. The <code>krb...Rule Medium Severity -
Disable Kerberos by removing host keytab
Kerberos is not an approved key distribution method for Common Criteria. To prevent using Kerberos by system daemons, remove the Kerberos keytab fi...Rule Medium Severity -
LDAP
LDAP is a popular directory service, that is, a standardized way of looking up information from a central database. Red Hat Enterprise Linux 9 incl...Group -
Configure OpenLDAP Clients
This section provides information on which security settings are important to configure in OpenLDAP clients by manually editing the appropriate con...Group -
Ensure LDAP client is not installed
The Lightweight Directory Access Protocol (LDAP) is a service that provides a method for looking up information from a central database. The <code>...Rule Low Severity -
Configure OpenLDAP Server
This section details some security-relevant settings for an OpenLDAP server.Group -
Uninstall openldap-servers Package
The openldap-servers package is not installed by default on a Red Hat Enterprise Linux 9 system. It is needed only by the OpenLDAP server, not by t...Rule Low Severity -
Disable LDAP Server (slapd)
The Lightweight Directory Access Protocol (LDAP) is a service that provides a method for looking up information from a central database.Rule Medium Severity -
Install and Protect LDAP Certificate Files
Create the PKI directory for LDAP certificates if it does not already exist: <pre>$ sudo mkdir /etc/pki/tls/ldap $ sudo chown root:root /etc/pki/tl...Group -
Disable Postfix Network Listening
Edit the file <code>/etc/postfix/main.cf</code> to ensure that only the following <code>inet_interfaces</code> line appears: <pre>inet_interfaces =...Rule Medium Severity -
Mail Server Software
Mail servers are used to send and receive email over the network. Mail is a very common service, and Mail Transfer Agents (MTAs) are obvious target...Group -
The Postfix package is installed
A mail server is required for sending emails. The <code>postfix</code> package can be installed with the following command: <pre> $ sudo dnf instal...Rule Medium Severity -
Uninstall Sendmail Package
Sendmail is not the default mail transfer agent and is not installed by default. The <code>sendmail</code> package can be removed with the followin...Rule Medium Severity -
Enable Postfix Service
The Postfix mail transfer agent is used for local mail delivery within the system. The default configuration only listens for connections to the de...Rule Unknown Severity -
Ensure Mail Transfer Agent is not Listening on any non-loopback Address
Mail Transfer Agents (MTA), such as sendmail and Postfix, are used to listen for incoming mail and transfer the messages to the appropriate user or...Rule Medium Severity -
Configure SMTP For Mail Clients
This section discusses settings for Postfix in a submission-only e-mail configuration.Group -
Postfix Network Interfaces
The setting for inet_interfaces in /etc/postfix/main.cfValue -
Postfix relayhost
Specify the host all outbound email should be routed into.Value -
Postfix Root Mail Alias
Specify an email address (string) for a root mail alias.Value -
Configure System to Forward All Mail For The Root Account
Make sure that mails delivered to root user are forwarded to a monitored email address. Make sure that the address <xccdf-1.2:sub idref="xccdf_org....Rule Medium Severity -
Configure System to Forward All Mail From Postmaster to The Root Account
Verify the administrators are notified in the event of an audit processing failure. Check that the "/etc/aliases" file has a defined value for "roo...Rule Medium Severity -
Configure System to Forward All Mail through a specific host
Set up a relay host that will act as a gateway for all outbound email. Edit the file <code>/etc/postfix/main.cf</code> to ensure that only the foll...Rule Medium Severity -
Configure SSL Certificates for Use with SMTP AUTH
If SMTP AUTH is to be used, the use of SSL to protect credentials in transit is strongly recommended. There are also configurations for which it ma...Group -
Ensure Security of Postfix SSL Certificate
Create the PKI directory for mail certificates, if it does not already exist: <pre>$ sudo mkdir /etc/pki/tls/mail $ sudo chown root:root /etc/pki/t...Group -
Configure Postfix if Necessary
Postfix stores its configuration files in the directory /etc/postfix by default. The primary configuration file is/etc/postfix/main.cf.Group -
Configure Postfix Resource Usage to Limit Denial of Service Attacks
Edit <code>/etc/postfix/main.cf</code>. Edit the following lines to configure the amount of system resources Postfix can consume: <pre>default_proc...Group -
Control Mail Relaying
Postfix's mail relay controls are implemented with the help of the smtpd recipient restrictions option, which controls the restrictions placed on t...Group -
Prevent Unrestricted Mail Relaying
Modify the <pre>/etc/postfix/main.cf</pre> file to restrict client connections to the local network with the following command: <pre>$ sudo postcon...Rule Medium Severity -
Enact SMTP Recipient Restrictions
To configure Postfix to restrict addresses to which it will send mail, see: <a href="http://www.postfix.org/SMTPD_ACCESS_README.html#danger">h...Group -
Enact SMTP Relay Restrictions
To configure Postfix to restrict addresses to which it will send mail, see: <a href="http://www.postfix.org/SMTPD_ACCESS_README.html#danger">h...Group -
Use TLS for SMTP AUTH
Postfix provides options to use TLS for certificate-based authentication and encrypted sessions. An encrypted session protects the information that...Group -
Configure Trusted Networks and Hosts
Edit <code>/etc/postfix/main.cf</code>, and configure the contents of the <code>mynetworks</code> variable in one of the following ways: <ul> <li>I...Group -
Require SMTP AUTH Before Relaying from Untrusted Clients
SMTP authentication allows remote clients to relay mail safely by requiring them to authenticate before submitting mail. Postfix's SMTP AUTH uses a...Group -
NFS and RPC
The Network File System is a popular distributed filesystem for the Unix environment, and is very widely deployed. This section discusses the circ...Group -
Uninstall nfs-utils Package
Thenfs-utilspackage can be removed with the following command:$ sudo dnf erase nfs-utils
Rule Low Severity -
Disable All NFS Services if Possible
If there is not a reason for the system to operate as either an NFS client or an NFS server, follow all instructions in this section to disable sub...Group -
Disable netfs if Possible
To determine if any network filesystems handled by netfs are currently mounted on the system execute the following command: <pre>$ mount -t nfs,nfs...Group -
Disable Network File Systems (netfs)
The netfs script manages the boot-time mounting of several types of networked filesystems, of which NFS and Samba are the most common. If these fil...Rule Unknown Severity -
Disable Services Used Only by NFS
If NFS is not needed, disable the NFS client daemons nfslock, rpcgssd, and rpcidmapd. <br><br> All of these daemons run with elevated privileges, a...Group -
Uninstall rpcbind Package
The rpcbind utility maps RPC services to the ports on which they listen. RPC processes notify rpcbind when they start, registering the ports they a...Rule Low Severity -
Disable rpcbind Service
The rpcbind utility maps RPC services to the ports on which they listen. RPC processes notify rpcbind when they start, registering the ports they a...Rule Low Severity -
Configure All Systems which Use NFS
The steps in this section are appropriate for all systems which run NFS, whether they operate as clients or as servers.Group -
Make Each System a Client or a Server, not Both
If NFS must be used, it should be deployed in the simplest configuration possible to avoid maintainability problems which may lead to unnecessary s...Group -
Configure NFS Services to Use Fixed Ports (NFSv3 and NFSv2)
Firewalling should be done at each host and at the border firewalls to protect the NFS daemons from remote access, since NFS servers should never b...Group -
Disable Network File System (nfs)
The Network File System (NFS) service allows remote hosts to mount and interact with shared filesystems on the local system. If the local system is...Rule Unknown Severity -
Mount Remote Filesystems with Restrictive Options
Edit the file <code>/etc/fstab</code>. For each filesystem whose type (column 3) is <code>nfs</code> or <code>nfs4</code>, add the text <code>,node...Group -
Mount Remote Filesystems with Kerberos Security
Add the <code>sec=krb5:krb5i:krb5p</code> option to the fourth column of <code>/etc/fstab</code> for the line which controls mounting of any NFS mo...Rule Medium Severity -
Mount Remote Filesystems with nodev
Add thenodevoption to the fourth column of/etc/fstabfor the line which controls mounting of any NFS mounts.Rule Medium Severity -
Mount Remote Filesystems with noexec
Add thenoexecoption to the fourth column of/etc/fstabfor the line which controls mounting of any NFS mounts.Rule Medium Severity
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