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Guide to the Secure Configuration of Red Hat Enterprise Linux 7

Rules, Groups, and Values defined within the XCCDF Benchmark

  • Enable SSL Support

    SSL should be used to encrypt network traffic between the Dovecot server and its clients. Users must authenticate to the Dovecot server in order to read their mail, and passwords should never be ...
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  • Configure Dovecot to Use the SSL Certificate file

    This option tells Dovecot where to find the mail server's SSL Certificate. <br><br> Edit <code>/etc/dovecot/conf.d/10-ssl.conf</code> and add or correct the following line (<i>note: the path below ...
    Rule Unknown Severity
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  • Configure Dovecot to Use the SSL Key file

    This option tells Dovecot where to find the mail server's SSL Key. <br><br> Edit <code>/etc/dovecot/conf.d/10-ssl.conf</code> and add or correct the following line (<i>note: the path below is the d...
    Rule Unknown Severity
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  • Enable the SSL flag in /etc/dovecot.conf

    To allow clients to make encrypted connections the <code>ssl</code> flag in Dovecot's configuration file needs to be set to <code>yes</code>. <br><br> Edit <code>/etc/dovecot/conf.d/10-ssl.conf</co...
    Rule Unknown Severity
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  • Support Only the Necessary Protocols

    Dovecot supports the IMAP and POP3 protocols, as well as SSL-protected versions of those protocols. Configure the Dovecot server to support only the protocols needed by your site. Edit <code>/etc...
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  • Disable Cyrus IMAP

    If the system does not need to operate as an IMAP or POP3 server, the Cyrus IMAP software should be removed.
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  • Disable Dovecot

    If the system does not need to operate as an IMAP or POP3 server, the dovecot software should be disabled and removed.
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  • Uninstall dovecot Package

    The dovecot package can be removed with the following command: 
    $ sudo yum erase dovecot
    Rule Unknown Severity
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  • Disable Dovecot Service

    The dovecot service can be disabled with the following command: 
    $ sudo systemctl mask --now dovecot.service
    Rule Unknown Severity
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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, service, or hosts. Their identity and encryption ...
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  • 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>krb5-server</code> package can be removed with the fo...
    Rule Medium Severity
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  • 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 files, especially /etc/krb5.keytab.
    Rule Medium Severity
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  • LDAP

    LDAP is a popular directory service, that is, a standardized way of looking up information from a central database. Red Hat Enterprise Linux 7 includes software that enables a system to act as both...
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  • Configure OpenLDAP Clients

    This section provides information on which security settings are important to configure in OpenLDAP clients by manually editing the appropriate configuration files. Red Hat Enterprise Linux 7 prov...
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  • 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>openldap-clients</code> package can be removed wit...
    Rule Low Severity
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  • Enable the LDAP Client For Use in Authconfig

    To determine if LDAP is being used for authentication, use the following command: <pre>$ sudo grep -i useldapauth /etc/sysconfig/authconfig</pre> <br><br> If <code>USELDAPAUTH=yes</code>, then LDAP...
    Rule Medium Severity
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  • Configure LDAP Client to Use TLS For All Transactions

    This check verifies cryptography has been implemented to protect the integrity of remote LDAP authentication sessions. <br><br> To determine if LDAP is being used for authentication, use the follow...
    Rule Medium Severity
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  • Configure Certificate Directives for LDAP Use of TLS

    Ensure a copy of a trusted CA certificate has been placed in the file <code>/etc/pki/tls/CA/cacert.pem</code>. Configure LDAP to enforce TLS use and to trust certificates signed by that CA. First, ...
    Rule Medium Severity
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  • Configure OpenLDAP Server

    This section details some security-relevant settings for an OpenLDAP server. Installation and configuration of OpenLDAP on Red Hat Enterprise Linux 7 is available at: <a href="https://access....
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  • Uninstall openldap-servers Package

    The openldap-servers package is not installed by default on a Red Hat Enterprise Linux 7 system. It is needed only by the OpenLDAP server, not by the clients which use LDAP for authentication. If t...
    Rule Low Severity
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  • 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/tls/ldap $ sudo chmod 755 /etc/pki/tls/ldap</pre> Us...
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  • 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 targets of network attack. Ensure that systems are not r...
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  • The mailx Package Is Installed

    A mail server is required for sending emails. The mailx package can be installed with the following command: 
    $ sudo yum install mailx
    Rule Medium Severity
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  • The Postfix package is installed

    A mail server is required for sending emails. The postfix package can be installed with the following command: 
    $ sudo yum install postfix
    Rule Medium Severity
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  • Uninstall Sendmail Package

    Sendmail is not the default mail transfer agent and is not installed by default. The sendmail package can be removed with the following command: 
    $ sudo yum erase sendmail
    Rule Medium Severity
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  • 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 mail server. If the system is not intended to be ...
    Rule Medium Severity
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  • Configure SMTP For Mail Clients

    This section discusses settings for Postfix in a submission-only e-mail configuration.
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  • Postfix Network Interfaces

    The setting for inet_interfaces in /etc/postfix/main.cf
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  • Postfix relayhost

    Specify the host all outbound email should be routed into.
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  • Postfix Root Mail Alias

    Specify an email address (string) for a root mail alias.
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  • 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.ssgproject.content_value_var_postfix_root_mail_ali...
    Rule Medium Severity
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  • 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 "root". <pre>$ sudo grep "postmaster:\s*root$" /etc/al...
    Rule Medium Severity
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  • 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 following <code>relayhost</code> line appears: <pre>re...
    Rule Medium Severity
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  • 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 = <xccdf-1.2:sub idref="xccdf_org.ssgproject.conten...
    Rule Medium Severity
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  • Configure Operating System to Protect Mail Server

    The guidance in this section is appropriate for any host which is operating as a site MTA, whether the mail server runs using Sendmail, Postfix, or some other software.
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  • 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 may be desirable to encrypt all mail in transit from...
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  • 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/tls/mail $ sudo chmod 755 /etc/pki/tls/mail</pre> U...
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  • 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.
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  • Configure SMTP Greeting Banner

    Edit /etc/postfix/main.cf, and add or correct the following line, substituting some other wording for the banner information if you prefer: 
    smtpd_banner = $myhostname ESMTP
    Rule Low Severity
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  • 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_process_limit = 100 smtpd_client_connection_count_limi...
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  • 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 the SMTP dialogue once the sender and recipient env...
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  • 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 postconf -e 'smtpd_client_restrictions = permit_mynetwork...
    Rule Medium Severity
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  • 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">http://www.postfix.org/SMTPD_ACCESS_README.html#dan...
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  • 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">http://www.postfix.org/SMTPD_ACCESS_README.html#dan...
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  • 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 is transmitted with SMTP mail or with SASL authen...
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  • 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>If any system in the subnet containing the MTA may ...
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  • 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 an authentication library called SASL, which is not...
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  • 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 circumstances under which it is possible to disable NF...
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  • Uninstall nfs-utils Package

    The nfs-utils package can be removed with the following command: 
    $ sudo yum erase nfs-utils
    Rule Low Severity
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  • 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 subsystems required by NFS.
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