Guide to the Secure Configuration of Red Hat Enterprise Linux 8
Rules, Groups, and Values defined within the XCCDF Benchmark
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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 target...Group -
The mailx Package Is Installed
A mail server is required for sending emails. The <code>mailx</code> package can be installed with the following command: <pre> $ sudo yum install ...Rule Medium Severity -
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 yum 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 -
Disable RPC ID Mapping Service (rpcidmapd)
The rpcidmapd service is used to map user names and groups to UID and GID numbers on NFSv4 mounts. If NFS is not in use on the local system then th...Rule Unknown 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 -
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 -
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...Group -
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 SMTP Greeting Banner
Edit <code>/etc/postfix/main.cf</code>, and add or correct the following line, substituting some other wording for the banner information if you pr...Rule Low Severity -
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 -
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 -
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 yum 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 Network File System Lock Service (nfslock)
The Network File System Lock (nfslock) service starts the required remote procedure call (RPC) processes which allow clients to lock files on the s...Rule Unknown Severity -
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 -
Configure lockd to use static TCP port
Configure the <code>lockd</code> daemon to use a static TCP port as opposed to letting the RPC Bind service dynamically assign a port. Edit the fil...Rule Unknown Severity -
Configure lockd to use static UDP port
Configure the <code>lockd</code> daemon to use a static UDP port as opposed to letting the RPC Bind service dynamically assign a port. Edit the fil...Rule Unknown Severity -
Configure mountd to use static port
Configure the <code>mountd</code> daemon to use a static port as opposed to letting the RPC Bind service dynamically assign a port. Edit the file <...Rule Unknown Severity -
Configure statd to use static port
Configure the <code>statd</code> daemon to use a static port as opposed to letting the RPC Bind service dynamically assign a port. Edit the file <c...Rule Unknown Severity -
Configure NFS Clients
The steps in this section are appropriate for systems which operate as NFS clients.Group -
Disable NFS Server Daemons
There is no need to run the NFS server daemons <code>nfs</code> and <code>rpcsvcgssd</code> except on a small number of properly secured systems de...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 -
Disable Secure RPC Server Service (rpcsvcgssd)
The rpcsvcgssd service manages RPCSEC GSS contexts required to secure protocols that use RPC (most often Kerberos and NFS). The rpcsvcgssd service ...Rule Unknown Severity -
Specify UID and GID for Anonymous NFS Connections
To specify the UID and GID for remote root users, edit the <code>/etc/exports</code> file and add the following for each export: <pre> anonuid=<cod...Rule Unknown Severity -
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 -
Use Access Lists to Enforce Authorization Restrictions
When configuring NFS exports, ensure that each export line in <code>/etc/exports</code> contains a list of hosts which are allowed to access that e...Group -
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 -
Mount Remote Filesystems with nosuid
Add thenosuidoption to the fourth column of/etc/fstabfor the line which controls mounting of any NFS mounts.Rule Medium Severity -
Configure NFS Servers
The steps in this section are appropriate for systems which operate as NFS servers.Group
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