Configure TLS certificates for inter-Splunk communication

You can use transport layer security (TLS) certificates to secure connections between various Splunk components. This is known as inter-Splunk communication. Typically, Splunk processes communicate on the TCP/IP network port 8089. This port is also known as the Splunk management port.

The certificates you use can replace the default certificates that Splunk provides. You can either obtain certificates from a certificate authority, or create and sign them yourself.

Prerequisites for configuring TLS certificates for inter-Splunk communication

Before you can secure communications between Splunk indexers and forwarders, you must have the following:

1. One or more TLS certificates.
   • You can either obtain third party certificates from a certificate authority, or create and sign them yourself
   • After you get the certificates, you must prepare the certificates for use with Splunk platform instances
   • The certificates must be in Privacy-Enhanced Mail format and comply with the x.509 public key certificate standard
   • You must have a private key file for each certificate file.
   • The key files that come with the certificates must comply with the Rivest-Shamir-Adelman (RSA) security algorithm.
2. Administrative access to the Splunk Enterprise instances that you want to secure
3. An understanding of Splunk configuration files

Configure TLS certificates for communications on the Splunk management port

You can configure TLS certificates on Splunk services that use the management network port.

When you configure Splunk Enterprise to use TLS certificates, upon restart, it changes the file permissions on the certificates so that only the user that Splunk Enterprise runs as has full access. This is by design, in line with security industry standards, and cannot be changed.

1. Open a shell or command prompt.
2. Using this prompt or file system management tools, copy the server certificate and the certificate authority public certificate into an accessible directory on the instance where you want to configure certificates. For example, you can move the files to a destination directory of $SPLUNK_HOME/etc/auth/mycerts/.
3. Use a text editor to open the $SPLUNK_HOME/etc/system/local/server.conf configuration file for editing.
4. In the server.conf file, configure the instance to use the server certificate. Add the following stanzas and settings to the file.

   Setting/stanza name	Data type	Description
   [sslConfig]	n/a	Sets up TLS/SSL configurations for inter-Splunk communication.
   serverCert	string	The location of the server certificate on the Splunk platform instance. This is the certificate that the machine uses to support inbound connections over TLS/SSL. You can specify either the absolute path to the certificate, such as /opt/splunk/etc/auth/mycerts/myServerCert.pem, or you can use a relative path, such as etc/auth/mycerts/myServerCert.pem and the instance uses the Splunk platform instance installation directory.
   sslPassword (Optional)	string	The password that you entered when you created the certificate, if you created a password.
   requireClientCert (Optional)	Boolean	Whether or not the Splunk platform instance requires that a connecting client present a valid TLS certificate before the connection can succeed. A value of "true" means that the receiving instance must see a valid certificate to let the client authenticate. A value of "false" means that clients can connect without presenting a certificate. Configure this setting to "true" if you want your receivers to require authentication with certificates. When both the forwarder and receiver have a "true" value for this setting, mutually authenticated TLS or mTLS is active.
   sslVersions (Optional)	comma-separated list	The list of SSL versions that the receiver supports. The Splunk platform supports the following versions for SSL and TLS: "ssl3", "tls1.0", "tls1.1", and "tls1.2".
   cipherSuite (Optional)	string	The list of cipher suite strings that the TLS/SSL sessions are to use.
   sslCommonNameToCheck (Optional except in certain circumstances)	comma-separated list	A list of one or more common names upon which the receiving Splunk platform instance checks for a match in the certificate that the client presents upon connecting to the receiver. This setting is only valid if you have configured the 'requireClientCert' setting with a value of "true". If none of the common names in this setting value matches the common name in the certificate of the connecting client, the receiving instance declines the connection as not authorized.
   sslAltNameToCheck (Optional except in certain circumstances)	comma-separated list	A list of one or more alternate names upon which the receiving Splunk platform instance checks for a match in the certificate that the client presents upon connecting to the receiver. This setting is only valid if you have configured the 'requireClientCert' setting with a value of "true". If none of the alternate names in this setting value matches the alternate name in the certificate of the connecting client, the receiving instance declines the connection as not authorized.
   sslRootCAPath	string	The location of the certificate authority certificate.

5. Save the server.conf file and close it.
6. Using the CLI, restart the splunkd process:

   # $SPLUNK_HOME/bin/splunk restart splunkd
   

Configuration file examples for configuring TLS certificates on the Splunk management port

Following is an example of a server.conf configuration file on a search head and search peer. The configuration is as follows:

• The search head uses a certificate that is in the /opt/splunk/etc/auth/mycerts directory called mySHServerCert.pem
• The instance uses a certificate authority certificate located at /opt/splunk/etc/auth/mycerts/myCACertificate.pem
• The server certificate was created with a password "mySHCertificatePassword"
• The instance requires a certificate from clients that connect to it to ensure mutually authenticated TLS (mTLS)
• The instance checks incoming certificates to ensure that the Common Name field in the certificate contains either "splunk1.mycompany.com" or "splunk2.mycompany.com"

[sslConfig]
enableSplunkdSSL = true
sslRootCAPath = /opt/splunk/etc/auth/mycerts/myCACertificate.pem
serverCert = /opt/splunk/etc/auth/mycerts/mySHServerCert.pem
sslPassword = mySHCertificatePassword
requireClientCert = true
sslVersions *,-ssl2
sslCommonNameToCheck = splunk1.mycompany.com,splunk2.mycompany.com

If you supply a password for your server certificate in the server.conf file by providing a value for the sslPassword setting, the Splunk platform encrypts that password from clear text when you restart the Splunk platform instance.

Next steps

Confirm that the forwarder and indexer configurations work properly. See Test and troubleshoot TLS connections.