Resolving the Splunk ‘allowedDomainList’ Warning for Email Alerts: A Step-by-Step Guide
If you’ve configured a crucial alert action in Splunk to send an email, seeing a warning message instead of a successful notification can be frustrating. A common issue that administrators encounter is a security warning related to the allowedDomainList in the email alert action configuration.
This isn’t a bug; it’s a critical security feature designed to protect your organization’s data. Understanding why it exists and how to properly configure it is essential for maintaining a secure and functional Splunk environment.
Understanding the ‘allowedDomainList’ Security Feature
The primary purpose of the allowedDomainList parameter is to prevent potential data exfiltration. Imagine a scenario where a user with permission to create alerts—but not necessarily full administrative access—sets up an alert. If there were no restrictions, this user could configure the alert to email sensitive log data or query results to any external email address, including their personal account or an attacker’s inbox.
By enforcing an allow list of approved email domains, Splunk ensures that automated email alerts can only be sent to trusted, pre-approved destinations. This is a fundamental security control that every Splunk administrator should manage carefully.
How to Safely Configure Your Email Alert Domain List
When you try to send an email alert to a domain that isn’t on this list, Splunk will block the action and log a warning. To resolve this, you must explicitly add the desired domain(s) to your configuration. Here’s how to do it correctly.
1. Locate Your alert_actions.conf File
The settings for alert actions are controlled by the alert_actions.conf file. While a default version exists, you should never edit the default file directly. Best practice is to create or modify a local version of this file within the context of the app where the alert is configured.
The most common location to make this change is:
$SPLUNK_HOME/etc/apps/<your_app_name>/local/
If you want this setting to apply globally, you can place it in an app that is exported to all others, such as the search app:
$SPLUNK_HOME/etc/apps/search/local/
2. Edit the [email] Stanza
Open or create the alert_actions.conf file in the appropriate local directory. You will need to add or modify the [email] stanza. Within this stanza, you will find the allowedDomainList parameter.
3. Add Your Approved Domains
Modify the allowedDomainList setting to include the domains you need to send emails to. If you need to add multiple domains, separate them with a comma.
For example, if the setting is currently empty or not present, your [email] stanza might look like this:
[email]
To allow emails to be sent to addresses at mycompany.com and trustedpartner.net, you would update the stanza as follows:
[email]
allowedDomainList = mycompany.com, trustedpartner.net
It is critical to only add domains that are officially sanctioned and trusted by your organization.
4. Save the File and Restart Splunk
After you have saved your changes to alert_actions.conf, the new configuration will not take effect immediately. You must restart your Splunk instance (or the specific search head in a distributed environment) for the changes to be loaded.
After the restart, your email alerts configured to send to the newly allowed domains should function correctly without generating a warning.
Security Best Practices for Managing Your Allow List
- Adhere to the Principle of Least Privilege: Only add domains that are absolutely necessary for business operations. Avoid adding broad, public domains like
gmail.comoroutlook.comunless there is a strictly documented and approved business case. - Avoid Wildcards: While it might be tempting to use a wildcard (
*) to allow all domains, this completely negates the security feature. Never use a wildcard in theallowedDomainListin a production environment. - Regularly Audit the List: Periodically review the domains on your allow list. If a partner organization is no longer active or a business need has changed, remove the corresponding domain to tighten your security posture.
- Document Your Changes: Keep a record of why each domain was added to the list. This documentation is invaluable for security audits and for future administrators who may need to manage the configuration.
Source: https://infotechys.com/splunk-alloweddomainlist-configuration/
