In Splunk Enterprise versions below 10.4.2, 10.2.6, 10.0.9, and 9.4.14, a user that holds a role with the schedule_search capability could store a malicious script in an alert trigger condition field. When another user opens the crafted link, the script runs in the browser of that user and could access all data available to that user. The vulnerability is possible because Splunk Web uses the alert threshold value in generated alert trigger condition markup without escaping special characters. Successful exploitation requires another user to open the crafted link. For more information see Configure alert trigger conditions (https://help.splunk.com/en/splunk-enterprise/alert-and-respond/alerting-manual/10.4/manage-alert-trigger-conditions-and-throttling/configure-alert-trigger-conditions) and Define roles on the Splunk platform with capabilities (https://help.splunk.com/en/splunk-enterprise/administer/manage-users-and-security/10.2/manage-splunk-platform-users-and-roles/define-roles-on-the-splunk-platform-with-capabilities) in the Splunk documentation.
The vulnerability affects instances with Splunk Web turned on. Turning Splunk Web off is a possible workaround. See Disable unnecessary Splunk Enterprise components and the web.conf configuration specification file for more information on turning off Splunk Web.
Upgrade Splunk Enterprise to versions 10.4.2, 10.2.6, 10.0.9, and 9.4.14, or higher.