In Splunk Enterprise versions below 10.4.3, 10.2.7, 10.0.10, and 9.4.15, a user that holds a role with the run_collect capability could use

In Splunk Enterprise versions below 10.4.3, 10.2.7, 10.0.10, and 9.4.15, a user that holds a role with the run_collect capability could use the collect Search Processing Language (SPL) command to write events to internal indexes outside the index access configured for the role. The vulnerability is possible because Splunk Enterprise does not normalize whitespace in an index name before applying configured index-access restrictions for the role. For more information see collect (https://help.splunk.com/en/splunk-enterprise/search/spl-search-reference/10.4/search-commands/collect), Define roles on the Splunk platform with capabilities (https://help.splunk.com/en/splunk-enterprise/administer/manage-users-and-security/10.4/manage-splunk-platform-users-and-roles/define-roles-on-the-splunk-platform-with-capabilities), and How indexing works (https://help.splunk.com/en/splunk-enterprise/administer/manage-indexers-and-indexer-clusters/10.4/indexing-overview/how-indexing-works) in the Splunk documentation.