The additional_tables configuration of the page and tt_content indexers accepts arbitrary table and field names. A backend user with permission to edit indexer configurations can copy sensitive data from internal TYPO3 tables into the search index.
Exploitability
AV:NAC:LAT:PPR:HUI:NVulnerable System
VC:HVI:NVA:NSubsequent System
SC:LSI:NSA:N5.9/CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:N/VA:N/SC:L/SI:N/SA:NOther