TYPO3 is an enterprise content management system. Starting in version 9.0.0 and prior to versions 9.5.48 ELTS, 10.4.45 ELTS, 11.5.37 LTS, 12.4.15 LTS, and 13.1.1, the "ShowImageController" ("_eID tx_cms_showpic_") lacks a cryptographic HMAC-signature on the "frame" HTTP query parameter (e.g. "/index.php?eID=tx_cms_showpic?file=3&...&frame=12345"). This allows adversaries to instruct the system to produce an arbitrary number of thumbnail images on the server side. TYPO3 versions 9.5.48 ELTS, 10.4.45 ELTS, 11.5.37 LTS, 12.4.15 LTS, 13.1.1 fix the problem described.