In TYPO3 CMS greater than or equal to 9.0.0 and less than 9.5.20, and greater than or equal to 10.0.0 and less than 10.4.6, in a case where an attacker manages to generate a valid cryptographic message authentication code (HMAC-SHA1) - either by using a different existing vulnerability or in case the internal encryptionKey was exposed - it is possible to retrieve arbitrary files of a TYPO3 installation. This includes the possibility to fetch typo3conf/LocalConfiguration.php, which again contains the encryptionKey as well as credentials of the database management system being used. In case a database server is directly accessible either via internet or in a shared hosting network, this allows the ability to completely retrieve, manipulate or delete database contents. This includes creating an administration user account - which can be used to trigger remote code execution by injecting custom extensions. This has been patched in versions 9.5.20 and 10.4.6.

TYPO3 is an open source PHP based web content management system released under the GNU GPL. The plaintext value of `$GLOBALS['SYS']['encryptionKey']` was displayed in the editing forms of the TYPO3 Install Tool user interface. This allowed attackers to utilize the value to generate cryptographic hashes used for verifying the authenticity of HTTP request parameters. Exploiting this vulnerability requires an administrator-level backend user account with system maintainer permissions. Users are advised to update to TYPO3 versions 8.7.57 ELTS, 9.5.46 ELTS, 10.4.43 ELTS, 11.5.35 LTS, 12.4.11 LTS, 13.0.1 that fix the problem described. There are no known workarounds for this vulnerability.