CVE-2021-41114

TYPO3 is an open source PHP based web content management system released
under the GNU GPL. It has been discovered that TYPO3 CMS is susceptible to
host spoofing due to improper validation of the HTTP Host header. TYPO3
uses the HTTP Host header, for example, to generate absolute URLs during
the frontend rendering process. Since the host header itself is provided by
the client, it can be forged to any value, even in a name-based virtual
hosts environment. This vulnerability is the same as described in
TYPO3-CORE-SA-2014-001 (CVE-2014-3941). A regression, introduced during
TYPO3 v11 development, led to this situation. The already existing setting
$GLOBALS[‘TYPO3_CONF_VARS’][‘SYS’][‘trustedHostsPattern’] (used as an
effective mitigation strategy in previous TYPO3 versions) was not evaluated
anymore, and reintroduced the vulnerability.