TYPO3 is an open source, PHP based web content management system. By design, the file management module in TYPO3’s backend user interface has historically allowed the upload of any file type, with the exception of those that are directly executable in a web server context. This lack of restriction means it is possible to upload files that may be considered potentially harmful, such as executable binaries (e.g., .exe files), or files with inconsistent file extensions and MIME types (for example, a file incorrectly named with a .png extension but actually carrying the MIME type application/zip) starting in version 9.0.0 and prior to versions 9.5.51 ELTS, 10.4.50 ELTS, 11.5.44 ELTS, 12.4.31 LTS, and 13.4.12 LTS.

Although such files are not directly executable through the web server, their presence can introduce indirect risks. For example, third-party services such as antivirus scanners or malware detection systems might flag or block access to the website for end users if suspicious files are found. This could negatively affect the availability or reputation of the site.

Users should update to TYPO3 version 9.5.51 ELTS, 10.4.50 ELTS, 11.5.44 ELTS, 12.4.31 LTS, or 13.4.12 LTS to fix the problem.