Ensure that the web server user (usually www-data) has write permissions to necessary directories: sudo chown -R www-data:www-data /var/www/html/typo3/typo3conf /var/www/html/typo3/typo3temp /var/www/html/typo3/fileadmin Follow TYPO3’s security guidelines, such as keeping TYPO3 and all extensions up to date, securing file permissions, and configuring HTTPS for your site.