HTTP caching is marking private HTTP headers as public
Fixed in recommend updating to the current version 6.4.8.2. You can get the update to 6.4.8.2 regularly via the Auto-Updater or directly via the download overview.
https://www.shopware.com/en/download/#shopware-6
For older versions of 6.1, 6.2, and 6.3, corresponding security measures are also available via a plugin. For the full range of functions, we recommend updating to the latest Shopware version.