Shopware is an open source eCommerce platform. In versions prior to 6.4.1.1 the admin api has exposed some internal hidden fields when an association has been loaded with a to many reference. Users are recommend to update to version 6.4.1.1. You can get the update to 6.4.1.1 regularly via the Auto-Updater or directly via the download overview. For older versions of 6.1, 6.2, and 6.3, corresponding security measures are also available via a plugin.
https://github.com/shopware/platform/security/advisories/GHSA-gpmh-g94g-qrhr
https://github.com/shopware/platform/commit/b5c3ce3e93bd121324d72aa9d367cb636ff1c0eb
https://docs.shopware.com/en/shopware-6-en/security-updates/security-update-06-2021