Shopware is an open commerce platform. The store-API works with regular entities and not expose all fields for the public API; fields need to be marked as ApiAware in the EntityDefinition. So only ApiAware fields of the EntityDefinition will be encoded to the final JSON. Prior to versions 6.6.5.1 and 6.5.8.13, the processing of the Criteria did not considered ManyToMany associations and so they were not considered properly and the protections didn't get used. This issue cannot be reproduced with the default entities by Shopware, but can be triggered with extensions. Update to Shopware 6.6.5.1 or 6.5.8.13 to receive a patch. For older versions of 6.2, 6.3, and 6.4, corresponding security measures are also available via a plugin.
https://github.com/shopware/shopware/security/advisories/GHSA-hhcq-ph6w-494g
https://github.com/shopware/shopware/commit/ad83d38809df457efef21c37ce0996430334bf01
https://github.com/shopware/shopware/commit/8504ba7e56e53add6a1d5b9d45015e3d899cd0ac
https://github.com/shopware/core/commit/d35ee2eda5c995faeb08b3dad127eab65c64e2a2
https://github.com/shopware/core/commit/a784aa1cec0624e36e0ee4d41aeebaed40e0442f