CVE-2026-31888: Shopware has user enumeration via distinct error codes on Store API login endpoint

The Store API login endpoint (POST /store-api/account/login) returns different error codes depending on whether the submitted email address belongs to a registered customer (CHECKOUT__CUSTOMER_AUTH_BAD_CREDENTIALS) or is unknown (CHECKOUT__CUSTOMER_NOT_FOUND). The “not found” response also echoes the probed email address. This allows an unauthenticated attacker to enumerate valid customer accounts. The storefront login controller correctly unifies both error paths, but the Store API does not — indicating an inconsistent defense.