CVE-2025-11850: Improper Implicit Association via User Store Initialization in WSO2 Identity Server [Identity Confusion / External IDP Use]

When secondary user stores are configured, the implicit-association resolver incorrectly initializes from a secondary user store and bypasses the primary user store during search and uniqueness checks. This allows a subject to be associated with an unintended local account if the same lookup claim (e.g., username or email) exists in both the primary and a secondary store.

If duplicate claim values exist across user stores, this issue can lead to identity confusion due to incorrect implicit associations when using an external Identity Provider (IDP). Legitimate user accounts in the primary user store may fail to associate correctly with their corresponding external IDP accounts, potentially restricting access if the secondary account has fewer privileges. Deployments are not affected if no secondary user stores are configured, implicit association is disabled, or claim values are globally unique.