In SQL Server deployments, the stored procedure `User ReadBySsoUserOrganizationIdExternalId()` declares the `@ExternalId` parameter as NVARCHAR(50), whereas the queried column uses NVARCHAR(300). This discrepancy causes the SSO login identifier to be silently truncated. Consequently, a user whose identity-provider identifier starts with the full 50-character identifier of another organization member can authenticate as that member and obtain a victim-scoped access token.