Assume that you use Dynamic Data Masking (DDM) on a column in a table in SQL Server 2017 to mask sensitive data. When a low privileged user runs a specially crafted query, then the masked data may be exposed.
This issue is fixed in the following cumulative update for SQL Server:
About cumulative updates for SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server: