13 Security Considerations for Using Oracle Data Redaction

It is important to understand general guidelines for using Oracle Data Redaction.

• Oracle Data Redaction is not intended to protect against attacks by regular and privileged database users who run ad hoc queries directly against the database.

• Oracle Data Redaction is not intended to protect against users who run ad hoc SQL queries that attempt to determine the actual values by inference.

• Oracle Data Redaction relies on the database and application context values. For applications, it is the responsibility of the application to properly initialize the context value.

• Oracle Data Redaction is not enforced for users who are logged in using the SYSDBA administrative privilege.

• Certain DDL statements that attempt to copy the actual data out from under the control of a data redaction policy (that is, CREATE TABLE AS SELECT, INSERT AS SELECT) are blocked by default, but you can disable this behavior by granting the user the EXEMPT REDACTION POLICY system privilege.

• Oracle Data Redaction does not affect day-to-day database operations, such as backup and recovery, Oracle Data Pump exports and imports, Oracle Data Guard operations, and replication.

• Do not include any redacted columns in a SQL expression that is used in a GROUP BY clause in a SQL statement. Oracle does not support this behavior, and raises an ORA-00979: not a GROUP BY expression error. This happens because internally the expression in the SELECT list must be modified by Data Redaction, but this causes it to no longer be found when it comes time to process the GROUP BY clause (which is currently not updated by Data Redaction) leading to this unintended error message.

You can restrict the list of users who can create, view and edit Data Redaction policies by limiting who has the EXECUTE privilege on the DBMS_REDACT package and by limiting who has the SELECT privilege on the REDACTION_POLICIES and REDACTION_COLUMNS views.

You also can restrict who is exempted from redaction by limiting the EXEMPT REDACTION POLICY privilege. If you use Oracle Database Vault to restrict privileged user access, then you can use realms to restrict granting of EXEMPT REDACTION POLICY.

Both users SYS and SYSTEM automatically have the EXEMPT REDACTION POLICY system privilege.

SYSTEM has the EXP_FULL_DATABASE role, which includes the EXEMPT REDACTION POLICY system privilege.

This means that the SYS and SYSTEM users can always bypass any existing Oracle Data Redaction policies, and will always be able to view data from tables (or views) that have Data Redaction policies defined on them.

Follow these guidelines:

• Do not create Data Redaction policies on the default Oracle Database schemas, including the SYS and SYSTEM schemas.

• Be aware that granting the EXEMPT DATA REDACTION system privilege to additional roles may enable users to bypass Oracle Data Redaction, because the grantee role may have been granted to additional roles.

• Do not revoke the EXEMPT DATA REDACTION system privilege from the roles that it was granted to by default.

Be careful when writing a policy expression that depends on a SYS_CONTEXT attribute that is populated by an application, because the application might not always populate that attribute.

If the user somehow connects directly (rather than through the application), then the SYS_CONTEXT attribute would not have been populated. If you do not handle this NULL scenario in your policy expression, you could unintentionally reveal actual data to the querying user.

For example, suppose you wanted to create a policy expression that intends to redact the query results for everyone except users who have the client identifier value of SUPERVISOR. The following expression unintentionally enables querying users who have NULL as the value for their CLIENT_IDENTIFIER to see the real data:

SYS_CONTEXT('USERENV', 'CLIENT_IDENTIFIER') IS NOT 'SUPERVISOR'

A more rigorous policy expression redacts the result of the query if the client identifier is not set, that is, it has a NULL value.

SYS_CONTEXT('USERENV', 'CLIENT_IDENTIFIER') IS NOT 'SUPERVISOR' OR IS NULL

Remember that in SQL, comparisons with NULL are undefined, and are thus FALSE, but redaction only takes place when the policy expression evaluates to TRUE.

You can create Oracle Data Redaction policies on materialized views and on their base tables.

However, ensure that the creator of the materialized view, or the user who performs the refresh of the materialized view, is not blocked by any Data Redaction policies. In other words, the user performing the materialized view creation or refresh operations should be exempt from the Data Redaction policy. As a best practice, when you create a new materalized view, treat it as a copy of the actual table, and then create a separate Data Redaction policy to protect it.

You should check if the recycle bin is enabled when you drop Oracle Data Redaction policies.

If you drop a table or view that has an Oracle Data Redaction policy defined on it when the recycle bin feature is enabled, and if you query the REDACTION_COLUMNS or REDACTION_POLICIES data dictionary views before you purge the recycle bin, then you will see object names such as BIN$... (for example, BIN$1Xu5PSW5VaPgQxGS5AoAEA==$0).

This is normal behavior. These policies are removed when you purge the recycle bin.

To find if the recycle bin is enabled, you can run the SHOW PARAMETER RECYCLEBIN command in SQL*Plus.