13 Introducing Database Security for Application Developers

13.2.1 Are Application Users Also Database Users?

Oracle recommends that, where possible, you build applications in which application users are database users. In this way, you can leverage the intrinsic security mechanisms of the database.

For many commercial packaged applications, application users are not database users. For these applications, multiple users authenticate themselves to the application, and the application then connects to the database as a single, highly-privileged user. We will call this the One Big Application User model.

Applications built in this fashion generally cannot use many of the intrinsic security features of the database, because the identity of the user is not known to the database.

For example, use of the following features is compromised by the One Big Application User model:

13.2.2 Is Security Enforced in the Application or in the Database?

Applications, whose users are also database users, can either build security into the application, or rely upon intrinsic database security mechanisms such as granular privileges, virtual private databases (fine-grained access control with application context), roles, stored procedures, and auditing (including fine-grained auditing). Oracle recommends that applications utilize the security enforcement mechanisms of the database as far as possible.

When security is enforced in the database itself, rather than in the application, it cannot be bypassed. The main shortcoming of application-based security is that security is bypassed if the user bypasses the application to access data. For example, a user who has SQL*Plus access to the database can execute queries without going through the Human Resources application. The user, therefore, bypasses all of the security measures in the application.

Applications that use the One Big Application User model must build security enforcement into the application rather than use database security mechanisms. Because it is the application, and not the database, that recognizes users, the application itself must enforce security measures for each user.

This approach means that each application that accesses data must reimplement security. Security becomes expensive, because organizations must implement the same security policies in multiple applications. Each new application requires an expensive reimplementation.

13.4.1 An Example of Creating a Secure Application Role

Steps to create a secure application role is as follows:

1. Create the roles as application roles and specify the authorized package that will enable the roles. In this example, hr.hr_admin is the example authorized package.

   CREATE ROLE admin_role IDENTIFIED USING hr.hr_admin;
   CREATE ROLE staff_role IDENTIFIED USING hr.hr_admin;
   
   

   Note:

   You need to set up the following data structures for the examples in this section to work:

   CREATE OR REPLACE PACKAGE hr_logon IS
   PROCEDURE hr_set_responsibility;
   END;
   /
   
   CREATE OR REPLACE PACKAGE BODY hr_logon IS
   PROCEDURE hr_set_responsibility IS
      BEGIN
         DBMS_SESSION.SET_IDENTIFIER (1234);
      END;
   END;
   /
   

2. Create an invoker's right procedure.

   /* Create a dedicated authentication function for manageability so that changes in authentication policies would not affect the source code of the application - this design is up to the application developers */
   /* the only policy in this function is that current user must have been authenticated using the proxy user 'SCOTT' */
   CREATE OR REPLACE FUNCTION hr.MySecurityCheck RETURN BOOLEAN 
   AS
   BEGIN
       /* a simple check to see if current session is authenticated                                
       by the proxy user 'SCOTT' */
       if (sys_context('userenv','proxy_user') = 'SCOTT')
       then
           return TRUE;
       else
           return FALSE;
       end IF;
   END;
   
   GRANT EXECUTE ON hr.MySecurityCheck TO PUBLIC;
   
   /*Create the procedure*/
   CREATE OR REPLACE PACKAGE hr_admin
   AUTHID CURRENT_USER
   IS
   PROCEDURE hr_app_report;
   END;
   /
   CREATE OR REPLACE PACKAGE BODY hr_admin IS
   PROCEDURE hr_app_report IS
   BEGIN
       /* set application context in 'responsibility' namespace */
       hr_logon.hr_set_responsibility; 
       /* authentication check here */
       if (hr.MySecurityCheck = TRUE)
       then
            /* check 'responsibility' being set, then enable the roles without
            supplying the password */
            if (sys_context('hr','role') = 'admin' ) 
       then
            dbms_session.set_role('admin_role');
       else
            dbms_session.set_role('staff_role');
           end if;
       end if;
   END;
   END;
   

When enabling the secure application role, the database verifies that the authorized PL/SQL package is on the calling stack. This step verifies that the authorized PL/SQL package is issuing the command to enable the role. Also, when enabling the default user roles, no checking is performed for application roles.

You can use secure application roles to ensure a database connection. Because a secure application role is a role implemented by a package, the package can validate that users can connect to the database through a middle tier or from a specific IP address. In this way, the secure application role prevents users from accessing data outside an application. They are forced to work within the framework of the application privileges that they have been granted.

13.5.1 Using the SET ROLE Statement

Use a SET ROLE statement at the beginning of each application to automatically enable its associated role and to disable all others. In this way, each application dynamically enables particular privileges for a user only when required.

The SET ROLE statement simplifies privilege management. You control what information users can access and when they can access it. The SET ROLE statement also keeps users operating in a well-defined privilege domain. If a user obtains privileges only from roles, then the user cannot combine these privileges to perform unauthorized operations.

13.5.2 Using the SET_ROLE Procedure

The PL/SQL package DBMS_SESSION.SET_ROLE is functionally equivalent to the SET ROLE statement in SQL. Roles are not supported in definer's rights procedures, so the DBMS_SESSION.SET_ROLE command cannot be called from them. However, the DBMS_SESSION.SET_ROLE command can be called from the following:

• Anonymous PL/SQL blocks

• Invoker's rights stored procedures (except those invoked from within definer's rights procedures)

SET ROLE takes effect only at execution time. Because anonymous blocks compile and execute simultaneously, roles are set before security checks are performed, so the block completes successfully. With respect to invoker's rights stored procedures, if they contain static SQL statements and access to objects in the SQL are authorized through roles, then the procedure may fail during compilation (Because the roles are not enabled until the procedure executes). To resolve this problem, replace static SQL with dynamic SQL by using the DBMS_SQL package. Then, security checks are performed at execution, while at the same time the SET ROLE statement enables roles.

13.5.3 Examples of Assigning Roles with Static and Dynamic SQL

This section shows how static and dynamic SQL affect the assignment of roles.

CONNECT system/manager
DROP USER joe CASCADE;
CREATE USER joe IDENTIFIED BY joe;
GRANT CREATE SESSION, RESOURCE, UNLIMITED TABLESPACE TO joe;
GRANT CREATE SESSION, RESOURCE, UNLIMITED TABLESPACE TO scott;
DROP ROLE acct;
CREATE ROLE acct;
GRANT acct TO scott;
ALTER USER scott DEFAULT ROLE ALL EXCEPT acct;

CONNECT joe/joe;
CREATE TABLE finance (empno NUMBER);
GRANT SELECT ON finance TO acct;
CONNECT scott/tiger

Suppose you have a role named ACCT that has been granted privileges allowing you to select from table FINANCE in the JOE schema. In this case, the following procedure that uses static SQL fails:

CREATE OR REPLACE PROCEDURE statSQL_proc
AUTHID CURRENT_USER AS
    n NUMBER;
BEGIN
    SYS.DBMS_SESSION.SET_ROLE('acct');
    SELECT empno INTO n FROM JOE.FINANCE;
END;

The procedure fails because the security check that verifies that you have the SELECT privilege on table JOE.FINANCE occurs at compile time. At compile time, however, the ACCT role is not yet enabled. The role is not enabled until the procedure is executed.

In contrast, the DBMS_SQL package, which uses dynamic SQL, is not subject to this restriction. When you use this package, the security checks are performed when the procedure executes, and not when it is compiled. Thus, the following block is successful:

CREATE OR REPLACE PROCEDURE dynSQL_proc
AUTHID CURRENT_USER AS
   n NUMBER;
BEGIN
   SYS.DBMS_SESSION.SET_ROLE('acct');
   EXECUTE IMMEDIATE 'select empno from joe.finance' INTO n;
    --other calls to SYS.DBMS_SQL
END;
/

13.6.1 Unique Schemas

Most schemas can be thought of as user names: the accounts that enable users to connect to a database and access the database objects. However, unique schemas do not allow connections to the database, but are used to contain a related set of objects. Schemas of this sort are created as normal users, and yet are not granted the CREATE SESSION system privilege (either explicitly or through a role). However, you must temporarily grant the CREATE SESSION and RESOURCE privilege to such schemas if you want to use the CREATE SCHEMA statement to create multiple tables and views in a single transaction.

For example, the schema objects for a specific application might be owned by a given schema. If application users have the privileges to do so, then they can connect to the database using typical database user names and use the application and the corresponding objects. However, no user can connect to the database using the schema set up for the application. This configuration prevents access to the associated objects through the schema, and provides another layer of protection for schema objects. In this case, the application could issue an ALTER SESSION SET CURRENT_SCHEMA statement to connect the user to the correct application schema.

13.6.2 Shared Schemas

For many applications, users do not need their own accounts or schemas in a database. These users only need to access an application schema. For example, users John, Firuzeh, and Jane are all users of the Payroll application, and they need access to the Payroll schema on the Finance database. None of them need to create their own objects in the database. They need only access Payroll objects. To address this issue, Oracle Advanced Security provides enterprise users (schema-independent users).

Enterprise users, users managed in a directory service, do not need to be created as database users because they use a shared database schema. To reduce administration costs, an administrator can create an enterprise user once in the directory and point the user at a shared schema that many other enterprise users can also access.

13.7.1 What Application Developers Need to Know About Object Privileges

End users are typically granted object privileges. An object privilege allows a user to perform a particular action on a specific table, view, sequence, procedure, function, or package. Table 13-1 summarizes the object privileges available for each type of object.

13.7.2 SQL Statements Permitted by Object Privileges

As you implement and test your application, you should create each necessary role. Test the usage scenario for each role to be certain that the users of your application will have proper access to the database. After completing your tests, coordinate with the administrator of the application to ensure that each user is assigned the proper roles.

Table 13-2 lists the SQL statements permitted by the object privileges shown in Table 13-1.