What security benefits are provided by using stored procedures to access data?

Question

I have seen some guidance which recommends that you secure a database by layering all data access through stored procedures.

I know that for SQL Server, you can secure tables, and even columns against CRUD operations.

For example:

 --// Logged in as 'sa'
 USE AdventureWorks;
 GRANT SELECT ON Person.Address(AddressID, AddressLine1) to Matt;
 GRANT UPDATE ON Person.Address(AddressLine1) to Matt;

 --// Logged in as 'Matt'
 SELECT * from Person.Address;                       --// Fail
 SELECT AddressID, AddressLine1 from Person.Address; --// Succeed
 UPDATE Person.Address SET AddressLine1 = '#____ 2700 Production Way' 
        WHERE AddressID = 497;                       --// Succeed

Given that you can secure tables and even columns against CRUD operations, how does using a stored procedure provide additional security, or management of security?

Answer 1

In SQL Server you do not have to grant any direct access to tables if you properly use stored procs (that means no dynamic SQl). This means your users can only do thoses things defined by the procs. If you have any financial data at all in your database or data of a sensitive nature, only the fewest possible number of people (generally only dbas) should have direct access to the tables. This seriously reduces the risk of fraud or disgruntled employees trashing your business critical data or employees stealing personal inmformation to commit identity theft. In accounting terms this is a necessary internal control and developer convenience or personal desires to do everything dynamically from the user interface should be trumped by the insecurity of of the data. Unfortunately in all too few companies, it is not. Most developers seem to only worry about outside threats to their data, but internal ones are often far more critical.

If you restrict the user at the table level and then the user fires off a query to do a legititmate insert, it won't happen. If you give them the rights to do inserts, then they can do any adhoc insert they want and aren't just limited to the ones coming from the user interface. With stored procs, they can only do the things specifically defined by the proc.

Answer 2

Because by limiting all access to those stored procs you have established a defined interface to the database, through which all access must occur... Since you will have DENY'd Direct select, insert, update, and delete operations against the tables and views, noone can directly write sql of their own design that does whatever they want to... If you want to limit inserts into the employee table where the employee is assigned to more than three projects to to only those employees that have a score greater than 85 on a proficiency test, then you can write that constraint intoi the SaveEmployee sproc, and have it throw an exception to any client code that attempts to do that...

Sure you COULD do the same thing using client-side code, but using sProcs makes the process easier to design and manage, cause it's all in one place, and ALL applications that attempt to access this database system HAVE to conform to whatever constraints and/or security provisions you define in the SProcs... No rogue developer writing a new separate client app that hits the database can ignore or work-around a constraint or security provision in a SProc if that SProc s the ONLY WAY to insert or update a record...