Question

All,

In SQL Server, can a stored procedure (beeing ran from a user) write to table where the user doesn’t have access to write directly to the table?

Rgds,

MK

Answer 1

The correct answer is NO, a stored procedure does not have access to write into a table. However most users perceive it, incorrectly, as YES because of Ownership Chains:

When multiple database objects access
each other sequentially, the sequence
is known as a chain. Although such
chains do not independently exist,
when SQL Server traverses the links in
a chain, SQL Server evaluates
permissions on the constituent objects
differently than it would if it were
accessing the objects separately.
These differences have important
implications for managing security.
Ownership chaining enables managing
access to multiple objects, such as
multiple tables, by setting
permissions on one object, such as a
view.

So a procedure will be able to write into a table that the user has no permissions to write into if they form an ownership chain. This means that if the owner of the schema that contains the table is the same as the owner of the schema that contains the procedure, an ownership chain is formed and the procedure is allowed to write into the table. Since the vast majority of objects deployed in practice belong to the dbo schema, an ownership chain is almost always formed.

It is important to comprehend these details, so you can troubleshoot problems and understand why is the procedure allowed to write into the table. Erland Sommarskog has an excellent comprehensive write up on this topic: Giving Permissions through Stored Procedures. This article goes into great detail explaining all the options available. Your best option, far better than ownership chaining, is code signing.

Understanding how this works also helps understanding why dynamic SQL seems to ‘break’: running dynamic SQL is an automatic break in the ownership chain, which causes all ‘magic’ to disappear. And it also helps understand why this ‘magic’ appears not to work outside the database: cross db ownership chaining Option default value is 0.