When I execute one of my stored procedures manually, I have to populate several variables.
Most of the variables don't change each time it is run; is it possible to pre-populate the "Value" box so that it only needs to be changed when necessary?
I am reluctant to hard code in the script as there was a series of interlinked procedures which I need to keep dynamic
I'm going to go out on a limb here and guess that you're talking about SQL Server, and that you're executing your procedure through SSMS, because of your description of the graphical interface. In the future, please tag your question with the specific database platform that the question pertains to, and try to be responsive to early comments. You'll get answers much, much faster. (If I'm wrong, just undo the tagging I added to your question.)
Although stored procedures can contain variables, what you're talking about here are parameters; values that are passed into the procedure from the calling code or application.
Parameters can be defined with default values in their declarations.
CREATE OR ALTER PROCEDURE dbo.SomeProc (
#SomeBigIntegerValue bigint = 42
)
AS...
When default values exist, the parameter becomes optional for the caller. The procedure can now be called with or without explicit parameters. Either of these will run.
EXECUTE dbo.SomeProc;
EXECUTE dbo.SomeProc
#SomeBigIntegerValue = 37;
In the first instance, the procedure will use the default value, 42. In the second instance, it will use the parameter value, 37.
You'll note that I named the parameter in the call. That's a best practice, generally, to avoid confusion, but it also allows you to send the parameters in any order. If you don't name them, they will be interpreted in the order they're declared, so you run all manner of risks there.
If you choose to execute the procedure through the GUI, the default values won't be pre-populated, but you can see which parameters have defaults and which don't by expanding the Parameters tab under the procedure name in SSMS. I couldn't find an example with defaults, but it'll looks something like this:
If you want the procedure to use the default value, just tick the Pass Null Value check box.
(In case you're wondering, we have a truncate proc so that our ETL service accounts can have scaled back permissions without having to do fully-logged, row-by-row deletions...)
I have a stored procedure sp_1 that calls another stored procedure sp_1_1.
I know how to suppress the results from sp_1_1 using this trick.
The real problem is that sp_1_1 itself also call another stored procedure sp_1_1_1 which ALSO returns it's results to sp_1_1!!
I may not change either sp_1_1 or sp_1_1_1, and can only change sp_1.
The results returned to sp_1 are 2 recordsets, with the first from sp_1_1 and the second from sp_1_1_1.
SUMMARY:
sp_1 (Needs to suppress two recordsets returned from below)
+---- sp_1_1 (returns its own results, then results from below)
+----------sp_1_1_1 (returns results)
Firstly, an aside, SQL Server "Denali" gives you new options for handling resultsets.
In this case, because you're nesting you obviously can't use the insert/exec trick.
One kludgy workaround, if you don't want to refactor too much, is to add a parameter to the proc with a default, something like #SuppressResults bit = false.
Then, in the routines that need to be nested, call it explicitly with #SuppressResult=True, and then alter the code in the routines to not select results if #SuppressResults=True.
The important thing is to provide a default and put the parameter at the end. That will prevent existing calls to the routine from elsewhere in the code base needing to be altered.
If yes, why are there still so many successful SQL injections? Just because some developers are too dumb to use parameterized statements?
When articles talk about parameterized queries stopping SQL attacks they don't really explain why, it's often a case of "It does, so don't ask why" -- possibly because they don't know themselves. A sure sign of a bad educator is one that can't admit they don't know something. But I digress.
When I say I found it totally understandable to be confused is simple. Imagine a dynamic SQL query
sqlQuery='SELECT * FROM custTable WHERE User=' + Username + ' AND Pass=' + password
so a simple sql injection would be just to put the Username in as ' OR 1=1--
This would effectively make the sql query:
sqlQuery='SELECT * FROM custTable WHERE User='' OR 1=1-- ' AND PASS=' + password
This says select all customers where they're username is blank ('') or 1=1, which is a boolean, equating to true. Then it uses -- to comment out the rest of the query. So this will just print out all the customer table, or do whatever you want with it, if logging in, it will log in with the first user's privileges, which can often be the administrator.
Now parameterized queries do it differently, with code like:
sqlQuery='SELECT * FROM custTable WHERE User=? AND Pass=?'
parameters.add("User", username)
parameters.add("Pass", password)
where username and password are variables pointing to the associated inputted username and password
Now at this point, you may be thinking, this doesn't change anything at all. Surely you could still just put into the username field something like Nobody OR 1=1'--, effectively making the query:
sqlQuery='SELECT * FROM custTable WHERE User=Nobody OR 1=1'-- AND Pass=?'
And this would seem like a valid argument. But, you would be wrong.
The way parameterized queries work, is that the sqlQuery is sent as a query, and the database knows exactly what this query will do, and only then will it insert the username and passwords merely as values. This means they cannot effect the query, because the database already knows what the query will do. So in this case it would look for a username of "Nobody OR 1=1'--" and a blank password, which should come up false.
This isn't a complete solution though, and input validation will still need to be done, since this won't effect other problems, such as XSS attacks, as you could still put javascript into the database. Then if this is read out onto a page, it would display it as normal javascript, depending on any output validation. So really the best thing to do is still use input validation, but using parameterized queries or stored procedures to stop any SQL attacks.
The links that I have posted in my comments to the question explain the problem very well. I've summarised my feelings on why the problem persists, below:
Those just starting out may have no awareness of SQL injection.
Some are aware of SQL injection, but think that escaping is the (only?) solution. If you do a quick Google search for php mysql query, the first page that appears is the mysql_query page, on which there is an example that shows interpolating escaped user input into a query. There's no mention (at least not that I can see) of using prepared statements instead. As others have said, there are so many tutorials out there that use parameter interpolation, that it's not really surprising how often it is still used.
A lack of understanding of how parameterized statements work. Some think that it is just a fancy means of escaping values.
Others are aware of parameterized statements, but don't use them because they have heard that they are too slow. I suspect that many people have heard how incredibly slow paramterized statements are, but have not actually done any testing of their own. As Bill Karwin pointed out in his talk, the difference in performance should rarely be used as a factor when considering the use of prepared statements. The benefits of prepare once, execute many, often appear to be forgotten, as do the improvements in security and code maintainability.
Some use parameterized statements everywhere, but with interpolation of unchecked values such as table and columns names, keywords and conditional operators. Dynamic searches, such as those that allow users to specify a number of different search fields, comparison conditions and sort order, are prime examples of this.
False sense of security when using an ORM. ORMs still allow interpolation of SQL statement parts - see 5.
Programming is a big and complex subject, database management is a big and complex subject, security is a big and complex subject. Developing a secure database application is not easy - even experienced developers can get caught out.
Many of the answers on stackoverflow don't help. When people write questions that use dynamic SQL and parameter interpolation, there is often a lack of responses that suggest using parameterized statements instead. On a few occasions, I've had people rebut my suggestion to use prepared statements - usually because of the perceived unacceptable performance overhead. I seriously doubt that those asking most of these questions are in a position where the extra few milliseconds taken to prepare a parameterized statement will have a catastrophic effect on their application.
Well good question.
The answer is more stochastic than deterministic and I will try to explain my view, using a small example.
There many references on the net that suggest us to use parameters in our queries or to use stored procedure with parameters in order to avoid SQL Injection (SQLi). I will show you that stored procedures (for instance) is not the magic stick against SQLi. The responsibility still remains on the programmer.
Consider the following SQL Server Stored Procedure that will get the user row from a table 'Users':
create procedure getUser
#name varchar(20)
,#pass varchar(20)
as
declare #sql as nvarchar(512)
set #sql = 'select usrID, usrUName, usrFullName, usrRoleID '+
'from Users '+
'where usrUName = '''+#name+''' and usrPass = '''+#pass+''''
execute(#sql)
You can get the results by passing as parameters the username and the password. Supposing the password is in free text (just for simplicity of this example) a normal call would be:
DECLARE #RC int
DECLARE #name varchar(20)
DECLARE #pass varchar(20)
EXECUTE #RC = [dbo].[getUser]
#name = 'admin'
,#pass = '!#Th1siSTheP#ssw0rd!!'
GO
But here we have a bad programming technique used by the programmer inside the stored procedure, so an attacker can execute the following:
DECLARE #RC int
DECLARE #name varchar(20)
DECLARE #pass varchar(20)
EXECUTE #RC = [TestDB].[dbo].[getUser]
#name = 'admin'
,#pass = 'any'' OR 1=1 --'
GO
The above parameters will be passed as arguments to the stored procedure and the SQL command that finally will be executed is:
select usrID, usrUName, usrFullName, usrRoleID
from Users
where usrUName = 'admin' and usrPass = 'any' OR 1=1 --'
..which will get all rows back from users
The problem here is that even we follow the principle "Create a stored procedure and pass the fields to search as parameters" the SQLi is still performed. This is because we just copy our bad programming practice inside the stored procedure. The solution to the problem is to rewrite our Stored Procedure as follows:
alter procedure getUser
#name varchar(20)
,#pass varchar(20)
as
select usrID, usrUName, usrFullName, usrRoleID
from Users
where usrUName = #name and usrPass = #pass
What I am trying to say is that the developers must learn first what an SQLi attack is and how can be performed and then to safeguard their code accordingly. Blindly following 'best practices' is not always the safer way... and maybe this is why we have so many 'best practices'- failures!
Yes, the use of prepared statements stops all SQL injections, at least in theory. In practice, parameterized statements may not be real prepared statements, e.g. PDO in PHP emulates them by default so it's open to an edge case attack.
If you're using real prepared statements, everything is safe. Well, at least as long as you don't concatenate unsafe SQL into your query as reaction to not being able to prepare table names for example.
If yes, why are there still so many successful SQL injections? Just because some developers are too dumb to use parameterized statements?
Yes, education is the main point here, and legacy code bases. Many tutorials use escaping and those can't be easily removed from the web, unfortunately.
I avoid absolutes in programming; there is always an exception. I highly recommend stored procedures and command objects. A majority of my back ground is with SQL Server, but I do play with MySql from time to time. There are many advantages to stored procedures including cached query plans; yes, this can be accomplished with parameters and inline SQL, but that opens up more possibilities for injection attacks and doesn't help with separation of concerns. For me it's also much easier to secure a database as my applications generally only have execute permission for said stored procedures. Without direct table/view access it's much more difficult to inject anything. If the applications user is compromised one only has permission to execute exactly what was pre-defined.
My two cents.
I wouldn't say "dumb".
I think the tutorials are the problem. Most SQL tutorials, books, whatever explain SQL with inlined values, not mentioning bind parameters at all. People learning from these tutorials don't have a chance to learn it right.
Because most code isn't written with security in mind, and management, given a choice between adding features (especially something visible that can be sold) and security/stability/reliability (which is a much harder sell) they will almost invariably choose the former. Security is only a concern when it becomes a problem.
Can parameterized statement stop all SQL injection?
Yes, as long as your database driver offers a placeholder for the every possible SQL literal. Most prepared statement drivers don't. Say, you'd never find a placeholder for a field name or for an array of values. Which will make a developer to fall back into tailoring a query by hand, using concatenation and manual formatting. With predicted outcome.
That's why I made my Mysql wrapper for PHP that supports most of literals that can be added to the query dynamically, including arrays and identifiers.
If yes, why are there still so many successful SQL injections? Just because some developers are too dumb to use parameterized statements?
As you can see, in reality it's just impossible to have all your queries parameterized, even if you're not dumb.
First my answer to your first question: Yes, as far as I know, by using parameterized queries, SQL injections will not be possible anymore. As to your following questions, I am not sure and can only give you my opinion on the reasons:
I think it's easier to "just" write the SQL query string by concatenate some different parts (maybe even dependent on some logical checks) together with the values to be inserted.
It's just creating the query and executing it.
Another advantage is that you can print (echo, output or whatever) the sql query string and then use this string for a manual query to the database engine.
When working with prepared statements, you always have at least one step more:
You have to build your query (including the parameters, of course)
You have to prepare the query on the server
You have to bind the parameters to the actual values you want to use for your query
You have to execute the query.
That's somewhat more work (and not so straightforward to program) especially for some "quick and dirty" jobs which often prove to be very long-lived...
Best regards,
Box
SQL injection is a subset of the larger problem of code injection, where data and code are provided over the same channel and data is mistaken for code. Parameterized queries prevent this from occurring by forming the query using context about what is data and what is code.
In some specific cases, this is not sufficient. In many DBMSes, it's possible to dynamically execute SQL with stored procedures, introducing a SQL injection flaw at the DBMS level. Calling such a stored procedure using parameterized queries will not prevent the SQL injection in the procedure from being exploited. Another example can be seen in this blog post.
More commonly, developers use the functionality incorrectly. Commonly the code looks something like this when done correctly:
db.parameterize_query("select foo from bar where baz = '?'", user_input)
Some developers will concatenate strings together and then use a parameterized query, which doesn't actually make the aforementioned data/code distinction that provides the security guarantees we're looking for:
db.parameterize_query("select foo from bar where baz = '" + user_input + "'")
Correct usage of parameterized queries provides very strong, but not impenetrable, protection against SQL injection attacks.
To protect your application from SQL injection, perform the following steps:
Step 1. Constrain input.
Step 2. Use parameters with stored procedures.
Step 3. Use parameters with dynamic SQL.
Refer to http://msdn.microsoft.com/en-us/library/ff648339.aspx
even if
prepared statements are properly used throughout the web application’s own
code, SQL injection flaws may still exist if database code components construct
queries from user input in an unsafe manner.
The following is an example of a stored procedure that is vulnerable to SQL
injection in the #name parameter:
CREATE PROCEDURE show_current_orders
(#name varchar(400) = NULL)
AS
DECLARE #sql nvarchar(4000)
SELECT #sql = ‘SELECT id_num, searchstring FROM searchorders WHERE ‘ +
‘searchstring = ‘’’ + #name + ‘’’’;
EXEC (#sql)
GO
Even if the application passes the user-supplied name value to the stored
procedure in a safe manner, the procedure itself concatenates this directly into
a dynamic query and therefore is vulnerable.
I have worked on SQL stored procedures and I have noticed that many people use two different approaches -
First, to use select queries i.e. something like
Select * from TableA where colA = 10 order by colA
Second, is to do the same by constructing a query i.e. like
Declare #sqlstring varchar(100)
Declare #sqlwhereclause varchar(100)
Declare #sqlorderby varchar(100)
Set #sqlstring = 'Select * from TableA '
Set #sqlwhereclause = 'where colA = 10 '
Set #sqlorderby = 'order by colA'
Set #sqlstring = #sqlstring + #sqlwhereclause + #sqlorderby
exec #sqlstring
Now, I know both work fine. But, the second method I mentioned is a little annoying to maintain.
I want to know which one is better? Is there any specific reason one would resort to one method over the other? Any benefits of one method over other?
Use the first one. This will allow a query plan to be cached properly, apart from being the way you are supposed to work with SQL.
The second one is open to SQL Injection attacks, apart from the other issues.
With the dynamic SQL you will not get compile time checking, so it may fail only when invoked (the sooner you know about incorrect syntax, the better).
And, you noted yourself, the maintenance burden is also higher.
The second method has the obvious drawback of not being syntax checked at compile time. It does however allow a dynamic order by clause, which the first does not. I recommend that you always use the first example unless you have a very good reason to make the query dynamic. And, as #Oded has already pointed out, be sure to guard yourself against sql injection if you do go for the second approach.
I don't have a full comprehensive answer for you, but I can tell you right now that the latter method is much more difficult to work with when importing the stored procedure as a function in an ORM. Since the SQL is constructed dynamically, you have to manually create any type-classes that are returned from the stored procedure that aren't directly correlated to entities in your model.
With that in mind, there are times where you simply can't avoid constructing a SQL statement, especially when where clauses and joins depend on the parameters passed in. In my experience, I have found that stored procs that are creating large, variably joined/whered statements for EXECs are trying to do too many things. In these situations, I would recommend you keep the Single Responsibility Principle in mind.
Executing dynamic SQL inside a stored procedure reduces the value of using stored procedures to just a saved query container. Stored procedures are mostly beneficial in that the query execution plan (a very costly operation) is compiled and stored in memory the first time the procedure is executed. This means that every subsequent execution of the procedure is bypassing the query plan calculations, and jumping right to the data retrieval portiion of the operation.
Also, allowing a stored procedure to take an executable query string as a parameter is dangerous. Anyone with execute permission on granted on the procedure could potentially cause havoc on the rest of the database.
Which approach is better to use if I need a member (sp or func) returning 2 parameters:
CREATE PROCEDURE Test
#in INT,
#outID INT OUT,
#amount DECIMAL OUT
AS
BEGIN
...
END
or
CREATE FUNCTION Test
(
#in INT
)
RETURNS #ret TABLE (outID INT, amount DECIMAL)
AS
BEGIN
...
END
What are pros and cons of each approach considering that the result will passed to another stored procedure:
EXEC Foobar #outID, #outAmount
A table valued function can only be used within a scope of a single SELECT statement. It cannot perform DML, catch exceptions etc.
On the other hand, it can return a set which can immediately be joined with another recordset in the same query.
If you use DML or don't need to use the output parameters in the set-based statements, use a stored proc; otherwise create a TVF.
A stored procedure that calls a function :-) I think either will suite you... if your app uses stored procedures for querying the database, then it may be best to be consistent... if you use an ORM, it may not recognize the function... I don't think you can go wrong with either.
In one of my apps, we preferred using the function approach, to throw in another perspective.
HTH.
With the stored procedure using output parameters you will only be able to return the two values: #outID and #amount.
With the table-valued function, you will be able to return a whole set of (outID, amount) tuples. In addition, a table-valued function can be used wherever table or view expressions are allowed in queries, such as:
SELECT dbo.Test(1) AS TestValues
I would argue The output parameter approach is most desirable. This makes it more self documenting that not more than one tuple is expected and I would assume is likely to be more efficient.
I would only use a table-valued function if I needed to obtain a table of values.
If there is only one "row" in your output then it would be preferable to use output parameters in a Stored Procedure.
One exception to this is if your SP/UDF can be written as a single SELECT statement - i.e. an Inline Function - because SQL Server can make better optimizations if you ever need to do something like join it to the output of another query. You may not be doing that now, but writing an inline UDF means you won't be caught off-guard with slow-as-molasses queries and timeout reports if somebody starts using it that way in the future.
If none of that applies to you then I would use a Stored Procedure for the reasons outlined; you don't want to create the illusion of set-based semantics when you aren't actually supporting them.
Output parameters.
Multi-statement table value functions are difficult to trace and tune. Stick with the stored procedure which is easier to troubleshoot.
Also, you are limited to what you can do in a udf. Say you need to add logging, or call an extended stored proc later... you can't use a udf for this.
I think your better bet would be the SP because with the TBF (table value function) you'd have to iterate through the table to get your value.
Bear in mind that if you iterate through the table in SQL, then you'll need to use a CURSOR (which aren't too bad, but can be a little tricky to use).