I am learning mysql now and one of the subjects it touches is the security issue when dealing with user input - one concern is the injection attack. I tried to duplicate the attack the book demonstrated like add a query $query = "select * from temp_table; drop table temp_table, which I used mysqli_query($connection,$query). Nothing happen. I changed to use mysqli_multi_query() and found it executed both statements. Finally I found that mysqli_query only runs one query each time.
my question is, if I use mysqli_query, theoretically speaking, the system shouldn't be worried on additional statement injection attack? Or, there is still any other way that the users can run additional statement even the server is using mysqli_query?
It's true that the basic mysqli_query() will only run one statement. So you don't have to worry that an SQL injection attack will trick your application into running multiple statements.
But one statement can include a subquery, or a SELECT... UNION SELECT....
One statement can read data it isn't intended to read. Or cause a huge sort that is intended to overwhelm your server as a denial-of-service attack.
Or it can simply be an error, not a malicious attack at all.
SELECT * FROM Users WHERE last_name = 'O'Reilly'; -- woops!
The solutions to SQL injection are pretty simple, and easy to follow. I don't understand why so many developers look for excuses not to write safe code.
I have multiple select queries which I want to execute asynchronously.
How can I do this in oracle sql ?
I basically want to test something and so want to simulate workload so I don't really care about the result and I know I can do this in multiple threads but this is specific and so would prefer if I can do this entirely in sql. procedures are fine though.
NOTE: there are no update queries only select.
I read about nowait but am not sure how to use it in oracle.
I tried something like -
select * from foo with(nowait) where col1="something";
This is the error I got -
with(nowait)
*
ERROR at line 3:
ORA-00933: SQL command not properly ended
The Oracle info on NOWAIT says:
Specify NOWAIT if you want the database to return control to you immediately
if the specified table, partition, or table subpartition is already locked by
another user. In this case, the database returns a message indicating that the
table, partition, or subpartition is already locked by another user.
This will not do what you want.
Asynchronous queries are an application thing, not a SQL thing. For example I can open TOAD and open a dozen windows and run long queries in all of them and still open another window and run another query. I could open a dozen instances of SQLPLUS and do the same thing. Nothing in the query lets me do this, it's in the application.
I think you could use DBMS_SCHEDULER to schedule some sql or procs that execute SQL.
However this is probably not the best way to do this
There are tools for this. The best way maybe to write a procedure you can call from the web and then you can use any performance testing tool that can make a web call...its worked for me before.
You may also consider:
http://sqlmag.com/database-performance-tuning/testing-heavy-load-simulating-multiple-concurrent-operations
My goal is to make trigger behavior to depend on some client identifier.
For example I execute a query
begin;
<specify-some-client-identifier>
insert into some_table
values('value')
commit;
And I have trigger function executing before insert:
NEW.some_filed := some_func(<some-client-identifier-spicified-above>)
So, how do I <specify-some-client-identifier> and get <some-client-identifier-spicified-above>?
You basically need some kind of variables in SQL. It is possible to do it, with multiple ways:
using GUCs
using table with variables
using temp table with variables
using %_SHARED in plperl functions
All this is possible. If you're interested in implementation details and/or comparison - check this blogpost - just in case it wasn't obvious from domain - it's my blog.
You will find this prior answer informative. There I explain how to pass an application-defined username through so it is visible to PostgreSQL functions and triggers.
You can also use the application_name GUC, which can be set by most client drivers or explicitly by the application. Depending on your purposes this may be sufficient.
Finally, you can examine pg_stat_activity to get info about the current client by looking it up by pg_backend_pid(). This will give you a client IP and port if TCP/IP is being used.
Of course, there's also current_user if you log in as particular users at the database level.
As usual, #depesz points out useful options I hadn't thought of, too - using shared context within PL/Perl, in particular. You can do the same thing in PL/Python. In both cases you'll pay the startup overhead of a full procedural language interpreter and the function call costs of accessing it, so it probably only makes sense to do this if you're already using PL/Perl or PL/Python.
We have many SQL Server scripts. But there are a few critical scripts that should only be run at certain times under certain conditions. Is there a way to protect us from ourselves with some kind of popup warning?
i.e. When these critical scripts are run, is there a command to ask the user if they want to continue?
(We've already made some rollback scripts to handle these, but it's better if they not be accidentally run at all).
No, there is no such thing.
You can write an application (windows service?) that will only run the scripts as and when they should be.
The fact that you are even asking the question shows that this is something that should be automated, the sooner the better.
You can mitigate the problem in the meanwhile by using if to test for these conditions and only execute if they are met. If this is a series of scripts you should wrap them in transactions to boot.
One work-around you can use is the following, which would require you to update a value in another table:
CREATE PROC dbo.MyProc
AS
WHILE (SELECT GoBit FROM dbo.OKToRun) = 0
BEGIN
RAISERROR('Waiting for GoBit to be set!', 0,1)
WAITFOR DELAY '00:00:10'
END
UPDATE dbo.OKtoRun
SET GoBit = 0
... DO STUFF ...
This will require you to, in another spid or session, update that table manually before it'll proceed.
This gets a lot more complicated with multiple procedures, so it will only work as a very short-term workaround.
sql is a query language. does not have ability to accept user inputs.
only thing i can think of would be to have it #variable driven. first part should update #shouldRunSecond = 1. and the second part should be wrapped in a
if #shouldRunSecond = 1
begin
...
end
second portion will be skipped if not desired.
The question is - where are these scripts located ?
If you have them as .sql file that you open every time before you run, then you can simply add some "magic numbers" before beginning of the script, that you will have to calculate every time, before you run it. In example below each time before you run your script you have to put correct date and minute into IF fondition, other wise script will not run
IF DATEPART(dd,GETDATE())!=5 or DATEPART(mi,(GETDATE()))!=43
BEGIN
RAISERROR ('You have tried occasionally to run your dangerous script !!!',16,1);
RETURN
END
--Some dangerous actions
drop database MostImportantCustomer
update Personal set Bonus=0 where UserName=SUSER_SNAME()
If your scripts reside in stored procedure - you can add some kind of "I am sure, I know what I do" parameter, where you will always pass, for example Minute multiplied by Day.
Hote it helps
I have seen batch scripts containing SQLCMD ..., so instead of running the .sql script from code or management studio, you could add a prompt in the script.
I have (on limited occasion) created an #AreYouSure parameter that must be passed into a stored procedure, then put comments next to the declaration in the stored procedure explaining the danger of running said procedure.
At least that way, no RANDOs will wander into your environment and kick off stored procedures when they don't understand the consequences. The parameter could be worked into an IF statement that checks it's value, or it doesn't really have to be used at all, but if it must be passed, then they have to at least figure out what to pass.
If you use this too much, though, others may just start passing a 'Y' or a 1 into every stored procedure without reading the comments. You could switch up the datatypes, but at some point it becomes more work to maintain this scheme than it is worth. That is why I use it on limited occasion.
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.