I need to run sql statements from the application itself. i.e. the user can go into the asp.net applciation, gets a box and can run sql statements from there
I am already doing something like this
Can I rollback Dynamic SQL in SQL Server / TSQL
That is running dynamic sql
is there a better way to do this
Dynamic SQL is certainly the easiest way to do this. The alternative is parameterized SQL, but that would require having your users define and set parameters separately from the T-SQL.
You can simply submit the T-SQL string to SQL Server using the SqlCommand object; there's no real benefit to wrapping it in an EXEC or anything, as in the link you provided. You can do exception handling on the .NET side.
Also, if you want to support command batches, keep in mind that SqlClient and friends don't understand "GO", which also isn't an actual T-SQL command -- you will need to parse the input and break it into batches yourself.
I'm sure you understand that there is a big security risk in doing this, and that's it's generally not recommended. You might consider using a connection string that specifies a user with limited permissions, to help control / limit their access.
DO NOT DO THIS. What if the user types in sp_msforeachtable 'truncate table ?'...?
RunSQL.aspx utility might help. See Upload T-SQL and execute at your hosting provider using an ASP.NET page.
Related
Problem
I'm writing a GUI application that allows users to generate an Excel file based on SELECT SQL query user enters in TextBox. It will connect to SQL server, run select over database, fill DataTable object and push that data to an Exel file.
The way I have developed application is vulnerable for SQL injections and user may be able to pass any DML query such as DELETE OR UPDATE.
Question
Is there a way in SQLCLient library to prevent user from entering DML queries and executing them? Can I somehow enforce SQLCommand object to throw an exception when DELETE command is passed?
The correct way to do this is to create a database user with only select grants to the specified tables or views as described by BhavO and jean in comments.
Why is this the correct way to limit the T-SQL commands?
Doing it client-side is significantly more complex. There is a T-SQL parser library that is provided by Microsoft, but do you really want to spend your time writing and testing tree visitor code that ensures you only have SELECT commands that only query some certain tables? Also now you have to worry about keeping this parser library component up-to-date with SQL Server releases which might have new SELECT query syntax that is not understood by the older parser library and causes errors in your app. Why not delegate the T-SQL parsing to the component in your system that is already designed to do that, which is SQL Server?
Doing it client-side provides no actual security. Security of a server needs to be implemented by the server, not by its client code. The client code is running on the user's machine, so the user has total control over what is being executed. This means a malicious user can potentially (1) decompile and edit out the "DML disable" check component and then run the edited binaries, therefore skipping the check, or more practically (2) use network inspection tools to determine how your client app is connecting to the service (i.e. the connection string) and then just directly connect using that connection string in SSMS or SQLCMD or whatever and own your server. So all of the complicated parsing logic really hasn't slowed down an attacker at all.
These reasons are (among others) why GRANT, DENY and so on exist in SQL Server in the first place. They are good (mature, well-tested, easy-to-use) tools that are implemented in the correct place in the stack.
Create a database user with only select grants, and use this user for the connection, and then handle database SqlException when executing the command.
We are building a reporting framework into our application, which necessitates the use of a query builder. Ultimately, we want power users to be able to build SELECT queries to be used to populate the report dataset.
Datasets are built using a DataAdapter (either MSSQL or SQLite). Are there any tools we can use to ensure that the queries built by the end user can only be SELECT statements?
EDIT:
As mentioned above, we target SQLite as one of our supported backends No DB permissions can be set on this platform.
Set right permissions to DB. It's the best solution.
EDIT:
For SQLLite you can set read only permissions for file - in the file system.
Give the user that you execute the SQL as only the db_datareader permission to ensure that they cannot do anything but read the data.
This question gives more info on how to do that:
How to give a user only select permission on a database
If the query builder is done in house, and if your query builder returns a the SQL statement in a string, you can parse it either looking for Update statements keyworks or with Regex, if you want to spare the users the trouble of creating an update query then realizing that they can't run it, then you should consider doing this check continiously as they create the query. Alternatively, you can use a third party query builder, like this one: http://www.activequerybuilder.com/, unfortunately i belive it doesn't support anything else but Select statements but it may be worth the shot.
I think all you have to do is wrap the QueryBuilder and expose only permited operations.
I is not good to do thinks the other way around, like letting the user construct a query and at the end you tell him it is not permissable.
I have an .NET application which is running the following statement using SqlCommand:
DECLARE #SQL VARCHAR(100)
SELECT #SQL = 'CREATE DATABASE ' + #DB
EXEC(#SQL)
The #DB parameter comes from user input, so obviously the application is vulnerable to something like 'X DROP DATABASE Y'. I'm sure there must be an obvious way I'm missing...
Edit: using a parametrized statement cannot work because you cannot use a parameter in CREATE DATABASE (CREATE DATABASE #DB returns a syntax error).
First, you should never, ever do this from a web app. Ever. Really. I'm serious. With the exception of deployment packages, the only time I've needed to execute a CREATE DATABASE is from the query analyzer in SSMS. Additionally, I'm suspicious of any code that would let a user enter a database name, and then go and create it.
Most importantly, what you've posted is not a "parameterized query." It's concatenated SQL, which is the source of SQL injection vulnerabilities.. If it were a parameterized query (or a stored proc, but I don't think you can do a CREATE DATABASE from a sproc), SQL injection would be a non-issue.
You can either use a real parametrized query (here is a good tutorial on parametrized queries.), or sanitize your inputs, but ADO.NET or whatever other db library will reliably handle this for you IF you properly build the command and parameter objects.
You probably want to specify parameters - paramaterized queries pretty much eliminate SQL injection attacks (as long as you're not concatenating strings in your receiving stored procedures).
Like I said in my comment, I hope there's an exceptionally good reason for creating databases/tables on the fly where creating rows seems to work for most everyone else.
Use a whitelist approach: allow only letters.
I've got fields that are free-form text and allow just about any combination of numbers/symbols. What's the best way to validate these to prevent SQL Injection? Can I run a simple replace of tick marks? Is there a method out there I can plug in to use?
Just use parameterized queries! Check out this article here: http://www.functionx.com/aspnet/sqlserver/parameterized.htm
There are various methods outlined here:
How To: Protect From SQL Injection in ASP.NET
quote:
Countermeasures include using a list of acceptable characters to constrain input, using parameterized SQL for data access, and using a least privileged account that has restricted permissions in the database. Using stored procedures with parameterized SQL is the recommended approach because SQL parameters are type safe. Type-safe SQL parameters can also be used with dynamic SQL. In situations where parameterized SQL cannot be used, consider using character escaping techniques.
Validation controls can help, though run them server side, not client side. ASP.NET does have some protection built in also, but I wouldn't rely on it alone.
Getting data into and out of SQL tables with C#
I built a C# app that puts data into a SQL table.
I am currently using the SqlConnection class in .net.
Got started with this article.
http://www.codeproject.com/KB/database/sql_in_csharp.aspx
I had thought about looking at Linq to SQL but have not done it before and wasn't sure how to get up and going.
Well today I ran across a bug where I was trying to add data that include a "'" in it which broke my insert statement. I got to doing some research and am starting to wonder what other problems are lurking. What if I try to add the data "drop table"?
My question is, is there a better model for data insertion? Do I look at Linq? Or do I check all my data before it is entered?
You discovered SQL Injection Attacks. It is not good policy to just append user supplied data to a SQL query for exactly the reason you specified. Any user of your system could try to steal or corrupt your data by injecting some SQL.
The way to deal with it is described in the link, but basically you specify the parameters and let the supplied classes handle properly escaping the data so that if someone passes "Drop Table", it will simply be entered as data.
Here's a great example from CodeBetter.com
SqlCommand command = connection.CreateCommand();
command.CommandText = "SELECT * FROM Customers WHERE CustomerID = #CustomerID";
command.Parameters.Add(
new SqlParameter("#CustomerID", SqlDbType.NChar, 5)).Value = customerID;
Alternatively, feel free to use LINQ to SQL. It will handle this for you and is much easier to work with from a developer perspective. You can drag and drop your database into your code and it will completely map every table. Then you can write LINQ's version of SQL statements right in your code where you'll get code completion and Compile time checking for errors. This SO question will get you started.
Here's some simple LINQ code that lets you read a customer from the database, write his/her name to the screen, then update his personalized greeting (all safe from SQL injection):
Customer myCustomer = (
from cust in myDatabase.Customers
where cust.CustomerID == userPassedCustomerID
select cust).Single();
Console.WriteLine(myCustomer.FullName);
myCustomer.PersonalizedGreeting = userPassedGreeting;
myDatabase.SubmitChanges();
The best way to work with database queries that need to be mingled with user input is to parameterized them. Now LINQ to SQL will do this for you but plain old ADO.NET lets you do it too (as the article I linked describes).
This works whether you are calling stored procedures or creating dynamic queries in your application to send to your RDBMS.
It appears you were doing some dynamic SQL, i.e. creating SQL statements on the fly, using various string manipulations in C# and then running these.
This way of doing is very versatile but introduces the risk of SQL injection. This was an accidental situation, self inflicted, but assuming that some of the elements used in building the SQL statement are provided by way of html fields, an malicious user could craft a particular string to effectively "DROP TABLE" or worse...
There are many ways to work around this situation, the most common one being to use parametrized SQL templates. With this technique, the variable parts of a SQL statement are provided to SQL in separate arguments (called parameter at the level of SQL). The ADO Command object is the vehicle used for invoking parametrized queries.
LINQ to SQL could also be used to handle this type of thing as well.