Is this LINQ statment vulnerable to SQL injection? - asp.net

Is this LINQ statment vulnerable to SQL injection?
var result = from b in context.tests
where b.id == inputTextBox.Text
select b;
where context is an Entity and tests is a table.
I'm trying to learn LINQ and I thought that the benefit of it was that it wasn't vulnerable to sql injection, but some stuff I've see has said differently. Would I need to parametrize this LINQ statement to make it safer? If so, How?
Also would this be considered linq to sql or linq to entities?

Short answer: LINQ is not vulnerable to SQL injection.
Long answer:
LINQ is not like SQL. There's a whole library behind the scenes that builds SQL from expression trees generated by compiler from your code, mapping the results to objects—and of course it takes care of making things safe on the way.
See LINQ to SQL FAQ:
Q. How is LINQ to SQL protected from
SQL-injection attacks?
A. SQL injection has been a significant risk for traditional SQL
queries formed by concatenating user
input. LINQ to SQL avoids such
injection by using SqlParameter in
queries. User input is turned into
parameter values. This approach
prevents malicious commands from being
used from customer input.
Internally, it means that when LINQ to SQL queries the database, instead of using plain values, it passes them as SQL parameters, which means they can never be treated as executable code by the database. This is also true for most (if not all) ORM mappers out there.
Compare these two approaches (totally pseudo-code):
string name = "' ; DROP DATABASE master --"
run ("SELECT * FROM Authors WHERE Name = '" + name + "'") // oops!
// now we'd better use parameters
SqlParameter name = new SqlParameter ("#name", "' ; DROP DATABASE master --")
run ("SELECT * FROM Authors WHERE Name = #name", name) // this is pretty safe
I suggest you dive deeper into what LINQ statements actually mean and when and how they get translated to the real SQL. You may want to learn about LINQ standard query operator translation, deferred execution, different LINQ providers et cetera. In case of LINQ, much like any abstraction technology, it is both fascinating and incredibly useful to know what's happening behind the scenes.
P.S. Everytime I see a question about SQL injection I can't help but remember this webcomic.

LINQ uses parameterized queries so it is not generally susceptible to SQL injection. Your example, for instance, isn't vulnerable.

The LINQ to Entities provider uses parametrized queries and is completely safe against SQL injection.

No. LINQ to Entities and LINQ to SQL handle the generation of SQL Queries to avoid SQL Injection. You can use LINQPad if you're curious to see what SQL statement gets generated when you run this query with various inputs.
Whether it's LINQ to SQL or LINQ to Entities depends on what your context object is, and cannot be determined from this code snippet.
The only time you need to worry about SQL injection in LINQ is if you're using the ExecuteQuery method to run a custom SQL query (see here). But at that point, you've moved away from the Language-INtegrated Query, and back into the world of generating your own strings.

LINQ To SQL generates a parameterised query so it protects against SQL injection attacks

Linq paramaterizes all queries, so isn't susceptible to SQL injection attacks. However you should still validate all of your user input as otherwise you will leave yourself open to cross site scripting attacks.

Related

Ad Hoc Query Engine -- What is it apart from the Dynamic Query part?

I understood what "AD HOC" Query means which is dynamically generating the query at run time like this if am correct
IF (someCondition)
strSQL = "SELECT * FROM authors WHERE " & whereClause
ELSE
strSQL = "SELECT * FROM authors WHERE " & whereClause & orderbyClause
Is there something Extra major concept am missing like when working with DataWarehouse etc.
Or any other link useful input will help.
An ad-hoc query engine is one that supports the full SQL language for accessing the data stored in the database. It doesn't make a difference whether the SQL is provided directly or in strings (as in your example).
Generally, it refers to complex queries on a decision support system. Ad hoc queries are frowned upon on systems that interface with lots of users or that have steady streams of data modifications.
Dynamic SQL may technically be ad hoc queries, in the sense that the string needs to be recompiled before executed. However, dynamic SQL often produces simple queries where parameterized queries would be better. Your example, for instance, is a classic example of what not to do because of SQL injection attacks.

Replacing XML with DATABASE in .NET

I've written an ASP.NET application that uses SQL SERVER Database. During modification of the Database, an experienced guru in .NET+DBMS said, one of the problems of relating/mapping multiple tables could be elegantly solved with .NET XML strings. I've never heard of this technique, but not to sound ignorant of such "hacks", I cannot ask him about it. Is there a way to INSERT/UPDATE/DELETE XML strings like a regular database table(without using Linq to XML)?
If it's not Linq to XML, then he may mean XML Columns. SQL Server 2005 onwards lets you define XML Columns in your tables. So you can have actual XML in fields in the table and you can then perform XQuery operations on them.
I do not know what your context is and what the problem statement is so I cannot tell you if this is a good or bad idea. It has its uses and can be useful in certain cases, but not in an extensive, scalable way. It really depends on what you will be using it for.
I am not sure what he meant, but it's possible to serialize your object to XML and pass the XML as a parameter to a Stored Procedure.
DECLARE #PersonJobsXML XML
SELECT #PersonJobsXML = '<PersonJobs>
<PersonId>24234</PersonId>
<Job>
<JobTitle>Engineer I</JobTitle>
<CompanyName>ACME</CompanyName>
</Job>
<Job>
<JobTitle>Engineer II</JobTitle>
<CompanyName>World Inc.</CompanyName>
</Job>
<Job>
<JobTitle>Engineer II</JobTitle>
<CompanyName>Tek Corp</CompanyName>
</Job>
</PersonJobs>'
SELECT PersonJobs.Job.value('../PersonId[1]', 'INT') AS PersonId
, PersonJobs.Job.value('JobTitle[1]', 'VARCHAR(200)') AS JobTitle
, PersonJobs.Job.value('CompanyName[1]', 'VARCHAR(200)') AS CompanyName
FROM #PersonJobsXML.nodes('//PersonJobs/Job') AS PersonJobs ( Job )
This allows you to pass a list of object to the database with just one call; the downside is that the size could be quite limited
But If you are using SQL server 2008 you should look at Table-Valued Parameters: see Table Value Parameters in SQL Server 2008 and .NET (C#)

Can I execute a scalar query in EF 4.1?

Is it possible to execute a scalar-valued query using EF 4.1?
I've tried:
ObjectQuery<int> query = new ObjectQuery<int>("select count(*) from myTable", _context);
var result = query.Execute(MergeOption.NoTracking);
return result.FirstOrDefault();
but it returns an error: The query syntax is not valid. Near term '*'
Is the only way to execute a scalar-valued query to call a stored proc?
It seems to me that you are thinking of entity framework as an "ADO.net 2.0" rather than the ORM that it is.
Rather than using it to execute SQL queries, I'd recommend using the standard entity framework Data container and using a LINQ query, as is intended with entity framework. Then it would simply be something like
myDataContainerInstance.myTable.Count()
ObjectQuery isn't analogous to the ADO.net command and doesn't execute SQL statements. Instead it is used to define queries against the object model directly. The (*) isn't valid because it isn't SQL.

The question about the basics of LINQ to SQL

I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance.
I used to think that when doing LINQ queries like
from Customer in DB.Customers where Customer.Age > 30 select Customer
LINQ gets all customers from the database ("SELECT * FROM Customers"), moves them to the Customers array and then makes a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application.
Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string
SELECT * FROM Customers WHERE Age > 30
And only when necessary it will run the query.
So my question is: am I right? And when is the query actually run?
The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem.
I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query:
from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book
The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books:
var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 && Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID;
BUT when I try to do the query now:
from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book
It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?
You are correct. LINQ to SQL does create the actual SQL to retrieve your results.
As for your shortcuts, there are ways to work around the limitations:
var popularBooksIds = DB.Sales
.Where(s => s.SalesAmount >= 50
&& s.DateOfSale >= DateTime.Now.AddDays(-10))
.Select(s => s.Id)
.ToList();
// Actually should work.
// Forces the table into memory and then uses LINQ to Objects for the query
var popularBooksSelect = DB.Books
.ToList()
.Where(b => popularBooksIds.Contains(b.Id));
Yes, query gets translated to a SQL string, and the underlying SQL can be different depending on what you are trying to do... so you have to be careful in that regard. Checkout a tool called linqpad, you can try your query in it and see the executing SQL.
Also, it runs when iterating through the collection or calling a method on it like ToList().
Entity framework or linq queries can be tricky sometimes. Sometimes you are surprised at the efficiency of the sql query generated and sometimes the query is so complicated and inefficient that you would smack your forehead.
Best idea is that if you have any suspicions about a query, run an sql profiler at the backend that would monitor all the queries coming in. That way you know exactly what is being passed on to the sql server and correct any inefficiencies if need be.
http://damieng.com/blog/2008/07/30/linq-to-sql-log-to-debug-window-file-memory-or-multiple-writers
This will help you to see what and when queries are being run. Also, Damiens blog is full of other linq to sql goodness.
You can generate an EXISTS clause by using the .Any method. I have had more success that way than trying to generate IN clauses, because it likes to retrieve all the data and pass it all back in as parameters to a query
In linq to sql, IQueryable expression fragments can be combined to create a single query, it will try to keep everything as an IQueryable for as long as it can, before you do something that cannot be expressed in SQL. When you call ToList you are directly asking it to resolve that query into an IEnumerable stored in memory.
In most cases you are better off not selecting the book ids in advance. Keep the fragment for popular books in a single place in the code and use it when necessary, to build on another query. An IQueryable is just an expression tree, which is resolved into SQL at some other point.
If you think your application will perform better by storing the popular books elsewhere (memcache or whatever), then you may consider pulling them out before hand, and checking against that later. This will mean each book id will be passed in as a sproc parameter and used in an IN clause.

Are Parameters really enough to prevent Sql injections?

I've been preaching both to my colleagues and here on SO about the goodness of using parameters in SQL queries, especially in .NET applications. I've even gone so far as to promise them as giving immunity against SQL injection attacks.
But I'm starting to wonder if this really is true. Are there any known SQL injection attacks that will be successfull against a parameterized query? Can you for example send a string that causes a buffer overflow on the server?
There are of course other considerations to make to ensure that a web application is safe (like sanitizing user input and all that stuff) but now I am thinking of SQL injections. I'm especially interested in attacks against MsSQL 2005 and 2008 since they are my primary databases, but all databases are interesting.
Edit: To clarify what I mean by parameters and parameterized queries. By using parameters I mean using "variables" instead of building the sql query in a string.
So instead of doing this:
SELECT * FROM Table WHERE Name = 'a name'
We do this:
SELECT * FROM Table WHERE Name = #Name
and then set the value of the #Name parameter on the query / command object.
Placeholders are enough to prevent injections. You might still be open to buffer overflows, but that is a completely different flavor of attack from an SQL injection (the attack vector would not be SQL syntax but binary). Since the parameters passed will all be escaped properly, there isn't any way for an attacker to pass data that will be treated like "live" SQL.
You can't use functions inside placeholders, and you can't use placeholders as column or table names, because they are escaped and quoted as string literals.
However, if you use parameters as part of a string concatenation inside your dynamic query, you are still vulnerable to injection, because your strings will not be escaped but will be literal. Using other types for parameters (such as integer) is safe.
That said, if you're using use input to set the value of something like security_level, then someone could just make themselves administrators in your system and have a free-for-all. But that's just basic input validation, and has nothing to do with SQL injection.
No, there is still risk of SQL injection any time you interpolate unvalidated data into an SQL query.
Query parameters help to avoid this risk by separating literal values from the SQL syntax.
'SELECT * FROM mytable WHERE colname = ?'
That's fine, but there are other purposes of interpolating data into a dynamic SQL query that cannot use query parameters, because it's not an SQL value but instead a table name, column name, expression, or some other syntax.
'SELECT * FROM ' + #tablename + ' WHERE colname IN (' + #comma_list + ')'
' ORDER BY ' + #colname'
It doesn't matter whether you're using stored procedures or executing dynamic SQL queries directly from application code. The risk is still there.
The remedy in these cases is to employ FIEO as needed:
Filter Input: validate that the data look like legitimate integers, table names, column names, etc. before you interpolate them.
Escape Output: in this case "output" means putting data into a SQL query. We use functions to transform variables used as string literals in an SQL expression, so that quote marks and other special characters inside the string are escaped. We should also use functions to transform variables that would be used as table names, column names, etc. As for other syntax, like writing whole SQL expressions dynamically, that's a more complex problem.
There seems to be some confusion in this thread about the definition of a "parameterised query".
SQL such as a stored proc that accepts parameters.
SQL that is called using the DBMS Parameters collection.
Given the former definition, many of the links show working attacks.
But the "normal" definition is the latter one. Given that definition, I don't know of any SQL injection attack that will work. That doesn't mean that there isn't one, but I have yet to see it.
From the comments, I'm not expressing myself clearly enough, so here's an example that will hopefully be clearer:
This approach is open to SQL injection
exec dbo.MyStoredProc 'DodgyText'
This approach isn't open to SQL injection
using (SqlCommand cmd = new SqlCommand("dbo.MyStoredProc", testConnection))
{
cmd.CommandType = CommandType.StoredProcedure;
SqlParameter newParam = new SqlParameter(paramName, SqlDbType.Varchar);
newParam.Value = "DodgyText";
.....
cmd.Parameters.Add(newParam);
.....
cmd.ExecuteNonQuery();
}
any sql parameter of string type (varchar, nvarchar, etc) that is used to construct a dynamic query is still vulnerable
otherwise the parameter type conversion (e.g. to int, decimal, date, etc.) should eliminate any attempt to inject sql via the parameter
EDIT: an example, where parameter #p1 is intended to be a table name
create procedure dbo.uspBeAfraidBeVeryAfraid ( #p1 varchar(64) )
AS
SET NOCOUNT ON
declare #sql varchar(512)
set #sql = 'select * from ' + #p1
exec(#sql)
GO
If #p1 is selected from a drop-down list it is a potential sql-injection attack vector;
If #p1 is formulated programmatically w/out the ability of the user to intervene then it is not a potential sql-injection attack vector
A buffer overflow is not SQL injection.
Parametrized queries guarantee you are safe against SQL injection. They don't guarantee there aren't possible exploits in the form of bugs in your SQL server, but nothing will guarantee that.
Your data is not safe if you use dynamic sql in any way shape or form because the permissions must be at the table level. Yes you have limited the type and amount of injection attack from that particular query, but not limited the access a user can get if he or she finds a way into the system and you are completely vunerable to internal users accessing what they shouldn't in order to commit fraud or steal personal information to sell. Dynamic SQL of any type is a dangerous practice. If you use non-dynamic stored procs, you can set permissions at the procesdure level and no user can do anything except what is defined by the procs (except system admins of course).
It is possible for a stored proc to be vulnerable to special types of SQL injection via overflow/truncation, see: Injection Enabled by Data Truncation here:
http://msdn.microsoft.com/en-us/library/ms161953.aspx
Just remember that with parameters you can easily store the string, or say username if you don't have any policies, "); drop table users; --"
This in itself won't cause any harm, but you better know where and how that date is used further on in your application (e.g. stored in a cookie, retrieved later on to do other stuff.
You can run dynamic sql as example
DECLARE #SQL NVARCHAR(4000);
DECLARE #ParameterDefinition NVARCHAR(4000);
SELECT #ParameterDefinition = '#date varchar(10)'
SET #SQL='Select CAST(#date AS DATETIME) Date'
EXEC sp_executeSQL #SQL,#ParameterDefinition,#date='04/15/2011'

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