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'
Related
I have an application in which a Cosmos DB SQL Query is constructed dynamically, with some parts coming from untrusted user input. These parts are all string parameters in the WHERE clause and always enclosed in single quotes. For example:
SELECT * FROM c WHERE
c.prop1 = '{userInput1}' AND
STARTSWITH(c['{userInput2}'], '{userInput3}')
For various reasons it's not possible to use library features like SqlParameter to sanitize the user input, which obviously would be the ideal solution.
But given this constraint, would it be sufficient to escape backslashes and single quotes in the user input, i.e. replace \ by \\ and ' by \' , in order to avoid all SQL injection attacks?
(Updated to reflect the comment by #404)
I'm writing an R Shiny/SQLite app. In the app, I have a function that returns a column from one of the tables in my SQLite database, with the function taking the table name as an input.
Before sending the query to SQLite, the function checks that the table name equals one of the table names that the user is allowed to access. However, I am not using a parameterized query, because the term I'm changing is not a variable used for comparison but the name of the table to extract information from. (There might be a way to make this work anyway with a parameterized search, I suppose.)
My question is whether this is safe from an SQL injection? Can the query be altered on its way from the server to the database, or only from an alteration in the ui input to the server?
(Bear with me, I am new to SQLite.)
Assuming your query is being concatenated as follows:
tbl <- "yourTable"
sql <- paste0("select * from ", tbl, " where some_col = 1")
Then there should be no chance of SQL injection, assuming you check the incoming table name and verify that it matches a table name in your whitelist. Note that this step is critical here to keeping things safe. Let's say that you didn't sterilize the incoming table name. Then, consider this:
tbl <- "yourTable; delete from yourTable"
This would result in the following query being submitted for execution:
select * from yourTable; delete from yourTable where some_col = 1;
Assuming your SQLite driver allows multiple SQL statements to execute, the above hack/trick might end up deleting data from a large portion of one of your tables.
So, your approach should be safe provided that you check the table name. Note that strictly speaking the table name itself is not a parameter in a parameterized query. Rather, only the literal values in the query are parameters.
SQL query parameters cannot be used in place of a table name anyway, so comparing the table name to a list of known authorized tables is your only option.
Yes, it is safe. If you're in control of the set of values that can be interpolated into the SQL query, then you can prevent unauthorized SQL injection.
Note that some other elements of SQL queries cannot be parameters:
Any identifier, e.g. a table name, column name, or schema name.
Expressions
Lists of values in an IN ( ... ) predicate. Use one parameter per value in the list.
SQL keywords.
A query parameter can be used only in place of a single scalar value. That is, where you would use a quoted string literal, quoted date literal, or numeric literal.
The problem of SQL injection is only the user input. Nothing happens to the query on its way from the server to the database (well a malware could in theory alter it, but then even a parametrized query wouldn't help).
I.e., if you create a SQL string like this (C#):
sql = "SELECT * FROM " + tableName;
Then a user might enter a tableName like
MyTable; DROP TABLE MyTable
Guess what happens.
So, if you check the table name, you are on the safe side.
I would like to know how to accomplish this task. I've looked at CASE, DECODE or IF condition and I'm not able to make it work. My goal is to pass a block of predefined column/value pair constructed from ASP.NET data to my Oracle stored procedure. I am trying to only update certain columns out of many to preserve other columns not needing updates. So here's my set up:
Stored procedure:
UpdateSelectedColumns(myValuePairString, updatedBy)
-- Passed variable from ASP.NET, myValuePairString = 'col1 = 10,col2 = 'Dog''
-- update statement final
UPDATE MyTable
SET
col1 = 10,
col2 = 'Dog'
col3 = 'john';
COMMIT;
Thank you in advance...
Ricky
For once I'm gonna advise to not use a stored proc. There is no point here in using a stored procedure.
As it is your stored procedure would blindly accept its arguments and execute the update without adding any value. Furthermore, by using this procedure, you preclude the use of binds and exposes yourself to bugs (whenever you encouner a value with a quote '), performance hit and SQL injection vulnerability.
The advantage of PL/SQL (simple transparent binding, transparent use and reuse of cursors, strict static SQL parsing and metadata dependancy) are all pointless if you take an aribtrary string as argument and put it in a dynamic cursor.
You'll be better off to use your language native cursors and use bind variables.
If you really want to use PL/SQL, replace your single argument with a couple of tables. One for the column names, one for the variable values. You could then use DBMS_SQL to parse the statement and use appropriate bind variables. You'll need some convention to be able to parse date, number and character values. You'll need to read metadata from the database to check the datatypes. This would be a lot of code for not a bit of value.
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.
I'm not sure whether my SQL code and practise here is any good, so hopefully someone could enlighten me. In order to try and separate my DAL from the Business layer, I'm not using an SQLDataSource on the page. Instead, I've created a gridview to display the results and called an SQL command to retrieve results. I have the following SQL command:
string CommandText = "SELECT User.FName + User.Surname, Product.Name, Product.Quantity, Product.Price FROM User, Products WHERE Product.UserID = User.UserID";
The results are then loaded into a datareader and bound to the gridview control. This works fine. However, is the SQL statement inefficient? I've noticed some SQL statements have square brackets around each field, but when I try and put it around my fields, no results are displayed.
I'm also trying to merge the firstname and surname into one column, with a space between them, but the above doesn't put a space between them, and I can't seem to add a space in the SQL statement.
Finally, this all occurs in the code-behind of the shopping-cart page. However, is it insecure to have the connectionstring and above SQL statement in the codebehind? My connectionstring is encrypted within the web.config file and is called via the Configuration API.
Thanks for any help.
Firstly, using square brackets is optional in most cases (IIRC, there are very few instances where they are actually necessary, such as using keywords in the statement). Square brackets go around each identifier, for example,
SELECT [Server_Name].[Database_Name].[Table_Name].[Field_Name], ...
Secondly, to add a space, you can use SELECT User.FName + ' ' + User.Surname. You also might want to alias it - SELECT User.FName + ' ' + User.Surname AS [name]
Thirdly, keep the connection string in the web.config and encrypt it using a key.
Finally, you may want to consider introducing a data access layer into the project that can return objects from your datasource (might be worth having a look at NHibernate, LINQ to SQL or Entity Framework for this). You can then bind a collection of objects to your GridView.
Long time no SQL usage, but I don't see a problem with your query, as long as the database is designed well. To concatenate two string columns use something like this:
User.FName + ' ' + User.Surname AS UserName
Simply add a space between two strings.
As for security concerns: all other people can see is a rendered web page. If you don't expose connection string nor queries in the rendered HTML/JS code (like in comments etc.), you should not worry. The connection string stored in web.config and database structure visible in queries in server code are safe as long as the server is safe.
Try this:
string CommandText = "SELECT
User.FName + ' ' + User.Surname AS Fullname,
Product.Name,
Product.Quantity,
ProductDetail.Price
FROM
User, Products
WHERE
Product.UserID = User.UserID";
Best wishes,
Fabian