Is it possible to add the alias of a column as an SqlParameter to an SQL command? If so, how is it specified?
As a simplified example, say I have an SQL command that is constructed like this:
SqlCommand GetCommand(string columnName)
{
string filter = String.Format("SELECT MyColumn1 AS '{0}' FROM MyTable", columnName);
return new SqlCommand(filter);
}
This command does nothing to prevent an SQL Injection attack, so I want to follow the standard procedure and parameterize the command.
I'm used to converting statements in the WHERE clause to use parameters. The statements look similar to the above, for example:
SqlCommand command("SELECT * FROM MyTable WHERE name = '{0}'", name);
When I convert this, it becomes:
SqlCommand command("SELECT * FROM MyTable WHERE name = #name");
command.Parameters.Add(new SqlParameter("name", SqlDbType.NVarChar) { Value = name });
That works well. Taking the same approach here with the GetCommand() method gives:
SqlCommand GetCommand(string columnName)
{
string filter = "SELECT MyColumn1 AS #columnName FROM MyTable";
SqlCommand command = new SqlCommand(filter);
command.Parameters.Add(new SqlParameter("columnName", SqlDbType.NVarChar)
{ Value = columnName });
return command;
}
But, when the command is executed, it results in:
An exception of type 'System.Data.SqlClient.SqlException' occurred in MyApplication.exe but was not handled in user code
Additional information: Incorrect syntax near '#columnName'.
I see there are plenty of questions on SO and the web in general about use of SqlParameter, but seemingly none that touch on their use with column aliases.
There's no indication in Microsoft's SqlParameter documention either. From this, I noticed that the SqlParameter.Direction property defaults to ParameterDirection.Input; the column alias is used in output, so I tried InputOutput and Output, but it made no difference to the results.
Short answer: you can't.
Column Aliases are not parameterizable. They are identifiers in the SQL language, not values - just like the column name itself, or the table name.
"Get me column X from table Y and name it Z in the result set." None of X, Y or Z are parameterizable.
Note that this is not a limitation of SqlParameter but of the SQL language as implemented by Sql Server.
Parameters are not designed for aliasing TSQL columns. If you need an alias, just give it one in the TSQL. Additionally, the In/Out aspect of the parameter is for cases where the query modifies the parameter during running. Such as an output parameter of a stored procedure.
In truth, what it appears you're trying to do is get a dataset where the returned column name is based upon an inputted value.
I would use a data adapter to fill a data table, and then just rename the column to the desired value.
dataTable.Columns["MyColumn1"].ColumnName = columnName;
Strange thing to do, but you can build some sql with the parameter and then exec it.
Declare #sql VarChar(255)
Set #sql = 'SELECT ClientNumber AS ' + #columnName + ' FROM Ib01'
Exec(#sql)
You can't parameterize schema names and aliases. If you must have dynamic aliases, you'll need to protect yourself from SQL injection in the application layer.
Consider creating a whitelist of valid aliases, and only select from the whitelist.
If the alias comes from user input, you'll have to validate/sanitize the input.
Edit: It's a bad practice to rely on the application layer to prevent SQL injection attacks. But sometimes business drivers or other reasons force this to happen. My suggestions here are ways to mitigate the risk of SQL injection if you are forced to do this.
Related
I'm trying to set up so that the table name is passed to the command text as a parameter, but I'm not getting it to work. I've looked around a bit, and found questions like this: Parameterized Query for MySQL with C#, but I've not had any luck.
This is the relevant code (connection == the MySqlConnection containing the connection string):
public static DataSet getData(string table)
{
DataSet returnValue = new DataSet();
try
{
MySqlCommand cmd = connection.CreateCommand();
cmd.Parameters.AddWithValue("#param1", table);
cmd.CommandText = "SELECT * FROM #param1";
connection.Open();
MySqlDataAdapter adap = new MySqlDataAdapter(cmd);
adap.Fill(returnValue);
}
catch (Exception)
{
}
finally
{
if (connection.State == ConnectionState.Open)
connection.Close();
}
return returnValue;
}
If I change:
cmd.CommandText = "SELECT * FROM #param1";
to:
cmd.CommandText = "SELECT * FROM " + table;
As a way of testing, and that works (I'm writing the xml from the dataset to console to check). So I'm pretty sure the problem is just using the parameter functionality in the wrong way. Any pointers?
Also, correct me if I'm mistaken, but using the Parameter functionality should give complete protection against SQL injection, right?
You can not parameterize your table names, column names or any other databse objects. You can only parameterize your values.
You need to pass it as a string concatenation on your sql query but before you do that, I suggest use strong validation or white list (only fixed set of possible correct values).
Also, correct me if I'm mistaken, but using the Parameter
functionality should give complete protection against SQL injection,
right?
If you mean parameterized statements with "parameter functionality", yes, that's correct.
By the way, be aware, there is a concept called dynamic SQL supports SELECT * FROM #tablename but it is not recommended.
As we have seen, we can make this procedure work with help of dynamic
SQL, but it should also be clear that we gain none of the advantages
with generating that dynamic SQL in a stored procedure. You could just
as well send the dynamic SQL from the client. So, OK: 1) if the SQL
statement is very complex, you save some network traffic and you do
encapsulation. 2) As we have seen, starting with SQL 2005 there are
methods to deal with permissions. Nevertheless, this is a bad idea.
There seems to be several reasons why people want to parameterise the
table name. One camp appears to be people who are new to SQL
programming, but have experience from other languages such as C++, VB
etc where parameterisation is a good thing. Parameterising the table
name to achieve generic code and to increase maintainability seems
like good programmer virtue.
But it is just that when it comes to database objects, the old truth
does not hold. In a proper database design, each table is unique, as
it describes a unique entity. (Or at least it should!) Of course, it
is not uncommon to end up with a dozen or more look-up tables that all
have an id, a name column and some auditing columns. But they do
describe different entities, and their semblance should be regarded as
mere chance, and future requirements may make the tables more
dissimilar.
Using table's name as parameter is incorrect. Parameters in SQL just works for values not identifiers of columns or tables.
One option can be using SqlCommandBuilder Class, This will escape your table name and not vulnerable to SQL Injection:
SqlCommandBuilder cmdBuilder = new SqlCommandBuilder();
string tbName = cmdBuilder.QuoteIdentifier(tableName);
You can use the tbName in your statement because it's not vulnerable to SQL Injection now.
My Code:
SqlCommand command = new SqlCommand("SELECT min(Score) FROM MenAthletics WHERE [(#sportevent)] < (#result);", connect);
command.Parameters.AddWithValue("#sportevent", sportEvent);
command.Parameters.AddWithValue("#result", result);
the #result works fine (just a double variable)
the #sportevent doesnt't work (error: invalid columnname) (sportEvent is a string)
how can I choose a column by giving in a string?
You can parameterize values in SQL statements, but you cannot parameterize column or table names. You need to change the column name in the SQL string itself, for example, with string.Format:
SqlCommand command = new SqlCommand(
string.Format("SELECT min(Score) FROM MenAthletics WHERE [{0}] < (#result);", sportEvent)
, connect
);
command.Parameters.AddWithValue("#result", result);
Make sure that the column name does not come from user's input, otherwise you would open up your code to SQL injection attacks. In case the column name does come from user's input, you can validate the string against a list of available table columns, which could be made statically or by examining the structure of your table at runtime.
You could dynamically build the SQL query, instead of passing the column name as a parameter.
You can't use a column name as a parameter; you should instead consider constructing your query this way:
SqlCommand command =
new SqlCommand(
String.Format(#"SELECT min(Score)
FROM MenAthletics WHERE [{0}] < #result;",
sportEvent),
connect);
command.Parameters.AddWithValue("#result", result);
This kind of sql is called "dynamic sql" and can be an effective way of constructing queries on the fly.
However, there are pitfalls. As well as validating the user input, also make sure that the user you are connecting to the database with only has enough permissions to carry out the actions you want to do.
Another approach, which is less elegant, but can be placed directly into a stored procedure, is to use a CASE statement;
For example:
SELECT min(Score)
FROM MenAthletics
WHERE
CASE
WHEN #sportEvent = 'SomeColumnName' THEN SomeColumnName
WHEN #sportEvent = 'SomeColumnName2' THEN SomeColumnName2
END < #result;
This gets very tedious to both create and maintain on large tables. The advantage is that the query is not dynamic.
This is because value in the sportEvent string which you are passing as a parameter is not matching with actual column existing in your database table.
Make sure that both of them matches and then only this error will go.
Otherwise dont pass table's column name as a parameter, directly write it in the query and let its column value be a parameter.
Hope it helps.
Is there any way how to do that? This does not work:
SqlCommand command = new SqlCommand("SELECT #slot FROM Users WHERE name=#name; ");
prikaz.Parameters.AddWithValue("name", name);
prikaz.Parameters.AddWithValue("slot", slot);
The only thing I can think of is to use SP and declare and set the variable for the column. Seems to me a bit ackward.
As has been mentioned, you cannot parameterise the fundamental query, so you will have to build the query itself at runtime. You should white-list the input of this, to prevent injection attacks, but fundamentally:
// TODO: verify that "slot" is an approved/expected value
SqlCommand command = new SqlCommand("SELECT [" + slot +
"] FROM Users WHERE name=#name; ")
prikaz.Parameters.AddWithValue("name", name);
This way #name is still parameterised etc.
You cannot do this in regular SQL - if you must have configurable column names (or table name, for that matter), you must use dynamic SQL - there is no other way to achieve this.
string sqlCommandStatement =
string.Format("SELECT {0} FROM dbo.Users WHERE name=#name", "slot");
and then use the sp_executesql stored proc in SQL Server to execute that SQL command (and specify the other parameters as needed).
Dynamic SQL has its pros and cons - read the ultimate article on The Curse and Blessings of Dynamic SQL expertly written by SQL Server MVP Erland Sommarskog.
Does passing SQL Parameters to a stored procedure alone ensure that SQL injection won't happen or the type checks also need to be performed?
As an example -
ADO.NET Code:
Database DBObject = DataAccess.DAL.GetDataBase();
DbCommand command = DBObject.GetStoredProcCommand("usp_UpdateDatabase");
List<DbParameter> parameters = new List<DbParameter>();
parameters.Add(new SqlParameter("#DbName", txtName.Text));
parameters.Add(new SqlParameter("#DbDesc", txtDesc.Text));
command.Parameters.AddRange(parameters.ToArray());
rowsAffected = DBObject.ExecuteNonQuery(command);
SP:
ALTER PROCEDURE [dbo].[usp_GetSearchResults]
-- Add the parameters for the stored procedure here
#DbName NVARCHAR(50) = ''
,#DbDesc NVARCHAR(50) = ''
AS
BEGIN
SET NOCOUNT ON;
SELECT [RegionName]
,[AppName]
FROM [ApplicationComponent]
WHERE [DBName] LIKE ('%' + #DbName+ '%')
OR [DBDesc] LIKE ('%' + #DbDesc+ '%')
END
In the above code, I havent mentioned any parameter types or validation logic. Would it still preevnt SQL injection?
Thanks for the guidance!
No, that should be fine. The value in the LIKE clause is still built up as a string value, rather than being interpreted as part of the SQL statement. It's still being treated as data rather than code, and that's the crucial part of avoiding SQL injection attacks.
Yes, that should still protect you from SQL Injection.
You're not dynamically building the SQL String in your .NET code and you're not using sp_execute to dynamically build and execute a SQL statement in your stored procedure.
Default DbType for an SQLParameter is NVarChar (as per the docs), so this is the type your parameters will have.
Anyway, even if the parameters were of the wrong type, the worst thing you would have would be the type cast exception, not SQL injection.
I would still suggest using typed parameters.
While the implementation catches any injection attempts AS FOR NOW, there is no real guarantee that this will be the case down the line - and hopefully your application will lead a long and prosperous lifetime... =)
With regard to SQL Server, the MSDN article on the subject can be found here:
http://msdn.microsoft.com/en-us/library/ff648339.aspx
I use an API that expects a SQL string. I take a user input, escape it and pass it along to the API. The user input is quite simple. It asks for column values. Like so:
string name = userInput.Value;
Then I construct a SQL query:
string sql = string.Format("SELECT * FROM SOME_TABLE WHERE Name = '{0}'",
name.replace("'", "''"));
Is this safe enough? If it isn't, is there a simple library function that make column values safe:
string sql = string.Format("SELECT * FROM SOME_TABLE WHERE Name = '{0}'",
SqlSafeColumnValue(name));
The API uses SQLServer as the database.
Since using SqlParameter is not an option, just replace ' with '' (that's two single quotes, not one double quote) in the string literals. That's it.
To would-be downvoters: re-read the first line of the question. "Use parameters" was my gut reaction also.
EDIT: yes, I know about SQL injection attacks. If you think this quoting is vulnerable to those, please provide a working counterexample. I think it's not.
I was using dynamic sql (I can hear the firing squad loading their rifles) for search functionality, but it would break whenever a user searched for somebody with a surname like "O'Reilly".
I managed to figure out a work-around (read "hack"):
Created a scalar-valued function in sql that replaced a single quote with two single quotes, effectively escaping the offending single quote, so
"...Surname LIKE '%O'Reilly%' AND..."
becomes
"...Surname LIKE '%O''Reilly%' AND..."
This function gets invoked from within sql whenever I suspect fields could contain a single quote character ie: firstname, lastname.
CREATE FUNCTION [dbo].[fnEscapeSingleQuote]
(#StringToCheck NVARCHAR(MAX))
RETURNS NVARCHAR(MAX)
AS
BEGIN
DECLARE #Result NVARCHAR(MAX)
SELECT #Result = REPLACE(#StringToCheck, CHAR(39), CHAR(39) + CHAR(39))
RETURN #Result
END
Not very elegant or efficient, but it works when you're in a pinch.
One may wish to replace ' with '' instead of parameterizing when needing to address the ' problem in a large amount of ad hoc sql in a short time with minimal risk of breakage and minimal testing.
SqlCommand and Entity Framework use exec sp_executesql....
So there really is an alternative to raw strings with your own escaping pattern presumably. With SqlCommand you are technically using parameterised queries but you're bypassing the ADO.Net abstraction of the underlying SQL code.
So while your code doesn't prevent SQL Injection, the ultimate answer is sp_executesql not SqlCommand.
Having said that, I'm sure there are special handling requirements for generating an SQL Injection-proof string which utilizes sp_executesql.
see: How to return values from a dynamic SQL Stored Procedure to the Entity Framework?
Simple:
const string sql = "SELECT * FROM SOME_TABLE WHERE Name = #name";
and add the #name parameter with value:
cmd.CommandText = sql;
cmd.Parameters.AddWithValue("#name", name);
If you need to escape a string for a MSSQL query try this:
System.Security.SecurityElement.Escape(Value)