I'm trying to get the following code to work:
String connStr = sqlRoutines.connectionString;
SqlConnection sqlConn = new SqlConnection(connStr);
sqlConn.Open();
SqlCommand cmd = new SqlCommand();
cmd.Connection = sqlConn;
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT * FROM TABEL=#tabel";
cmd.Parameters.Add("#tabel", SqlDbType.Text).Value = DataContainer.sqlTabel;
SqlDataReader reader = cmd.ExecuteReader();
Console.WriteLine(reader.FieldCount.ToString());
reader.Close();
sqlConn.Close();
Somehow the value "DataContainer.sqlTabel" is not added to the command. Am I missing something here?
Whenever I use cmd.CommandText = "SELECT * FROM" + DataContainer.sqlTabel; everything is working fine. However I want to avoid this method because of the SQL Injection.
Thanks in advance!
EDIT:
I want to achieve a command that uses a variable (which is changed by the user). So I want to have something like this: SELECT * FROM * a variable defined by the use *;. When I use:
cmd.CommandText = "SELECT * FROM #tablename";
cmd.Parameters.Add("#tablename", SqlDbType.Text).Value = DataContainer.sqlTabel;
It doesn't work as well.
I think you try to parameterize table name which you can't. I don't understand what is TABEL either. FROM (Transact-SQL) doesn't have a syntax like that.
You can only parameterize values. Not table names or column names. Specify the table name as part of the SQL. But when you do that, you need very strong validation on the table name before putting it into the SQL, or have a whitelisted set of valid table names, in order to avoid SQL injection attacks.
If you really want to parameterize it, you can use (but not recommended) Dynamic SQL.
SELECT * FROM #tablename
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.
Also use using statement to dispose your database connections.
using(SqlConnection sqlConn = new SqlConnection(connStr))
using(SqlCommand cmd = sqlConn.CreateCommand())
{
...
...
using(SqlDataReader reader = cmd.ExecuteReader())
{
...
}
}
You can't do this. You can only use dynamic SQL. You need to decide for yourself whether SQL injection is a risk and if so you need to code for this, perhaps checking that the value of table doesn't contain anything other than a valid table name. You can check the table name against the system tables to ensure it is valid.
we can't use parameters for either table name or column name. parameters only limited for values. if you want to use parameter for table name then you've to create a stored procedure and then pass the table name as parameter to store procedure. more information can be found here
Table name as parameter
Related
I have a situation where I have to take input from a user, create a SQL command and send that command to a service that will execute the SQL. The service ONLY allows for a SQL string -- not additional parameters; so I am forced to create the entire SQL statement on my end of things.
I do not have any kind of access to the database itself -- only a service that sits overtop of it.
I realize the following is NOT safe:
var sql = $"SELECT * FROM tablename WHERE name = '{incomingdata.searchName}'";
But if I generate SQL with parameters, would this be safe from SQL injection?
var sql = $#"
DECLARE #Name varchar(50);
SET #Name = '{incomingdata.searchName}';
SELECT * FROM tablename WHERE name = #Name";
This is not an ideal situation. I would try and look for a parametrized way to solve this problem failing that I would test the input and in ANY case where a test fails not allow the query at all and ask the user to re-enter.
Do the following tests:
Length of input is smaller than a max name size (25 characters?)
All input characters are in the alphabet
No reserved SQL words (easy to find with a google search)
If the input does not fail any of these tests you should be OK. DON'T try to sanitize the input -- this can be hard/impossible to do with international character sets.
Disclosure: My background is C++, Java and TypeScript/JavaScript, not C#
Would this be more appropriate:
SqlCommand sql = new SqlCommand("SELECT * FROM tablename WHERE name = #Name");
sql.Parameters.Add("#Name", SqlDbType.VarChar, 50).Value = incomingdata.searchName);
Sanitizing the user data before it gets to this stage, using a trusted package, might also be helpful.
The second example is better, but still not fully secure.
SQL injection attacks can still occur if the input data is maliciously crafted, regardless of whether the input data is directly embedded into the string or used as a parameter.
A more secure way to handle this situation is to use parameterized queries, which automatically escape any special characters in the input data and prevent SQL injection attacks.
Unfortunately, if the service you are using only accepts raw SQL strings and does not support parameters, your options are limited. In this case, it is recommended to validate and sanitize the input data before constructing the SQL string to minimize the risk of SQL injection.
To make the SQL statement safe from SQL injection, you can use parameterized queries. In .NET, you can use the SqlCommand.Parameters property to define parameters and their values. The following is an example:
using (SqlConnection connection = new SqlConnection(connectionString))
{
connection.Open();
string sql = "SELECT * FROM tablename WHERE name = #Name";
using (SqlCommand command = new SqlCommand(sql, connection))
{
command.Parameters.AddWithValue("#Name", incomingdata.searchName);
using (SqlDataReader reader = command.ExecuteReader())
{
// process the results
}
}
}
In this example, the value of incomingdata.searchName is passed as a separate parameter and not directly concatenated into the SQL string. This protects against SQL injection because the parameter value is automatically escaped and properly formatted by the .NET framework.
You are along the right lines. You never want to use a variable that can be changed. Instead, you need to use SQL parameters. You can add a SQL parameter like this:
command.Parameters.Add(new SqlParameter("#Name", "incomingdata.searchName"));
And then refer to it in your query like this:
SELECT *
FROM tablename
WHERE name = #Name";
Once this is done, when a user tries to change the value of a variable the query will return no results. It should be said that this way of doing it does result in the SQL property assuming the type of the C# variable. There are other ways of doing this if you want to specify the type of the property to be different from the variables type. This is a useful resource https://jonathancrozier.com/blog/preventing-sql-injection-in-c-sharp-applications
This question already has answers here:
When should I use prepared statements?
(4 answers)
Closed 1 year ago.
I have code that inputs data into db using OLEDB. Let's say it looks like this
var commandText = $"INSERT into {tableName}
({columnName1}, {columnName2})
VALUES ({value1, value2});"
var command = new OleDbCommand(commandText, connection);
command.ExecuteNonQuery();
Suggestion is to use OLEDB parameters, something like this
var commandText = $"INSERT into {tableName}
([{columnName1}], [{columnName2}])
VALUES (?, ?);"
var command = new OleDbCommand(commandText, connection);
command.Parameters.Add(new OleDbParameter(columnName1, value1));
command.Parameters.Add(new OleDbParameter(columnName2, value2));
command.ExecuteNonQuery();
What are the benefits of using parameters here?
Does it really improve security if the values are validated before?
With this code, no amount of parameters can help you.
The fact that you're concatenating the table name and the columns names makes your query vulnerable to SQL Injection attacks, which is the primary (but not only) reason to use parameters.
The way SQL injection works is by replacing parts of the string sent to the database with sql code. Parameters prevent that from happening because the database treats them as placeholders for data, which means it will not run any sql code that was passed through them.
However, since your table name and column names are also c# variables, they can be replaced with SQL code that the database will try to run.
Suppose the following code:
var tableName = "table (Col1) VALUES (null);DROP TABLE table;--";
// declare and populate columnName1, columnName2 with whatever values you want here, even just nulls
var commandText = $"INSERT into {tableName}
([{columnName1}], [{columnName2}])
VALUES (?, ?);"
// run SQL command here
This will insert a single record into table, and then drop the table from the database.
For more information, read my blog post entitled Back to basics: SQL Injection
Actually, yes. We all make mistakes and the extra safety added by the parameter object is like a second set of eyes.
Also, if you always use the parameter object, you run less of a risk in introducing errors down the line.
I'd like to create a dynamic SQL query with c#'s SqlCommand where even the table is a parameter, so as to avoid injection attempts. Like below:
comm.CommandText = "SELECT * FROM #tbl WHERE cond=#cond";
comm.Parameters.AddWithValue("tbl","TABLENAME");
comm.Parameters.AddWithValue("cond","CONDITION");
However, I have found that this is not allowed. I've looked into using Dynamic SQL with an execute, but that seems to be only for stored procedures. Can I use Dynamic SQL with an Execute using parameters for the table name with an SqlCommand? If not, how can this be done to avoid SQL injection problems?
Thanks!
Use SqlCommandBuilder.QuoteIdentifier method to escape table names.
SqlCommandBuilder builder = new SqlCommandBuilder();
string tableName ="SomeTable";
string escapedTableName = builder.QuoteIdentifier(tableName);
Later you can use the escaped table name in your string like:
comm.CommandText = "SELECT * FROM "+ escapedTableName +" WHERE cond=#cond";
If the name of the table you're selectint from is not user-supplied, there's nothing to worry about.
If, however, you allow dynamic specification of tables to be queried, you'll need the QuoteIdentifier approach suggested by #Habib and I strongly recommend whitelisting all the available table names.
I'm totally new to C#. I am validating username and password with case-sensitive
from database sql server 2008. Here is my login code; what should I do?
SqlConnection conn = new SqlConnection(#"Data Source=.\SQLEXPRESS;Initial Catalog=db_WiBo;Integrated Security=True");
SqlCommand cmd = new SqlCommand("SELECT * from tb_Account where Username= '"+textBox1.Text+"' AND Password= '"+textBox2.Text+"' ", conn);
conn.Open();
SqlDataReader reader = cmd.ExecuteReader()
if (reader.HasRows)
{
reader.Close();
this.Hide();
}
Thanks in advance
1) you should be using stored procedures or parameterised query instead of SQL Concatenation. you are presenting a huge SQL Server injection security flaw in your code already.
what is the problem you are having? code looks fine - are you sure the inputs match the data in the database if there are no records being retrieved?
the code simply executes the query and if found, closes the reader and hides the form.
you should also not store raw passwords in the DB - another security flaw. instead, hash them/encrypt them and check that value against the hashed/encrypted value from the input.
for case sensitivity, you could use Collation
http://technet.microsoft.com/en-us/library/ms184391.aspx
http://blog.sqlauthority.com/2007/04/30/case-sensitive-sql-query-search/
A few things:
You are missing a ';' at the end of SqlDataReader reader = cmd.ExecuteReader().
As was already mentioned, use a Stored Procedure for what you are doing.
As was also mentioned, use parameterized queries since you are accepting input from textboxes.
Use a using statement to manage your connection and command objects.
Don't forget to .Close() your connection when you are done.
Oh, and I almost forgot, hash your passwords!
Here is an example of the above:
using (SqlConnection conn = new SqlConnection(#"Data Source=.\SQLEXPRESS;Initial Catalog=db_WiBo;Integrated Security=True"))
{
using (SqlCommand cmd = new SqlCommand(#"SELECT * from tb_Account where Username= '#username' AND Password= '#password' ", conn))
{
cmd.Parameters.Add("#username", textBox1.Text);
cmd.Parameters.Add("#password", textBox2.Text);
conn.Open();
SqlDataReader reader = cmd.ExecuteReader();
if (reader.HasRows)
{
reader.Close();
this.Hide();
}
conn.Close();
}
}
Other than your SQL injection issues, you need to use a collation or cast to binary. I found another SO question that has a bunch of helpful things:
How to do a case sensitive search in WHERE clause (I'm using SQL Server)?
First of all: Do not use string concat for that. This can easily be used for code injection.
You can use stored procedures instead, or LinQ to SQL or even use the built-in membershipprovider
Notwithstanding the design issues already pointed out with respect to security, if your SQL Server instance's default collation is case-insensitive, you'll need to select a suitable collation. The default collation for a SQL Server installation is [usually, depending on the server locale] SQL_Latin1_General_Cp1_CI_AS, meaning Latin-1 code page, case-insensitive, accent-sensitive.
When you create a database, you can specify a default collation for that database. And when you create a table, you may specify the collation to be used for each char, varchar, nchar or nvarchar column.
You may also change these via appropriate DDL statements. Note that altering the collatino may affect data integrity, causing things like primary keys and unique indices to be broken.
Create a table with and specifying the collation for its columns is easy:
create table account
(
id int not null identity(1,1) primary key clustered ,
user_id varchar(32) collate SQL_Latin1_General_Cp1_CS_AS not null unique ,
password varchar(32) collate SQL_Latin1_General_Cp1_CS_AS not null unique ,
...
)
You may use alter table and alter database to change the collations as well.
Supported collations can be found at http://technet.microsoft.com/en-us/library/ms180175.aspx and http://technet.microsoft.com/en-us/library/ms188046.aspx
You should
Note that mixed collations can cause problems when comparing 2 columns, and
Heed the security issues raised by others.
As a reaction to MySqlParameter as TableName, it seems that MySQL's Connector/NET library doesn't support table names from user input in the following way:
MySqlCommand cmd = new MySqlCommand("SELECT * FROM #table");
cmd.Parameters.AddWithValue("#table",TableNameFromUserInput);
So I tried to find another way, but I couldn't find any libraries that did this for me.
When searching for how to do this manually, I couldn't found anything that didn't tell you to use "prepared statements" from some already defined library, no matter the language.
To my limited knowledge of SQL, I only think it's necessary to put backticks (`) around the user input and then check the input for backticks - but I wanted to be sure.
Question
How do you protect a user specified table name from SQL-Injection when the MySQL Connector doesn't support it?
Check if
TableNameFromUserInput
is an existing table, before executing the query.
That prevents other errors like "table doesnt exist" aswell.
you cannot add tableName (as well as columnName) as parameter in prepared statements because it only supports for a value. For your safety, add additional code to validate tableName, ex.
string tableName = "hello";
tableName = UDFunctionClean(tableName);
string query = String.Format("SELECT * FROM `{0}`", tableName);
MySqlCommand cmd = new MySqlCommand(query);