In both queries 1 and 2, the text from the textbox is inserted into the database. What's the significance of the parameterized query here?
Passing txtTagNumber as a query parameter
SqlCommand cmd = new SqlCommand("INSERT INTO dbo.Cars " +"VALUES(#TagNbr);" , conn);
cmd.Parameters.Add("#TagNbr", SqlDbType.Int);
cmd.Parameters["#TagNbr"].Value = txtTagNumber.Text;
Converting txtTagNumber to an integer before constructing the query
int tagnumber = txtTagNumber.Text.ToInt16(); /* EDITED */
INSERT into Cars values(tagnumber.Text); /* then is it the same? */
Also, here I would use Regular Expression validation to stop insertion of illegal characters.
Parameterized queries do proper substitution of arguments prior to running the SQL query. It completely removes the possibility of "dirty" input changing the meaning of your query. That is, if the input contains SQL, it can't become part of what is executed because the SQL is never injected into the resulting statement.
Imagine a dynamic SQL query
sqlQuery='SELECT * FROM custTable WHERE User=' + Username + ' AND
Pass=' + password
so a simple sql injection would be just to put the Username in as ' OR
1=1-- This would effectively make the sql query:
sqlQuery='SELECT * FROM custTable WHERE User='' OR 1=1-- ' AND PASS='
+ password
This says select all customers where they're username is blank ('') or
1=1, which is a boolean, equating to true. Then it uses -- to comment
out the rest of the query. So this will just print out all the
customer table, or do whatever you want with it, if logging in, it
will log in with the first user's privileges, which can often be the
administrator.
Now parameterized queries do it differently, with code like:
sqlQuery='SELECT * FROM custTable WHERE User=? AND Pass=?'
parameters.add("User", username) parameters.add("Pass", password)
where username and password are variables pointing to the associated
inputted username and password
Now at this point, you may be thinking, this doesn't change anything
at all. Surely you could still just put into the username field
something like Nobody OR 1=1'--, effectively making the query:
sqlQuery='SELECT * FROM custTable WHERE User=Nobody OR 1=1'-- AND
Pass=?'
And this would seem like a valid argument. But, you would be wrong.
The way parameterized queries work, is that the sqlQuery is sent as a
query, and the database knows exactly what this query will do, and
only then will it insert the username and passwords merely as values.
This means they cannot effect the query, because the database already
knows what the query will do. So in this case it would look for a
username of "Nobody OR 1=1'--" and a blank password, which should come
up false.
Source: lavamunky.com; Nov 2011
SQL injection happens when a possible parameter has SQL within it and the strings are not handled as it should be
eg:
var sqlquerywithoutcommand = "select * from mytable where rowname = '" + condition+''";
and the condition is a string coming from the user in the request. If condition is malicious
say eg:
var sqlquerywithoutcommand = "select * from mytable where rowname = '" + "a' ;drop table mytable where '1=1"+"'";
you could end up running malicious scripts.
However, using parameters the input will be cleaned of any characters which might escape string characters, which means you can be ensured no matter what comes in it will not be able to run inject scripts.
Using the command object with parameters the SQL actually executed would look like this:
select * from mytable where rowname = 'a'';drop table mytable where 1=1'''
in essence it will be looking for a row with rowname = a';drop table mytable where 1=1'
and not running the remaining script.
Parameterized queries handles everything - why go to the trouble?
With parametrized queries, in addition to general injection, you get all the data types handled, numbers (int and float), strings (with embedded quotes), dates and times (no formatting problems or localization issues when .ToString() is not called with the invariant culture and your client moves to a machine with and unexpected date format).
Parameterized queries allow the client to pass the data separately form the query text.
Where on most free from text you would do validation + escaping.
Of course Parameterization don't help against other kind of injection, but as the parameter are passed separately, they are not use as execution text query.
A good analogy would be the "recent" execution bit used with most of the modern processor and Operating system to protect from buffer overflow. It still allows the buffer overflow but prevent the execution of the injected data.
It is quite understandable why one would feel so.
sqlQuery = "select * from users where username='+username+';"
vs
sqlQuery = "select * from users where username=#username;"
Both the above queries seem to do the same thing.But they actually don't.
The former uses input to for a query, the latter decides on the query but only substitutes the inputs as it is during the execution of the query.
To be more clear, the parameters' values are located some where on the stack where the variables' memory is stored and is used for search when needed.
So if we were to give ' OR '1'='1 as the input in username, the former would dynamically construct a new queries or queries as part of the sql query string sqlQuery which is then executed.
While on the same input, latter would search for ' OR '1'=' in the username field of the users table with the statically specified query in the query string sqlQuery
Just to consolidate it, this is how you use parameters to make query:
SqlCommand command = new SqlCommand(sqlQuery,yourSqlConnection);
SqlParameter parameter = new SqlParameter();
parameter.ParameterName = "#username";
parameter.Value = "xyz";
command.Parameters.Add(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:
How can I add user-supplied input to an SQL statement?
(2 answers)
Closed 7 years ago.
I have to program an application management system for my OJT company. The front end will be done in C# and the back end in SQL.
Now I have never done a project of this scope before; in school we had only basic lessons about SQL. Somehow our teacher completely failed to discuss SQL injections, something which I have only now come in contact with by reading about it on the net.
So anyway my question is: how do you prevent SQL injections in C#? I vaguely think that it can be done by properly masking the text fields of the application so that it only accepts input in a specified format. For example: an e-mail textbox should be of the format "example#examplecompany.tld". Would this approach be sufficient? Or does .NET have pre-defined methods that handle stuff like this? Can I apply a filter to a textbox so it only accepts email-address format or a name textbox so it doesn't accept special chars?
By using the SqlCommand and its child collection of parameters all the pain of checking for sql injection is taken away from you and will be handled by these classes.
Here is an example, taken from one of the articles above:
private static void UpdateDemographics(Int32 customerID,
string demoXml, string connectionString)
{
// Update the demographics for a store, which is stored
// in an xml column.
string commandText = "UPDATE Sales.Store SET Demographics = #demographics "
+ "WHERE CustomerID = #ID;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(commandText, connection);
command.Parameters.Add("#ID", SqlDbType.Int);
command.Parameters["#ID"].Value = customerID;
// Use AddWithValue to assign Demographics.
// SQL Server will implicitly convert strings into XML.
command.Parameters.AddWithValue("#demographics", demoXml);
try
{
connection.Open();
Int32 rowsAffected = command.ExecuteNonQuery();
Console.WriteLine("RowsAffected: {0}", rowsAffected);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
My answer is quite easy:
Use Entity Framework for communication between C# and your SQL database. That will make parameterized SQL strings that isn't vulnerable to SQL injection.
As a bonus, it's very easy to work with as well.
SQL injection can be a tricky problem but there are ways around it. Your risk is reduced your risk simply by using an ORM like Linq2Entities, Linq2SQL, NHibrenate. However you can have SQL injection problems even with them.
The main thing with SQL injection is user controlled input (as is with XSS). In the most simple example if you have a login form (I hope you never have one that just does this) that takes a username and password.
SELECT * FROM Users WHERE Username = '" + username + "' AND password = '" + password + "'"
If a user were to input the following for the username Admin' -- the SQL Statement would look like this when executing against the database.
SELECT * FROM Users WHERE Username = 'Admin' --' AND password = ''
In this simple case using a paramaterized query (which is what an ORM does) would remove your risk. You also have a the issue of a lesser known SQL injection attack vector and that's with stored procedures. In this case even if you use a paramaterized query or an ORM you would still have a SQL injection problem. Stored procedures can contain execute commands, and those commands themselves may be suceptable to SQL injection attacks.
CREATE PROCEDURE SP_GetLogin #username varchar(100), #password varchar(100) AS
DECLARE #sql nvarchar(4000)
SELECT #sql = ' SELECT * FROM users' +
' FROM Product Where username = ''' + #username + ''' AND password = '''+#password+''''
EXECUTE sp_executesql #sql
So this example would have the same SQL injection problem as the previous one even if you use paramaterized queries or an ORM. And although the example seems silly you'd be surprised as to how often something like this is written.
My recommendations would be to use an ORM to immediately reduce your chances of having a SQL injection problem, and then learn to spot code and stored procedures which can have the problem and work to fix them. I don't recommend using ADO.NET (SqlClient, SqlCommand etc...) directly unless you have to, not because it's somehow not safe to use it with parameters but because it's that much easier to get lazy and just start writing a SQL query using strings and just ignoring the parameters. ORMS do a great job of forcing you to use parameters because it's just what they do.
Next Visit the OWASP site on SQL injection https://www.owasp.org/index.php/SQL_Injection and use the SQL injection cheat sheet to make sure you can spot and take out any issues that will arise in your code. https://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet finally I would say put in place a good code review between you and other developers at your company where you can review each others code for things like SQL injection and XSS. A lot of times programmers miss this stuff because they're trying to rush out some feature and don't spend too much time on reviewing their code.
SQL injection should not be prevented by trying to validate your input; instead, that input should be properly escaped before being passed to the database.
How to escape input totally depends on what technology you are using to interface with the database. In most cases and unless you are writing bare SQL (which you should avoid as hard as you can) it will be taken care of automatically by the framework so you get bulletproof protection for free.
You should explore this question further after you have decided exactly what your interfacing technology will be.
This question already has answers here:
How can I add user-supplied input to an SQL statement?
(2 answers)
Closed 7 years ago.
I have to program an application management system for my OJT company. The front end will be done in C# and the back end in SQL.
Now I have never done a project of this scope before; in school we had only basic lessons about SQL. Somehow our teacher completely failed to discuss SQL injections, something which I have only now come in contact with by reading about it on the net.
So anyway my question is: how do you prevent SQL injections in C#? I vaguely think that it can be done by properly masking the text fields of the application so that it only accepts input in a specified format. For example: an e-mail textbox should be of the format "example#examplecompany.tld". Would this approach be sufficient? Or does .NET have pre-defined methods that handle stuff like this? Can I apply a filter to a textbox so it only accepts email-address format or a name textbox so it doesn't accept special chars?
By using the SqlCommand and its child collection of parameters all the pain of checking for sql injection is taken away from you and will be handled by these classes.
Here is an example, taken from one of the articles above:
private static void UpdateDemographics(Int32 customerID,
string demoXml, string connectionString)
{
// Update the demographics for a store, which is stored
// in an xml column.
string commandText = "UPDATE Sales.Store SET Demographics = #demographics "
+ "WHERE CustomerID = #ID;";
using (SqlConnection connection = new SqlConnection(connectionString))
{
SqlCommand command = new SqlCommand(commandText, connection);
command.Parameters.Add("#ID", SqlDbType.Int);
command.Parameters["#ID"].Value = customerID;
// Use AddWithValue to assign Demographics.
// SQL Server will implicitly convert strings into XML.
command.Parameters.AddWithValue("#demographics", demoXml);
try
{
connection.Open();
Int32 rowsAffected = command.ExecuteNonQuery();
Console.WriteLine("RowsAffected: {0}", rowsAffected);
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
}
}
My answer is quite easy:
Use Entity Framework for communication between C# and your SQL database. That will make parameterized SQL strings that isn't vulnerable to SQL injection.
As a bonus, it's very easy to work with as well.
SQL injection can be a tricky problem but there are ways around it. Your risk is reduced your risk simply by using an ORM like Linq2Entities, Linq2SQL, NHibrenate. However you can have SQL injection problems even with them.
The main thing with SQL injection is user controlled input (as is with XSS). In the most simple example if you have a login form (I hope you never have one that just does this) that takes a username and password.
SELECT * FROM Users WHERE Username = '" + username + "' AND password = '" + password + "'"
If a user were to input the following for the username Admin' -- the SQL Statement would look like this when executing against the database.
SELECT * FROM Users WHERE Username = 'Admin' --' AND password = ''
In this simple case using a paramaterized query (which is what an ORM does) would remove your risk. You also have a the issue of a lesser known SQL injection attack vector and that's with stored procedures. In this case even if you use a paramaterized query or an ORM you would still have a SQL injection problem. Stored procedures can contain execute commands, and those commands themselves may be suceptable to SQL injection attacks.
CREATE PROCEDURE SP_GetLogin #username varchar(100), #password varchar(100) AS
DECLARE #sql nvarchar(4000)
SELECT #sql = ' SELECT * FROM users' +
' FROM Product Where username = ''' + #username + ''' AND password = '''+#password+''''
EXECUTE sp_executesql #sql
So this example would have the same SQL injection problem as the previous one even if you use paramaterized queries or an ORM. And although the example seems silly you'd be surprised as to how often something like this is written.
My recommendations would be to use an ORM to immediately reduce your chances of having a SQL injection problem, and then learn to spot code and stored procedures which can have the problem and work to fix them. I don't recommend using ADO.NET (SqlClient, SqlCommand etc...) directly unless you have to, not because it's somehow not safe to use it with parameters but because it's that much easier to get lazy and just start writing a SQL query using strings and just ignoring the parameters. ORMS do a great job of forcing you to use parameters because it's just what they do.
Next Visit the OWASP site on SQL injection https://www.owasp.org/index.php/SQL_Injection and use the SQL injection cheat sheet to make sure you can spot and take out any issues that will arise in your code. https://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet finally I would say put in place a good code review between you and other developers at your company where you can review each others code for things like SQL injection and XSS. A lot of times programmers miss this stuff because they're trying to rush out some feature and don't spend too much time on reviewing their code.
SQL injection should not be prevented by trying to validate your input; instead, that input should be properly escaped before being passed to the database.
How to escape input totally depends on what technology you are using to interface with the database. In most cases and unless you are writing bare SQL (which you should avoid as hard as you can) it will be taken care of automatically by the framework so you get bulletproof protection for free.
You should explore this question further after you have decided exactly what your interfacing technology will be.
Does it make sense to prevent sql injection for a create statement? How could I do this?
I wanted to use command parameters, but it doesn't seam to work:
Example:
var createSql = "CREATE TABLE #TableName (#Column1 ...)";
var command = new SqlCommand();
command.CommandText = createSql;
command.Parameters.AddWithValue("#TableName", "XYZ");
command.Parameters.AddWithValue("#Column1", "Col");
// somewhere else
command.Connection = connection;
command.ExecuteNonReader(); // --> exception: invalid syntax at #TableName
Edit: The Column and TableNames are generated depending on other data. Indirectly also on userinput, yes. The given create statement is incomplete. It is just an example.
My problem is, that it seems that the command parameters are not replaced.
You cannot use bind variables for table or column names.
So you'll have to construct that SQL statement using string concatenation and if necessary, manual quoting/escaping, and be very careful how you go about it.
Direct user input would be very dangerous, but if it is only indirectly, for example just choosing options for auto-generated names, you should be okay.
in this specific code there can't be sql injection because the user doesn't have a say in this.
sql injection are caused when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and unexpectedly executed
in your case the user doesn't input anything so there is no worry.
however, your create table query is invalid. you can read here on create statement.
you can't use the "..." in a create statement, and every column must have a type
This question is merely for educational purposes, as I'm not currently building any application that builds SQL queries with user input.
That said, I know that in ADO.NET you can prevent SQL Injection by doing something like this:
OleDbCommand command = new OleDbCommand("SELECT * FROM Table WHERE Account = #2", connection);
command.Parameters.AddWithValue("#2", "ABC");
But assuming that your application is designed in such a way that the user can actually enter the name of the table, can you do the following? (I don't care if it's a bad idea to allow the users to supply the name of the table, I just want to know if the following is possible...)
OleDbCommand command = new OleDbCommand("SELECT * FROM #1 WHERE Account = #2", connection);
command.Parameters.AddWithValue("#1", "Table");
command.Parameters.AddWithValue("#2", "ABC");
I keep getting an exception when I run the second code, saying that the SQL query is incomplete, and I was wondering if the problem is that what I am trying to do simply cannot be done or if I am overlooking something.
No, a query parameter can substitue for one scalar value in your SQL statement.
For example, a single string literal, a date literal, or a numeric literal.
It doesn't have to be in the WHERE clause. Anywhere you can have an expression in SQL, you can include a scalar value, and therefore a parameter. For example, in join conditions, or in the select-list, or in ORDER BY or GROUP BY clauses.
You cannot use query parameters for:
Table identifiers
Column identifiers
SQL keywords
SQL expressions
Lists of values (for example in an IN() predicate)
If you need to make any of these parts of your query user-definable, then you need to build the SQL query string by interpolating or concatenating application variables into the string. This makes it difficult to defend against SQL injection.
The best defense in that case is to whitelist specific values that are safe to interpolate into your SQL string, for instance a set of table names that you define in your code. Let the user choose a table from these pre-approved values, but don't use their input verbatim in SQL code that you then execute.
User input may provide values, but should never provide code.
You may find my presentation SQL Injection Myths and Fallacies helpful. I cover whitelisting in that presentation (my examples are in PHP, but the idea applies to any programming language).