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
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
I'm trying to replace parameters in a string to execute in an Npgsql query.
The problem is, when it replaces the parameter by its value in the string it adds unnecessary parentheses and so the query returns an error.
NAME_SCHEMA_DB and NAME_ADMIN_DB are string constants and
ExecuteCommand just takes an NpgsqlCommand and executes it.
This is my code:
String qdropSchema = #"DROP SCHEMA IF EXISTS #name_schem CASCADE";
String qCreateSchema = #"CREATE SCHEMA #name_schem AUTHORIZATION #name_admin";
DbCommand commandeDrop = new NpgsqlCommand(qdropSchema);
commandDrop.Parameters.Add(new NpgsqlParameter("#name_schem", NAME_SCHEMA_DB));
DbCommand commandCreate = new NpgsqlCommand(qCreateSchema);
commandCreate.Parameters.Add(new NpgsqlParameter("#name_schem", NAME_SCHEMA_DB));
commandCreate.Parameters.Add(new NpgsqlParameter("#name_admin", NAME_ADMIN_DB));
ExecuteCommand(commandDrop);
ExecuteCommand(commandCreate);
This is what the SQL query it tries to run when it reaches ExecuteCommand(commandDrop)
DROP SCHEMA IF EXISTS (('test_schemaName')) CASCADE;
I 'm not sure why it adds the extra parentheses and single quotes. Normally, I'd want the query it runs to be
DROP SCHEMA IF EXISTS test_schemaName CASCADE;
SQL parameters are generally only valid for values (e.g. the values of fields) - not field names and table names etc. While it's annoying, you'll probably need to embed these names directly into the SQL.
You should be very careful doing that, of course - anywhere that it might be from user input, you should use a whitelist of some form.
I have the following code:
string strTruncateTable = "TRUNCATE TABLE #TableNameTruncate";
SqlCommand truncateTable = new SqlCommand(strTruncateTable, myConnection);
truncateTable.Parameters.AddWithValue("TableNameTruncate", tbTableName.Text);
truncateTable.ExecuteNonQuery();
Whenever I run the application, I get the following error:
Incorrect syntax near '#TableNameTruncate'
How can I fix the issue?
How can I fix the issue?
By specifying the table name as part of the SQL. Table and column names can't be parameterized in most database SQL dialects, including SQL Server.
You should either perform very stringent 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 in the normal way.
You can only parameterized your values, not your column names or table names no matter you use DML statements or DDL statements.
And by the way, parameters are supported for Data manipulation language operations not Data Manipulation language operations.
Data manipulation language =
SELECT ... FROM ... WHERE ...
INSERT INTO ... VALUES ...
UPDATE ... SET ... WHERE ...
DELETE FROM ... WHERE ...
TRUNCATE TABLE is a Data Definition Language statement. That's why you can't use TRUNCATE TABLE with parameters even only if you try to parameter a value. You need to specify it as a part of SQL query.
You might need to take a look at the term called Dynamic SQL
As mentioned by Jon Skeet, table name cannot be parametrized for truncate operation.
To fix this issue, fully qualified query needed to be written.
So you can put a conditional check by the parameter value #TableNameTruncate and using if or switch case statement create fully qualified query then execute it.
or simply
string strTruncateTable = "TRUNCATE TABLE " + TableNameTruncate.Value;
SqlCommand truncateTable = new SqlCommand(strTruncateTable, myConnection);
truncateTable.Parameters.AddWithValue("TableNameTruncate", tbTableName.Text);
truncateTable.ExecuteNonQuery();
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).
public static bool TruncateTable(string dbAlias, string tableName)
{
string sqlStatement = string.Format("TRUNCATE TABLE {0}", tableName);
return ExecuteNonQuery(dbAlias, sqlStatement) > 0;
}
The most common recommendation to fight SQL injection is to use an SQL query parameter (several people on this thread have suggested it).
This is the wrong answer in this case. You can't use an SQL query parameter for a table name in a DDL statement.
SQL query parameters can be used only in place of a literal value in an SQL expression. This is standard in every implementation of SQL.
My recommendation for protecting against SQL injection when you have a table name is to validate the input string against a list of known table names.
You can get a list of valid table names from the INFORMATION_SCHEMA:
SELECT table_name
FROM INFORMATION_SCHEMA.Tables
WHERE table_type = 'BASE TABLE'
AND table_name = #tableName
Now you can pass your input variable to this query as an SQL parameter. If the query returns no rows, you know that the input is not valid to use as a table. If the query returns a row, it matched, so you have more assurance you can use it safely.
You could also validate the table name against a list of specific tables you define as okay for your app to truncate, as #John Buchanan suggests.
Even after validating that tableName exists as a table name in your RDBMS, I would also suggest delimiting the table name, just in case you use table names with spaces or special characters. In Microsoft SQL Server, the default identifier delimiters are square brackets:
string sqlStatement = string.Format("TRUNCATE TABLE [{0}]", tableName);
Now you're only at risk for SQL injection if tableName matches a real table, and you actually use square brackets in the names of your tables!
As far as I know, you can't use parameterized queries to perform DDL statements/ specify table names, at least not in Oracle or Sql Server. What I would do, if I had to have a crazy TruncateTable function, that had to be safe from sql injection would be to make a stored procedure that checks that the input is a table that is safe to truncate.
-- Sql Server specific!
CREATE TABLE TruncableTables (TableName varchar(50))
Insert into TruncableTables values ('MyTable')
go
CREATE PROCEDURE MyTrunc #tableName varchar(50)
AS
BEGIN
declare #IsValidTable int
declare #SqlString nvarchar(50)
select #IsValidTable = Count(*) from TruncableTables where TableName = #tableName
if #IsValidTable > 0
begin
select #SqlString = 'truncate table ' + #tableName
EXECUTE sp_executesql #SqlString
end
END
If you're allowing user-defined input to creep into this function via the tablename variable, I don't think SQL Injection is your only problem.
A better option would be to run this command via its own secure connection and give it no SELECT rights at all. All TRUNCATE needs to run is the ALTER TABLE permission. If you're on SQL 2005 upwards, you could also try using a stored procedure with EXECUTE AS inside.
CREATE OR REPLACE PROCEDURE truncate(ptbl_name IN VARCHAR2) IS
stmt VARCHAR2(100);
BEGIN
stmt := 'TRUNCATE TABLE '||DBMS_ASSERT.SIMPLE_SQL_NAME(ptbl_name);
dbms_output.put_line('<'||stmt||'>');
EXECUTE IMMEDIATE stmt;
END;
Use a stored procedure. Any decent db library (MS Enterprise Library is what I use) will handle escaping string parameters correctly.
Also, re:parameterized queries: I prefer to NOT have to redeploy my app to fix a db issue. Storing queries as literal strings in your source increases maintenance complexity.
Have a look at this link
Does this code prevent SQL injection?
Remove the unwanted from the tableName string.
I do not think you can use param query for a table name.
There are some other posts which will help with the SQL injection, so I'll upvote those, but another thing to consider is how you will be handling permissions for this. If you're granting users db+owner or db_ddladmin roles so that they can truncate tables then simply avoiding standard SQL injection attacks isn't sufficient. A hacker can send in other table names which might be valid, but which you wouldn't want truncated.
If you're giving ALTER TABLE permissions to the users on the specific tables that you will allow to be truncated then you're in a bit better shape, but it's still more than I like to allow in a normal environment.
Usually TRUNCATE TABLE isn't used in normal day-to-day application use. It's used for ETL scenarios or during database maintenance. The only situation where I might imagine it would be used in a front-facing application would be if you allowed users to load a table which is specific for that user for loading purposes, but even then I would probably use a different solution.
Of course, without knowing the specifics around why you're using it, I can't categorically say that you should redesign, but if I got a request for this as a DBA I'd be asking the developer a lot of questions.
Use parameterized queries.
In this concrete example you need protection from SQL injection only if table name comes from external source.
Why would you ever allow this to happen?
If you are allowing some external entity (end user, other system, what?)
to name a table to be dropped, why won't you just give them admin rights.
If you are creating and removing tables to provide some functionality for end user,
don't let them provide names for database objects directly.
Apart from SQL injection, you'll have problems with name clashes etc.
Instead generate real table names yourself (e.g DYNTABLE_00001, DYNTABLE_00002, ...) and keep a table that connects them to the names provided by user.
Some notes on generating dynamic SQL for DDL operations:
In most RDBMS-s you'll have to use dynamic SQL and insert table names as text.
Be extra careful.
Use quoted identifiers ([] in MS SQL Server, "" in all ANSI compliant RDBMS).
This will make avoiding errors caused by invalid names easier.
Do it in stored procedures and check if all referenced objects are valid.
Do not do anything irreversible. E.g. don't drop tables automatically.
You can flag them to be dropped and e-mail your DBA.
She'll drop them after the backup.
Avoid it if you can. If you can't, do what you can to minimize rights to other
(non-dynamic) tables that normal users will have.
You could use SQLParameter to pass in tableName value. As far as I know and tested, SQLParameter takes care of all parameter checking and thus disables possibility of injection.
If you can't use parameterized queries (and you should) ... a simple replace of all instances of ' with '' should work.
string sqlStatement = string.Format("TRUNCATE TABLE {0}", tableName.Replace("'", "''"));