I am working on a C# windows form which is connected to MySQL and updates strings within the form. I have everything working properly except for a small issue.
Say you want to update the "notes" field to read "The dog's bone", that apostrophe is causing the SQL query to end and cause an error. How can I get around this please?
UPDATE `database`
SET `notes` = 'The dog's bone'
WHERE `Pet` = 'Dog';
Thanks!
You can escape ' character in MySQL with doubling it like ''.
Other than that, if you use parameterized queries, you will not need this at all. Just pass your The dog's bone string directly to your parameterized query and you will be fine.
Also I strongly suspect you try to use UPDATE instead of SELECT statement. In MySQL, SELECT syntax doesn't have any SET part.
And using a reserved keyword as a column name is a bad idea. As a best practice, change your database column name to non-reserved word.
using(var con = new MySqlConnection(conString))
using(var cmd = con.CreateCommand())
{
cmd.CommandText = #"UPDATE `database` SET notes = #notes
WHERE Pet = #pet";
cmd.Parameters.AddWithValue("#notes", "The dog's bone");
cmd.Parameters.AddWithValue("#pet", "Dog");
con.Open();
cmd.ExecuteNonQuery();
}
I used AddWithValue method as an example in my code since I didn't know your column types but you don't use it. This method may generate unexpected and surprising results sometimes. Use Add method overloads to specify your parameter type and it's size.
Escape it with another single quote ':
SELECT `database`
SET `notes` = 'The dog''s bone'
WHERE `Pet` = 'Dog';
Related
I want to learn how SQLInjection is working with the PostgresqlDb. I am using the Npgsql in C#.
So this is my Query, which is called, when I rename a folder:
cmd.CommandText = "UPDATE allfolder.folder SET folder_name = '" + foldernamenew + "'";
cmd.ExecuteNonQuery();
I now tried to pass the following value into the textfield:
abcdef; INSERT INTO allfolder.folder (id, folder_name) VALUES (56,"aaaaaaa");
Then AJAX is fired.
The output I assumed is, that all folders in the table has the folder_name "abcdef" and that I have a new folder with the id "56" called "aaaaaa". This is not the case, because the semicolon is not recognized as delimiter and so the name of each folder_name are "abcdef; INSERT INTO ....". I do not want to change it on DB side that multiqueries are allowed.
So my questions are:
How do I need to prepare the SQL statement, that I achieve a Injection?
Is an injection even possible, when you are not allowed to execute a second qry because the semicolon isn't recognized?
I am only talking about Npgsql and postgres.
As Laurenz mentioned above, this should work:
abcdef'; INSERT INTO allfolder.folder (id, folder_name) VALUES (56,'aaaaaaa'); -- test
Make sure, that you don't mix single and double quotes. A common mistake in SQL. You need the single quote before the semicolon, otherwise it is in the textstring, because you have no delimiter.
“Multiqueries” (several queries in one line, separated by semicolon) are always allowed in PostgreSQL.
Your problem are the multiple errors in your SQL:
Missing single quote after abcdef.
Double quotes instead of single quotes around aaaaaaa.
No single quote or line comment at the end of the statement.
Speaking pointedly: you have to learn SQL before you can learn SQL injection.
The problem is when user insert non-Latin word to database, if collation not set to that alphabet, the word comes like '?????' But if user insert word like N'word' or I select it like N'word' there is no problem.I use hastable function on C# side so is there any solution for use N'word' format automaticly or must I use N before text everytime I call function?I already use NVARCHAR format by the way.
The simple way to ask;I don't want to use N'word' format every time when I select item from database.Is there any trigger, stored procedure or function for add automaticly N before text I select.
You shouldn't use the N'word' format at all, you should use parameters. When you concatenate values into a string to create a query, it's wide open to SQL injection attacks unless you managage to escape all input exactly right.
Put parameters in the query and add the values to the Parameters collection of the command. Example:
string query = "select Id from Persons where Name = #Name";
using (SqlCommand cmd = new SqlCommand(query, connection)) {
cmd.Parameters.Add('#Name', SqlDbType.NVarChar, 50).value = name;
using (SqlDataReader reader = cmd.ExecuteReader()) {
while (reader.Read()) {
...
}
}
}
Using unicode types like NVarChar for the parameter ensures that the parameter value is sent as unicode, equivalent to the N'word' format.
Why don't you use some sort of ORM. Dapper is a lightweight ORM:
https://github.com/StackExchange/dapper-dot-net
It will solve your problems with parameter passing if this is the troubles you are having
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.
Please help me to store apostrophe. I m creating a website (C#, .net, SQL Server) and want to have a message box for the users but the problem is that when I inserts any message such as John's it shows an error near ''s'.
Please tell me how could I store apostrophe in database
I used nvarchar, varchar and everything but failed to store apostrophe containing messages.
A general solution is to write message with double apostrophe but this is not a solution for a website
You are open for SQL-Injection. Don't concatenate strings to build your query. Instead use SQL-Parameters. That also makes your code more readable and prevents errors like yours.
Here's an example:
int amt;
using (var con = new SqlConnection(ConnectionString)) {
var sql = "INSERT INTO dbo.Message(UserID, Message) VALUES(#UserID, #Message);";
using (var cmd = new SqlCommand(sql, con)) {
cmd.Parameters.AddWithValue("#UserID", userID); // passed as argument
cmd.Parameters.AddWithValue("#Message", txtMessage.Text); // f.e. "John's"
con.Open();
int inserted = cmd.ExecuteNonQuery();
}
}
The same works also with other sql like UPDATE commands.
The problem is that you need to escape Apostrophe by another Apostrophe.
For example have a look at:http://sqlfiddle.com/#!3/d2f75/1
CREATE TABLE tblTEst( col1 NVARCHAR(50))
INSERT INTO tblTest
(Col1)
SELECT 'John''s'
The best solution is to use a prepared statement (or whatever the equivalent in C# is) where your SQL only contains placeholders and you pass the actual values through a different method.
In a character literal, the single quote ' can be used by simply doubling it:
insert into foo (bar)
values
('John''s');
use CHAR(39)between john & s like this: 'john'+CHAR(39)+'s'
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)