I am creating a website in C# (Visual Studio 2010). I have got string values in my database which contain single quotes. I replaced them with double single quotes. But while populating the data into a CheckBoxList, the double single quotes are displayed instead of a single quote.
My query is:
SqlDataSource1.SelectCommand = select column1 from table1 WHERE column1<>'"+var1+"'";
You can escape the quotes using two single quotes like so:
"select column1 from table1 where column1 <> ''"+var1+"''";
But remember you're opening yourself up for SQL injection attack. Use SQL Parameters appropriately.
Instead of storing fudged data in your database and then changing it back on output, you should be escaping the single quotes in your query - for MSSQL, single quotes are escaped by doubling them.
However, you'll get a more secure and faster-running query if you parameterise it and assign the value (which now doesn't need escaping) to a SqlParameter object when you make your connection.
If your var1 is a variable, your code does not surround it double single quotes.
I think the right syntax should be something like;
"select column1 from table1 WHERE column1 <> '" + String.Format("''{0}''", var1) + "'";
But more important, you should always use parameterized queries. This kind of string concatenations are open for SQL Injection attacks.
I stopped storing the single quotes in the database to double single quotes (' '). Instead, as suggested, I used a parameterized query. I stopped using an SqlDataSource.
Code:
SqlCommand cmd=new SqlCommand("select column1 from table1 where column1<>#var1",conn);
cm.Parameters.Add("var1",SqlDbType.VarChar).Value=var1;
rdr=cmd.ExecuteReader();
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.
My C# application is able store the data into a SQL Server database. Currently I have to problem when user insert symbol ' in their string/sentences:
Example: I want to 'test' your system
So, when inserting into db the ' symbol will return an error while inserting by using sql query.
My query example :
INSERT INTO TABLE_NAME (POST_BODY)
VALUES ('i want to 'test' your system')
and then my plan here is to change that check the string if contains that ' symbol it will change to " symbol.
I have try using this code, but cannot:
void ChangeSymbol(String str)
{
Console.WriteLine("\"{0}\"", str);
Console.WriteLine("\"{0}\"", str.Replace(''', '"'));
}
Please anybody help to give some idea to face this problem. Thanks in advance.
There is no problem inserting a single quote into a database using SQL code. If you want to insert a text literal then you simply escape the single quote with another single quote, e.g.
INSERT INTO MyTable (GivenName, FamilyName) VALUES ('James', 'O''Connell')
If you're inserting a separate value into a SQL statement then you should be using parameters no matter the data type, so an issue with single quotes never arises, e.g.
mySqlCommand.CommandText = "INSERT INTO MyTable (GivenName, FamilyName) VALUES (#GivenName, #FamilyName)";
mySqlCommand.Parameters.AddWithValue("#GivenName", givenName);
mySqlCommand.Parameters.AddWithValue("#FamilyName", familyName);
Use parameter binding. I don't have a sample code to put in since we dont use MSSQL
here's a sample
http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters(v=vs.110).aspx
You escape single quotes by doubling them. So try this:
string example = "I want to ''test'' your system";
I have a C# console application that makes a bunch of queries to a database server.
I frequently need to modify the SQL and would like to simply copy/paste the SQL from my SQL Editor into my C# source without having to reformat the SQL every time.
Currently, the SQL is all on one line... like below:
OleDbDataAdapter da_ssm_servers = new OleDbDataAdapter(#"SELECT * FROM mytable ORDER BY Server;", connSSM);
The SQL is much longer than above with a lot of table JOINS, etc.
I would like to keep the formatting, but don't really want to have to go back and add quotes around each line, etc.
If anyone has any recommendations and examples, it would be appreciated.
I do it like this:
string sql = #"
SELECT *
FROM mytable
ORDER BY Server";
OleDbDataAdapter da_ssm_servers = new OleDbDataAdapter(sql, connSSM);
My recommendation would be to stay away from ad hoc queries like you are using and utilize stored procedures. That would decouple your design, as well as limit your calls to a stored procedure name and possibly parameters.
But if you must use ad hoc queries then prefix with # and you will be able to span multiple lines without having to surround each line in quotes.
As long as you use the # syntax then you can have the SQL span multiple lines just fine.
For example
string sql = #"select
colA,
colB,
colC
from
tableX
inner join tableY
on tableX.colA = tableY.colA
where
colB > 20;"
It seems that your code should work fine. When you start your string with # then you're using a verbatim string. Line breaks and formatting are preserved and you don't need to enclose each line in quotes. You just need an ending quote.
I follow the syntax of
INSERT INTO Table1
VALUES (value1, value2, value3…)
This has worked fine so far. But now I have some values that contain normal English text like "I'm going home". The ' character ruins the SQL command in C#. I have written the following:
command.CommandText = "INSERT INTO Bio VALUES ('" + name + "','"I'm going home" + "');
evaluates to
INSERT INTO Bio VALUES ('Peter','I'm going home')
which obviously will not work. How do I make sure special character will not ruin the SQL statements?
Use SqlParameter for heaven's sake. Otherwise your program will be vulnerable to SQL Injection. It will also solve your problem with the special characters.
Learn about parameterized queries for your provider. They exists for Odbc, OleDb, Sql, etc.
command.CommandText = "INSERT INTO Bio Values (#name, #text)";
command.Parameters.Add(/* appropriate param type for your provider */); // add for #name, #text, etc.
// execute query
Use two single quotes whenever there is a single quote you want to escape
Also instead of building your queries like this, you should use parameterized queries in a language of your choice. Escaping the characters yourself opens the door for SQL Injections.
Usually you can escape a single quote by screening with another one.
For example the following is a valid statement
INSERT INTO myTable (Column1) VALUES ('Hello I''m Jack');
However I suggest you using parameters.
command.CommandText = "INSERT INTO Bio VALUES (#Name, #OtherValue)";
command.Parameters.AddWithValue("Name", name);
command.Parameters.AddWithValue("OtherValue", "I'm going home");
One addition point in favor of using parameters is that you are free from burden of formatting and other stuff. I mean date values, uniqueidentifiers, etc.
I do use
HttpUtility.HtmlEncode(text)
It makes all that SQL injection stuff disappear, and it seems easier than to use parameters.
Don't forget to use
HttpUtility.HtmlDecode(text)
to get your input back in the form you received it
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)