I've been looking through the documentation on string formatting in .Net and haven't found this bit yet, and was hoping someone could point me in the right direction. I've come across a working piece of code that takes SqlParameters and puts them in a string like this:
SqlParameter[] arrParams = new SqlParameter[]
{
new SqlParameter("#ClientID", clid),
new SqlParameter("#CustomerID", cuid),
new SqlParameter("#AdminUser", false)
};
string sqlText = string.Format("Insert into [Table1] (RID, CustomerID, AdminUser) values (#ClientID,#CustomerID,#AdminUser)");
..and when running that string down the line in a SqlCommand the proper values are put into the right spots. I'm used to using curly braces for string formatting arguments and not the #symbol and so was wondering where to learn more about this?
This code does not actually need String.Format.
String.Format is for times when you would normally do "string" + variable + "more string". This would be written as String.Format("string{0}morestring", variable); In this case, it is just one string, so that is why there is no need...nothing is being concatenated together.
Here is a good explanation of String.Format
What is happening here is that the #VariableName is being filled with your SqlParameters to avoid SQL Injection. In a nutshell, when you create a SqlParameter, the .NET library looks for either a SQL parameter that matches the name, which could be a stored procedure, function, etc, or any item in a SQL text that begins with # and matches the name.
And here is a good explanation of how SqlParameters work
I think there is some confusion here. The # symbol is used to identify the named SQL parameters within the INSERT INTO statement and not for String.Format.
This is not similar to String.Format what is actually happening is you are running the SQL Command, the command looks for variables called #ClientID,#CustomerID and #AdminUser, which are passed to SQL Server as parameters. You will have something like cmd.Parameters = arrparams a bit further down.
The actual String.Format part around the SQL text is redundant you are right, it will been to use the curly brace route like you suggested.
Hope this helps.
Related
Trying to Insert into database from textboxes, but it will only accept integers and not characters - what could the problem be?
string sCMD = string.Format("INSERT INTO [Table] ([Item], [Des1],[Des2], [Prodline], [ANR], [STime]) VALUES({0},{1},'0',{2},{3},{4})"
,txtText1.Text, txtText2.Text, txText3.Text, txtText4.Text, txtText5.Text);
The name "" is not permitted in this context. Valid expressions are constants, constant expressions, and (in some contexts) variables. Column names are not permitted.
Here's something to consider:
using (SqlConnection c = new SqlConnection(connString))
{
c.Open();
using (SqlCommand cmd = new SqlCommand("INSERT INTO [Table] ([Item], [Des1],[Des2], [Prodline], [ANR], [STime]) VALUES(#Item,#Des1,'0',#ProdLine,#ANR,#STime)", c))
{
cmd.Parameters.AddWithValue("#Item", txtText1.Text);
cmd.Parameters.AddWithValue("#Des1", txtText2.Text);
cmd.Parameters.AddWithValue("#ProdLine", txText3.Text);
cmd.Parameters.AddWithValue("#ANR", txtText4.Text);
cmd.Parameters.AddWithValue("#STime", txtText5.Text);
cmd.ExecuteNonQuery();
}
}
If you were to send the SQL statement you're building to the server it might look something like this:
INSERT INTO [Table] ([Item], [Des1],[Des2], [Prodline], [ANR], [STime])
VALUES(Item Name,Here is my description.,'0',Prod line,ANR value,some time)
Clearly that's going to fail. It's not even surrounding the values with single quotes. Now, all of them may not be character, I get that, but you get my point.
But to add insult to injury it's wide open to SQL Injection the way you have it written. With the parameterized approach it's not.
This is a very dangerous line of code.
For starters, you are creating a string with no delimiters whatsoever for the values, which means that the only values that could pass withour issue are integers. Anything else needs to be delimited, which you don't do in this String.Format statement.
Worse, you are trying to create a sql statement from direct user input. Any weird value can cause your code to fail, or worse, cause execution of unwanted code. Imagine what would happen in a user entered eg 'sdf','sdfs',sdf' as the FIRST value. The resulting string would have 3 correct values for the first three columns that came from the first textboxt.
Now image what would happen if the user entered something like 'blablabla';DROP TABLE sometable;--. This would cause the Delete command to execute. This is a standard SQL injection attack scenario.
There are many more problems, eg when you try to pass numbers with floats, dates or any type whose conversion to string depends on your locale.
Instead of trying to construct a SQL query by string concatenation, you should use parameterized queries, as described in Give me parameterized SQL or give me death. The resulting code is easier to write, performs much faster, has no conversion errors and is not subject to SQL injection attacks,
Currently I simply don't allow apostrophe's at all (along with other character's as you can see) with this, reiterated for each field:
foreach(char c in Comments)
{
if(c=='\'' || c=='$' || c=='\"' || c=='&' || c=='%' || c=='#' || c=='-' || c=='<' || c=='>')
{
errorMessage = "You have entered at least one invalid character in the \"Comments\" field. Invalid characters are: [\'], [\"], [&], [$], [#], [-], [<], [>], and [%]";
}
}
I've been coding this for a while, and I am getting better, but the real problem is that, while I am sure there is a way to effectively "strip-out" or otherwise validate the user input, I am not sure which approach is best and probably wouldn't until a security crisis was imminent.
If I have to, I will settle on simply never allowing single quotes into the form at all (as it is now), however this may aggravate anyone named say... Bill O'Reilly for the name field, etc., etc.
There are probably other (well I don't know what to call them, 'plug-ins?' 'outside programs?') that would do the job for me, but that is virtually useless since not only do I have no idea how to integrate that, I would have no idea how to tailor it specifically to my web interface/database.
Is there any code that could help me detect a sql injection apostrophe (by the characters surrounding it maybe?) from a normal apostrophe? Keep in mind some of my fields can hold up to 500 characters (textareas) and one up to 1,000.
Thanks for any ideas or help!
No amount of input encoding/cleanup will be as safe as parametrized queries.
See SqlCommand.Parameters for details on parametrized queries.
string commandText = "SELECT * FROM Sales 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;
var reader = command.ExecuteReader();
//.....
}
SQL Injections is not a problem with the input containing specific characters, it's a problem with how you handle the input.
By disallowing certain characters you can stop the obvious ways to cause SQL injections, but it's virtually impossible to use that to stop all possible ways.
If encoded correctly, there are no character that causes problems. The best way of doing that for database calls is to use parameterised queries, so that the database driver takes care of encoding the correct characters according to the data type and the specific database.
Also, you need to encode the values correctly when you use them later on, like HTML encoding strings that are put in HTML code, URL encoding strings that are used in an URL (and both for strings that are put in an URL in the HTML code.)
You should use parameterised queries to prevent SQL Injection as other people have already said.
Alexei Levenkov provides a good example of using ADO.NET parameters, but more commonly, you will use the Database Helper when working with WebMatrix Razor pages (ASP.NET Web Pages Framework) where parameter handling is slightly different. The Database.Query method (Query(string commandText, params object[] parameters) takes a string representing the SQL to be executed, and an array of objects, representing the parameter values to be passed to the SQL. The Database helper expects parameter markers to start at #0, and increment by 1 each time e.g.
var sql = "SELECT * From MyTable WHERE TheDate > #0 AND ID > #1";
Then you pass actual values in the following manner:
var data = Database.Open("MyDb").Query(sql, Request["date"], Request["id"]);
Internally, the Database class takes care of matching values to placeholders and creating ADO.NET parameters for you.
I been reading a bit about SQL injection and I want to be sure my code is lets say "safe" from it, I was planning on using RegExp validators to check the user input but another post in here suggested only using parametrized querys, well I'm using them but I want to be sure my code is safe, is it?
using ( SqlConnection dataConnection = new SqlConnection(myConnectionString) )
{
using ( SqlCommand dataCommand = dataConnection.CreateCommand() )
{
dataCommand.CommandText = "INSERT INTO Lines (Name, CreationTime) " +
"VALUES (#LineName, #CurrentDateTime)";
dataCommand.Parameters.AddWithValue("#LineName", TextBox2.Text);
dataCommand.Parameters.AddWithValue("#CurrentDateTime", DateTime.Now.ToString());
dataConnection.Open();
//do other DB stuff
I chop the last part to make the post shorter, the rest is just trying and catching exceptions and closing db connection as well as providing user feedback on inserting successful.
Your code is fine, it is protected from injection because the values are passed as parameters not string literals. However, if you are writing this type of data access yourself, have you considered creating SqlParameter objects and explicitly setting the type, size etc, and adding the parameters to the command? AddWithValue will work just fine, but SQL Server will have to determine the type, a little, but unnecessary overhead.
Well, you could always try to inject a SQL statement into the textbox, that will probably give you a quicker, definite answer.
Yes, that's reasonably safe. So long as you don't use "sanitized" variables from a prepared statement to generate dynamic sql later, you're usually ok. The fact that you're using a prepared statement will take care of dealing with escape characters and other simple methods of injection.
I wouldn't forgo any other validation though...
So throughout my program I have probably 50 or so text boxes in various places. I know how to replace a single quote with something (in this case ' -> \'), but I am thinking there must be a better way to do this than go through and add specific code for every single text box. I have to do this because when this stuff is getting sent to the database, if there is a single quote, it gives an error. Is there a way to change the default TextBox control behavior so that all textboxes in the program automatically replace all single quotes with \'?
EDIT:
string statement = "select count(*) from users where username='#username'";
MySqlCommand command = new MySqlCommand(statement, conn);
command.Parameters.AddWithValue("#username", username);
if (Convert.ToInt32(command.ExecuteScalar()) == 1)
I have been playing with the paramerterized code and this is what I have right now. From how I understand it, the statement string is basically the same as before, but where I used to have the variable "username" I know use a parameter (which I called #username), then the command is created. Then in the parameters.addwithvalue, it replaces the parameter username, with whatever is in the variable username. Unfortunately, this is not working for me, and I don't really see how it helps because username is still just getting stuck in the command?
EDIT: Found the problem, in the statement you don't need to put single quotes around '#username'
so it should be:
string statement = "select count(*) from users where username=#username";
Don't use concatenation to build SQL queries. Use proper parametrized queries. This will make repeated queries a bit faster and will also eliminate input sanitizing code (replacing ' with \' for example) and SQL injection attacks.
You should be using parameterized queries, not only to resolve the problem you have, but also to reduce your exposure to SQL injection. When you use string concatenation to build SQL queries you are suseptable to SQL injection attackes.
U can use onKeyUp javascript function or asp.net OnTextChanged event to create function that will change quotes.
I'm working with a datagrid and adapter that correspond with an MSAccess table through a stored query (named "UpdatePaid", 3 paramaters as shown below) like so:
OleDbCommand odc = new OleDbCommand("UpdatePaid", connection);
OleDbParameter param;
odc.CommandType = CommandType.StoredProcedure;
param = odc.Parameters.Add("v_iid", OleDbType.Double);
param.SourceColumn = "I";
param.SourceVersion = DataRowVersion.Original;
param = odc.Parameters.Add("v_pd", OleDbType.Boolean);
param.SourceColumn = "Paid";
param.SourceVersion = DataRowVersion.Current;
param = odc.Parameters.Add("v_Projected", OleDbType.Currency);
param.SourceColumn = "ProjectedCost";
param.SourceVersion = DataRowVersion.Current;
odc.Prepare();
myAdapter.UpdateCommand = odc;
...
myAdapter.Update();
It works fine...but the really weird thing is that it didn't until I put in the odc.Prepare() call.My question is thus: Do I need to do that all the time when working with OleDb stored procs/queries? Why? I also have another project coming up where I'll have to do the same thing with a SqlDbCommand... do I have to do it with those, too?
This is called, oddly enough, a prepared statement, and they're actually really nice. Basically what happens is you either create or get a sql statement (insert, delete, update) and instead of passing actual values, you pass "?" as a place holder. This is all well and good, except what we want is our values to get passed in instead of the "?".
So we prepare the statement so instead of "?", we pass in parameters as you have above that are going to be the values that go in in place of the place holders.
Preparing parses the string to find where parameters can replace the question marks so all you have to do is enter the parameter data and execute the command.
Within oleDB, stored queries are prepared statements, so a prepare is required. I've not used stored queries with SqlDB, so I'd have to defer to the 2 answers previous.
I don't use it with SqlDbCommand. It seems as a bug to me that it's required. It should only be nice to have if you're going to call a procedure multiple times in a row. Maybe I'm wrong and there's a note in documentation about providers that love this call too much.
Are you using the JET OLEDB Provider? or MSDASQL + JET ODBC?
You should not need to call Prepare(), but I believe that's driver/provider dependent.
You definitely don't need to use Prepare() for System.Data.SqlClient.