While parameter is the best way to guard against Sql injection, there are times which we can't use it while building dynamic query. For example Table/Column/Index names cannot be passed in as parameter but only plain Text.
It seems like
SqlCommandBuilder.QuoteIdentifier
is the only option that I can find. Is calling this method enough to protect ourselves?
MSDN DOC:
Given an unquoted identifier in the correct catalog case, returns the
correct quoted form of that identifier. This includes correctly
escaping any embedded quotes in the identifier.
For example is
"Select * FROM " + SqlCommandBuilder.QuoteIdentifier("CustomTable" + userInputText);
safe to do?
Edit: The query is just an example. I am interested in finding out if Sql injection is ever possible.
It won't protect you from the attacker going to tables you don't want them to.
such as SQL system tables...
That may not be not safe to do.
To protect against any possible security problem with the SqlCommandBuilder.QuoteIdentifier method all that you need to do is get a list of the available table names etc. from the database and validate the user input against them.
Edited to add: I have reason to doubt if QuoteIdentifier is completely safe: the documentation for the SqlCommandBuilder.QuoteIdentifier Method says (as you previously quoted):
Given an unquoted identifier in the correct catalog case, returns the correct quoted form of that identifier. This includes correctly escaping any embedded quotes in the identifier.
Nowhere in that documentation does it state what happens if it is given an unquoted identifier in the wrong catalog case (whatever a "catalog case" is). Or what happens if the identifier is longer than the maximum allowed. Of course, undefined behaviour cannot be relied on.
Seems safe to do to me. Also, this might be a good reference:
Sanitize table/column name in Dynamic SQL in .NET? (Prevent SQL injection attacks)
Using user input in table name fields is never safe no matter how much you try to check it (unless you restrict the entries to a limited set of names or do some other kind of sorcery).
Even removing quotes, the user could type: TableName; DROP DATABASE db; or (SELECT * FROM <sensible table).
Possible solutions would be:
Using a ComboBox or an equivalent where the user can't modify the options
Check the input against a String[] with all allowed table names (where they should be identical to one of the entries)
and if the user input as a table name was just an example but you're going to use the input as part of a WHERE clause of a SELECT, then you should check Bobby Tables.
Quoted from the website:
From the C# Online wiki page ASP.NET Security Hacks--Avoiding SQL Injection
SqlCommand userInfoQuery = new SqlCommand(
"SELECT id, name, email FROM users WHERE id = #UserName",
someSqlConnection);
SqlParameter userNameParam = userInfoQuery.Parameters.Add("#UserName",
SqlDbType.VarChar, 25 /* max length of field */ );
// userName is some string valued user input variable
userNameParam.Value = userName;
Or simpler:
String username = "joe.bloggs";
SqlCommand sqlQuery = new SqlCommand("SELECT user_id, first_name,last_name FROM users WHERE username = ?username", sqlConnection);
sqlQuery.Parameters.AddWithValue("?username", username);
Have you considered using OData? you can pass in text, selecting tables, indexes and so on. But with OData you select what tables you want to publish this way, and it can't be injection attacked as you have to explicitly allow update and insert operations.
http://www.odata.org/documentation/odata-version-2-0/uri-conventions/
https://www.asp.net/web-api/overview/odata-support-in-aspnet-web-api
Related
Is there a way to write parameterized sql for different providers?
Example:
connection.QuerySingle<string>("select name from user where id = :id", new {id = 4});
This would work with an oracle provider but MsSql requires "#id" as parameter.
The Dapper FAQ says:
It's your job to write the SQL compatible with your database provider.
But how? Currently we have the following workaround:
$".. where id = {db.ParamToken}id"
But that's really ugly to write in larger SQL's.
Is there a way to have one token for all providers?
"Is there a way to have one token for all providers?"
Yes, but it requires some setup. You can retrieve useful database provider specific information from an existing DBConnection. First retrieve the DataSourceInformation table from the connection:
DbConnection connection = GetSomeConnection();
var infoTable = connection.GetSchema(DbMetaDataCollectionNames.DataSourceInformation);
That table will have a single row with various provider info. In regards to parameter naming, there will be a column named ParameterMarkerPattern which represents a Regex pattern string for validating the parameter. If that column has data, the first character will be your DbParameter marker. If the column is blank, the ParameterMarkerFormat can give you a string format to apply when building your parameter name.
"But that's really ugly to write in larger SQL's".
This doesn't really get around that if you're considering directly formatting your SQL, and your workaround is already much simpler than this. However the additional data you get from the DataSourceInformation should be enough for you to pass in your own string to a method of your creation, which would replace a default parameter start character (like #) with the proper one from the provider:
string sql = SqlIfy("SELECT name FROM user WHERE id = #id");
You can go even further with this and do the same for quoted identifiers. You can pass in something like:
"SELECT [Name] FROM [dbo].[SomeTable]"
and have it come out like
SELECT "Name" FROM "dbo"."SomeTable"
All depending on the provider. If you wanted to dynamically build queries on some custom base provider class, you could open an initial connection and store all of the provider specific data. You wouldn't want to call DbConnection.GetSchema each time you use a connection.
SQL Server:
Oracle:
I wanted to make my sql query bullet proof and found this question about sanitizing table/column names.
I followed the advices but somehow it doesn't work as expected.
My table name is foo.Bar so I passed it to the CommandBuilder's QuoteIdentifier method and it gave me [foo.Bar] back.
When I call (string)cmd.ExecuteScalar(); it complains that this table doesn't exist. So I tried to initially define the table name as [foo].[Bar]. In this case QuoteIdentifier creates [[foo]].[Bar]]] which also doesn't work.
The only thing that works is when I specify just [foo].[Bar] without using the QuoteIdentifier method.
At this point I'm wondering whether I can use it at all to protect my queries? It is not of much use and tuning the quoted query like another answer suggests also doesn't seem to be right.
Is there anything I can do to protect the query and make it work and accept the name [foo].[Bar] without breaking it?
This is how I'm creating the query:
cmd.CommandText = string.Format(
"SELECT {0} FROM {1} WHERE {2} = '{3}'{4}",
...,
sanitizedTableName, // only [foo].[Bar] works -- [[foo]].[Bar]]] and [foo.Bar] fail
...,
...,
...);
The problem is that the name of the table is bar, not foo.bar. You're using a multi-part identifier - foo is the schema, and bar is the table name.
To get proper quoting, you need to quote each identifier separately:
QuoteIdentifier(schemaName) + "." + QuoteIdentifier(tableName)
The reason for this should be obvious - it's perfectly valid for a quoted identifier to use . as part of the name. That's kind of the whole point of having quoting in the first place.
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.
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.