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("'", "''"));
Related
I am new to SQL Server, I am trying to insert records into table using a stored procedure as shown below.
I want a suggestion that is using the below stored procedure. Also:
can I prevent SQL injection?
is it the right way?
Correct me if I miss anything in below procedure which leads to SQL injection.
Create PROCEDURE [dbo].[spInsertParamTable]
#CmpyCode nvarchar(50),
#Code nvarchar(50),
#DisplayCode nvarchar(50),
#TotalDigit int,
#Nos bigint,
#IdentitY int OUTPUT
AS
BEGIN
INSERT tblParamTable (CmpyCode, Code, DisplayCode, TotalDigit, Nos)
VALUES (#CmpyCode, #Code, #DisplayCode, #TotalDigit, #Nos)
END
SELECT #Identity = SCOPE_IDENTITY();
RETURN #Identity
SQL Injection specifically refers to injecting SQL code into an existing SQL query that's built up via string concatenation and executed dynamically. It is almost always of the form:
#dynamicSQL = "select * from sensitivetable where field = " + #injectableParameter
sp_executesql #dynamicSQL
For this particular stored procedure, the worst an attacker could do is insert unhelpful values into your tblParamTable.
However, if these values are then used in a dynamically-built query later on, then this merely becomes a second-order attack: insert values on page 1, see results of dynamic query on page 2. (I only mention this since your table is named tblParamTable, suggesting it might contain parameters for later re-use.)
Can I prevent SQL injection?
You already are - there is no way to "inject" code into your SQL statement since you're using parameters.
Is it the right way?
Well, there's not one "right" way - but I don't see anything seriously wrong with what you're doing. A few suggestions:
You don't need to RETURN your output parameter value. Setting it is enough.
You have the last SELECT outside of the BEGIN/END block, which isn't hurting anything but for consistency you should put everything inside BEGIN/END (or leave them out altogether).
I've got a good grasp on SQL injection. It's when a SQL query that is supposed to be something like
SELECT FirstName, LastName
FROM Customers
WHERE CustomerId = #valueFromApplication
Gets turned into a query like
SELECT FirstName, LastName
FROM Customers
WHERE CustomerId = '' ; DROP DATABASE Foo --
When the user inserts a malicious value into your app, website, client, whatever.. I'm also aware that instead of just dropping the DB the attacker can try to discover the names of tables and get info out of them.
I also know some things that help prevent this are:
Using stored procedures which take parameters (SQL Server)
Using parametrized SQL queries
Using Entity Framework / LINQ to Entities (C#, maybe F#?)
How do these things actually prevent SQL injection from occurring? Why can't the attacker just pass the same malicious value into whatever input he or she is already using and have the same result.
Your first example is parameterised and is not vulnerable to SQL injection.
Parameterised queries aren't simply replaced by the server with values (like you might do manually replacing #var with value). They are sent and received exactly as you sent it.. with #valueFromApplication.
The server will parse the query.. and when it gets to a variable it will look up the value supplied. If that value is '' ; DROP DATABASE Foo --.. then that becomes the value it uses. It doesn't parse that.. it just uses it as text/number/whatever type it is.
To add about Entity Framework, it internally uses Parameterised query so it is also SQL injection safe.
Parameters are not simply replaced in-line into the SQL - they are sent separately from the query to the SQL Server.
So, SQL Server gets something like:
Query:
SELECT FirstName, LastName FROM Customers WHERE CustomerId = ?
Parameter 1:
'' ; DROP DATABASE Foo --
And therefore it compiles a query that checks for a customer whose CustomerId is literally equal to '' ; DROP DATABASE Foo --. The parameter value is never executed as SQL.
As an extension to How to protect user specified table name from SQL Injection in C#, using MySQL, I'm trying to figure out how to protect the user-specified-table-query from SQL Injection:
string createEventSQL = "INSERT INTO " + TableNameFromUser +
" (" + TableColumnNames + ") " +
"VALUES(" + ParametrizedTableColumnParams + ")";
To be clear: I would love to use a predefined library to parametrize the input, but I can't find one.
I don't want additional queries (e.g. SHOW TABLES LIKE #TableNameFromUser;) to secure this, since performance is an issue.
It seems to me that many people claim that it isn't possible to to make a 100% secure solution, but that doesn't make sense to me, since resorting to parametrization should be just as "insecure" as doing all the work yourself. Essentially, I just want to replicate what the MySQL Connector would do, if it supported parametrized table names.
I'm not very experienced with SQL yet, but so far I've found that I need to:
Escape/disable all escapable characters.
Disable "--"
What else is can be done to protect from SQL Injection?
The MySQL Ado connector supports parameters on MySqlCommand - here.
As you've identified, in general, you should always pass parameters instead of mangling ad hoc SQL.
Unfortunately, this won't parameterize the table name, as per this SO post : MySqlParameter as TableName.
So it looks like you will need to validate and sanitize the table name.
Can you compare the table name against a white list? Or possibly keep a list of valid tables names somewhere else in the database?
You can, and should, parameterize your data values. You know that.
You can't parameterize your table names and column names using SQL's prepared statement feature. However, you should establish and enforce constraints on what can be in your user-furnished table and column names. For example, you could insist that table and column names all start with a letter, and consist of between 3 and 15 characters from the set of letters, numbers, and underscores. You can easily write a checker function that will throw an exception for user-furnished names that break the constraint, and always check the names with that function when composing a query.
For the sake of performance, you've ruled out checking the table and column names against the schema in your dbms. You might want to reconsider that decision: these queries aren't as slow as you think they are. The MySQL information schema lets you do queries like this:
SELECT COLUMN_NAME
FROM information_schema.COLUMNS
WHERE TABLE_SCHEMA = 'zip'
AND TABLE_NAME= 'zip'
This will give you a nice list of columns in the table you've specified.
My question is generally we write the following through code while we are inserting data to a table
insert into tblname values('"+txt.text+"','"+txt1.text+"');
As we pass the data form the text boxes like that is it possible to insert in to table with out using table name directlty
Well you obviously need to know what table to insert into, so there has to be a table name identified to the INSERT statement. The options include:
an INSERT statement with actual table name as per your existing example
an INSERT statement with a synonym as the target (alias for an actual table - see: http://blog.sqlauthority.com/2008/01/07/sql-server-2005-introduction-and-explanation-to-synonym-helpful-t-sql-feature-for-developer/)
an INSERT statement with an updateable view as the target
a sproc call whereby the sproc knows the table to INSERT into (but the calling code does not need to know)
You should also be aware of SQL injection risks with your example - avoid concatenating values directly into a SQL string to execute. Instead, parameterise the SQL.
If you need to dynamically specify the table to insert into at run time, you have to concatenate the table name into the SQL statement you then execute. However, be very wary of SQL injection - make sure you fully validate the tablename to make sure there are no nasties in it. You could even check it is a real table by checking for it in sys.tables.
Not possible without name of table.
But you can make use of Linq To SQL (i.e any ORM) or DataAdapter.Update if you have filled it with the proper table....
You cannot do that without the table name, no. However, the bigger problem is that your code is horribly dangerous and at rick from SQL injection. You should fix this right now, today, immediately. Injection, even for internal apps, is the single biggest risk. Better code would be:
insert into tblname (Foo, Bar) values(#foo, #bar)
adding the parameters #foo and #bar to your command (obviously, replace with sensible names).
Before you ask: no, the table name cannot be parameterised; you cannot use
insert into #tblname -- blah
The table name(s) is(/are) fundamental in any query or operation.
I suppose that if it's possible you have to use parameters.
Here you have a little example.
I am developping an ASP2.0 website with a Microsoft SQL server 2005 Database.
I need to implement a functionality which allows users to create a select query (nothing too complex) so that the website displays a page with the result set of the query.
My question is how can I sanitize the query to make sure there is no insert/update/delete/drop or other nefarious injection.
also, I need to encapsulate the query in a "with" clause so that I can add an identity column to the result set. (I need that to display the results correctly on the page)
my CSharp code to format the query looks like this (simplified a little):
string query = txtQuery.Text;
query = query.ToLower();
query = query.Trim();
int orderByIndex = query.LastIndexOf("order by");
string orderBy = "";
if (orderByIndex != -1)
{
orderBy = query.Substring(orderByIndex);
query = query.Replace(orderBy, "");
}
query = "with query as (" + query + ") select row_number() over(order by (select 0)) as rowID, * from query " + orderBy;
I want to create a stored procedure to execute the query. I was thinking of something like this:
CREATE PROCEDURE usp_execute_query
#sql nvarchar(max)
with execute as 'RestrictedUser'
as
begin
exec sp_executesql #sql
end
with RestrictedUser looking like this:
CREATE USER RestrictedUser WITHOUT LOGIN
EXEC sp_addrolemember db_datareader, RestrictedUser
My questions are:
Is there a way to check the roles of RestrictedUser within the stored procedure to make sure they haven't been tampered? And raiserror if they have.
Do you think this whole thing is the right way to go? Any suggestion?
Danger Will Robinson! Any time you're allowing a user to pass arbitrary SQL, you're running into all sorts of security issues. The odds of you plugging every hole are slim. Plus, the ability to "sanitize" a query is predicated on your ability to parse the query. It is possible to parse SQL yourself, but it's not trivial by any stretch of the imagination. Also, because this is a web app, you're pitting your skills against a lot of people with probably more experience performing sql injection attacks.
Creating the user with very limited permissions is a good thing (and likely your best shot). However, you will need to be fastidious about what they have access to (system stored procs, system views, etc). In other words, db_datareader is not limited enough. You'll want to create an entirely new rule and only given them permission to very specific items.
Keep in mind that even though you might succeed in limiting what pieces of data the user (aka hacker in this scenario) can see, you're still vulnerable to DOS (Denial of Service) attacks.