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
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.
Hello I'm security testing a website I'm working on. Some developer tried to avoid SQL injection by replacing every single quote with double quotes. This is the C# code:
string sql =
#"SELECT *
FROM users
WHERE us_username = '$us'
AND us_password = '$pw'";
sql.Replace("$pw", txtPassword.Text.Replace("'","''"));
Is there any way that I can perform a SQL injection attack? I've tried the Unicode trick but it didn't work. The database runs on SQL Server 2008R2.
You should use parameterized command instead. Using string.Replace is just a bad idea.
var command = conn.CreateCommand();
command.CommandText = #"SELECT *
FROM users
WHERE us_username = #user
AND us_password = #password";
cmd.Parameters.Add("#user", txtUser.Text);
cmd.Parameters.Add("#password", txtPassword.Text);
This might be a potential candidate for your setup :
As an example, note the following trivial Stored Procedure:
create procedure GetData ( #param varchar(20) ) as
begin
declare #s varchar(200)
select #s = 'select * from dataTable where name = ''' + #param + ''''
exec (#s)
end
This SP may be called from a Web page, which executes validation code
before passing the input to the SP. At a minimum, this validation code
either verifies that the input does not contain a quote, or sanitizes
it to double any existing quote. For instance, the validation code may
be using string.Contains(), string.Replace(), Regular expressions,
etc. It is also possible that this Web page is behind a finely-tuned
Web Application Firewall that validates all input and verifies that no
quotes are included. A malicious user or attacker can submit malicious
code containing a modifier letter apostrophe (U+02BC, URL encoded to
%CA%BC). This will easily pass applicative validation code and WAF
filters, since these search for an actual quote (U+0027) which does
not exist in the input at this time. Obviously, IDS/IPS systems would
also not detect anything amiss. The validation mechanisms may even
search for various encodings of a quote, such as URL Encoding, UTF-8
encoding, Hex encoding, double encoding, and more – however, U+02BC is
none of these, and is in fact a completely different character value.
And this is where the interesting (or scary) part starts – the Unicode
homoglyph translation is not limited to base alphabet characters...
Specifically, the Unicode character U+02BC (modifier letter
apostrophe) can be translated by the database server to a simple quote
– ' (U+0027). There are, of course, many other similar examples.
Source : http://web.archive.org/web/20130401091931/http://www.comsecglobal.com/FrameWork/Upload/SQL_Smuggling.pdf
The code for that partical query is safe from SQL injection, but only when used with a certain databases. Each system has its own set of characters that needs escaping, so if you use that with for example MySQL then it's not safe. Other queries might not be safe.
The code should be replaced nevertheless as it is broken. As you need to fix the code you should also change it to using parameterised queries, which is a more robust and portable solution.
So, let's see what's broken. As the code is replacing one parameter at a time, they may interfer with each other. If I for example enter the user name has$$$pwnd and the password 1234 (yeah, weak password), you end up with a query that looks like:
SELECT *
FROM users
WHERE us_username = 'has$$1234nd'
AND us_password = '1234'
If some values contain the codes that is used for parameters replaced after it, the values become broken.
This could even be used to make an SQL injection in other queries in the code, if there are parameters of different types and the values are not properly verified. As values from one parameter can end up in another parameter, a string value could end up in a numeric parameter which doesn't have apostrophes around it, thus there is no need to sneak in an apostrophe to break out of a string literal to put harmful code in the query.
The best way to counter SQL Injection is to add parameters.
SqlCommand sql = new SqlCommand (#"SELECT *
FROM users
WHERE us_username = #user
AND us_password = #password")
sql.Parameters.Add("#users", SqlDbType.Varchar2, 5).Value = "users";
sql.Parameters.Add("#user", SqlDbType.Varchar2, 6).Value = "your_value";
sql.Parameters.Add("#password", SqlDbType.Varchar2, 8).Value = "your_value";
As you can see, you can do quite a bit to ensure what is being executed are the values that you want to only get executed.
What the developer has coded will only alter the sql statement after the fact, which is good if they are logging this sql statement. What you have now however will not protect against Sql Injection.
I am working with C#. I need to write a select inline query.
The table name should be taken from config. I cannot write a stored procedure.
SqlCommand myCommand= new SqlCommand();
myCommand.CommandText = "Select * from " + tableName;
myCommand.CommandType = CommandType.Text;
myCommand.Connection = connString;
How to avoid sql injection ?
Just create a query with a real param and check for the existence of the tablename - somthing like:
SELECT COUNT(*) FROM SYS.TABLES WHERE NAME = #pYOURTABLENAME
IF that returns 1 then you know that the table exists and thus can use it in the SELECT you showed in the question...
However I strongly recommend to try anything to get rid of the need for any code prone to SQL injection!
I would ensure table name contains only these characters:
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz[]. -_0123456789
E.g.,
Regex regex = new Regex(#"^[ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz\[\]. -_0123456789]{1,128}$");
if (!regex.IsMatch(tableName)) throw new ApplicationException("Invalid table name");
To do a more comprehensive job including non-English languages see this reference on what a valid table names:
http://msdn.microsoft.com/en-us/library/ms175874.aspx
You need to verify that tableName is appropriate. After some sanity checking (making sure it has no spaces, or other disallowed characters for table names, etc), I would then first query the database for the names of all tables, and programmatically verify that it is one of those table names. Then proceed to run the query you show.
I'd look at moving the SQL to a stored proc and review this article by Erland Sommarskog as it has some great ideas for using dynamic SQL within stored procs. I'd certainly look into it. It discusses a lot of the issues around SQL injection and possible alternatives to dynamic SQL.
He also has another great article on ways to use arrays in stored procs. I know you didn't ask for that, but I often refer to these two articles as I think they are quite insightful and provide you with some useful ideas with regards to writing your procedures.
In addition to some of the suggestions linked above, I still have some basic parameter sanitisation mechanisms that I use if I am ever using dynamic SQL. An example of this is as follows;
IF LEN(#TableName) < 5 OR LEN(#TableDisplayName) < 5
BEGIN
RAISERROR('Please ensure table name and display name are at least 5 characters long', 16, 1)
END
IF NOT (#TableName not like '%[^A-Z]%')
BEGIN
RAISERROR('The TableName can only contain letters', 16, 1)
END
IF NOT (#TableDisplayName not like '%[^0-9A-Z ]%')
BEGIN
RAISERROR('The TableDisplayName can only contain letters, numbers or spaces', 16, 1)
END
This combined with using parameters within your dynamic sql and then executing using sp_executesql certainly help to minimise the possibility of a SQL injection attack.
I am using C# to parse a chat log and insert messages into a database.
When trying to insert the string "Don't worry, it's unloaded"
(with the double quotes) it gives me the following exception:
System.Data.Odbc.OdbcException: ERROR [HY000] [MySQL][ODBC 5.1 Driver][mysqld-5.5.11]Incorrect string value: '\xEF\xBB\xBF it...' for column 'msg' at row 1
at void System.Data.Odbc.OdbcConnection.HandleError(OdbcHandle hrHandle, RetCode retcode)
The database is using latin-1 default collation for the encoding scheme.
I have tried switching to utf-8 but this gave me the error on the same line.
Not sure what it means to your specific error, but EF BB BF is the UTF BOM character which could be causing an issue.
This answer pointed out that the client connection needs to be set to the proper character set as well. It could be that the C# client character isn't matching the MySQL encoding.
Depending on your chosen way to insert data (I assume by building the SQL directly), the ' character needs to be escaped. That's because ' is string delimiting character in most databases.
What you need to insert is "Don''t worry, it''s unloaded", with the single quotes escaped by doubling them.
!Important: You need to be careful about raw using raw SQL as it can easily create security holes that can SQL injection. Use parametrized queries whenever possible or fully escape the query sent to the server.
Don't forget that if you're constructing the SQL statement (don't! -- use a parameterized query instead), if the construct winds up looking like:
insert foo ( bar ) values( "This is my data" )
The insert will fail because the double quote introduces a quoted column name. It is not the same as a string literal which is quoted with the apostrophe (').
User SQL Parameters instead of using raw sql. There can be SQL Injection security issue and these sort of issues.
See how to use sql parameters mysql-c#
Eg:
MySqlCommand mySqlCommand1;
...
mySqlCommand1.CommandText = "INSERT INTO dept (deptno, dname, desc) VALUES (?, ?, ?)";
mySqlCommand1.Parameters.Add("param1", 30);
mySqlCommand1.Parameters.Add("param2", "SALES");
mySqlCommand1.Parameters.Add("param3", #"Don''t worry, it''s unloaded");
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)