I'm working a C# form application that ties into an access database. Part of this database is outside of my control, specifically a part that contains strings with ", ), and other such characters. Needless to say, this is mucking up some queries as I need to use that column to select other pieces of data. This is just a desktop form application and the issue lies in an exporter function, so there's no concern over SQL injection or other such things. How do I tell this thing to ignore quotes and such in a query when I'm using a variable that may contain them and match that to what is stored in the Access database?
Well, an example would be that I've extracted several columns from a single row. One of them might be something like:
large (3-1/16" dia)
You get the idea. The quotes are breaking the query. I'm currently using OleDb to dig into the database and didn't have an issue until now. I'd rather not gut what I've currently done if it can be helped, at least not until I'm ready for a proper refactor.
This is actually not as big problem as you may see it: just do NOT handle SQL queries by building them as plain strings. Use SqlCommand class and use query parameters. This way, the SQL engine will escape everything properly for you, because it will know what is the code to be read directly, and what is the parameter's value to be escaped.
You are trying to protect against a SQL Inject attack; see https://www.owasp.org/index.php/SQL_Injection.
The easiest way to prevent these attacks is to use query parameters; http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlparameter.aspx
var cmd = new SqlCommand("select * from someTable where id = #id");
cmd.Parameters.Add("#id", SqlDbType.Int).Value = theID;
At least for single quotes, adding another quote seems to work: '' becomes '.
Even though injection shouldn't be an issue, I would still look into using parameters. They are the simpler option at the end of the day as they avoid a number of unforeseen problems, injection being only one of them.
So as I read your question, you are building up a query as a string in C#, concatenating already queried column values, and the resulting string is either ceasing to be a string in C#, or it won't match stuff in the access db.
If the problem is in C#, I guess you'll need some sort of escaping function like
stringvar += escaped(columnvalue)
...
private static void escaped(string cv) as string {
//code to put \ in front of problem characters in cv
}
If the problem is in access, then
' escapes '
" escapes "
& you can put a column value containing " inside of '...' and it should work.
However my real thought is that, the SQL you're trying to run might be better restructured to use subqueries to get the matched value(s) and then you're simply comparing column name with column name.
If you post some more information re exactly what the query you're producing is, and some hint of the table structures, I'll try and help further - or someone else is bound to be able to give you something constructive (though you may need to adjust it per Jet SQL syntax)
Related
I am attempting to use ExecuteSqlInterpolated to update my database. However, it seems that there is a problem with my SQL parameters. Running the following code correctly updates intField1 and intField2, however stringField becomes the string "#p0".
_context.Database.ExecuteSqlInterpolated($"UPDATE table SET stringField='{someString}', intField1={someInt}, intField2={someOtherInt} WHERE id='{id}'");
I have already verified that my variables contain the desired values when the string is passed to the method. I understand that #p0 is what SQL uses to represent the first parameter in the query, but why isn't it being replaced by the string I gave it? I have also tried using ExecuteSqlRaw but ran into the same issue. My knowledge of SQL is limited at best, I know just enough to get by in web dev, so I'm guessing I'm committing some simple error in crafting the query here, but obviously I'm not sure.
I know it's late but just don't use quotation mark with your parameters, specially where you use int data-type
(delete single quotes)
_context.Database.ExecuteSqlInterpolated($"UPDATE table SET stringField={someString}, intField1={someInt}, intField2={someOtherInt} WHERE id={id}");
I have the following C# function
SomeFunction(string table, string column, string where) {
Sql sql = new Sql("SELECT ");
// [...] validate table and column values
sql.Append(column);
sql.Append(" FROM ");
sql.Append(table);
sql.Append(" WHERE ");
sql.Append(where); // This is the issue
}
As you can see this is awful, I'm dealing with this very old legacy code and changing the function signature and the way the clients use it is just not feasible. What I have to do is secure the 'where' clause. This clause may contain any number of conditions and data types.
I had a bunch of ideas but I don't think they are a good solution, I think this requires a properly written and tested code, but if I do it myself out of the blue it'll probably have holes. Here are some thoughts:
Splitting the string by char '=' -> what if that's not the condition operator
Find if string contains semicolons -> the SELECT clause remains vulnerable, and maybe one of the conditions contains that char so it'd give a false positive
If you have any idea/suggestion/pointing in the right direction I will be most grateful.
If the where clause is currently based on being a pre-composed string, then frankly I don't think it is a viable approach to attempt to "secure" it. It is theoretically possible, but any attempt at parsing the SQL will fail if the composed and compromised (injected) where clause is legitimate (but abusive). At that point: you've already lost track of the original intent. That's kinda the entire point of SQL injection: the resultant SQL is valid SQL - so it is very hard for you to tell the difference between where Name = 'Fred Orson' -- check name (probably fine) and where Name = 'Fred' Or 1=1 --' (injected - query widening).
So: while I acknowledge that you say:
changing the function signature and the way the clients use it is just not feasible.
Not changing the function signature doesn't really help you solve the problem. Trying to detect certain patterns is just an arms race, where you need to win every time and the attacker needs to win only once.
If it was me, I'd be doing something like:
[Obsolete("Please specify parameters separately - use 'null' if no parameters are needed")]
SomeFunction(string table, string column, string where) {
return SomeFunction(table, column, where, null);
}
SomeFunction(string table, string column, string where, object args) {
// ...
}
and using an approach like "Dapper" uses to compose the parameters from the args parameter - or just use "Dapper" itself to run the query, and use that functionality for free.
This approach:
prevents new uses of the dangerous API being added
lets the existing code continue to work for now
but lets you track how many outstanding problem calls there are, by watching the warnings
Edit: note: the point of the args parameter is to allow the caller to parameterize their inputs, i.e.
string name = ...
var users = SomeFunction("Users", "Id", "Name=#name", new { name });
With SomeFunction decomposing args and adding parameter name/value pairs from the properties on args (if it is non-null). There are various approaches to composing parameter sets, but the approach shown here is simple and easy to implement correctly - which makes it a clear win for me.
I'm working with an asp.net website that uses a lot of inline SQL queries... and I'm wondering if it is best to create the inline queries on the fly:
int i = 500;
using (SqlConnection conn = new SqlConnection(connStr))
{
SqlCommand com = new SqlCommand(conn);
...
com.CommandText = "select from table where column < #parameter";
...
}
Or to have a class to hold all queries needed for the application. Something like this:
class SqlQueries
{
private string query1 =
"select * from tblEmployees where EmployeeName = #EmployeeName";
private string query2 =
"select * from tblVacation where EmployeeName = #EmployeeName";
public string Query(string s)
{
string str = string.Empty;
switch (s)
{
case "query1":
str = query1;
break;
case "query2":
str = query2;
break;
}
return str;
}
}
Thank you!
I've used a lot of ADO.NET queries in my day and I have always used the first method. The second method is an interesting idea, but it might be cumbersome to edit those queries if you are at another place in the code that uses it. It also makes it harder to see what a query is doing at a particular place in code. Example:
string sql = "Update User set age = #age where UserId = #UserId";
tells a developer what is happening, while:
string sql = SqlQueries.Query("updateAge");
Leaves questions about what table/columns are being updated. Also, with the first one, you know exactly what params need to be added.
If you are writing this query in several places that might change things
It's not terrible to put the literal directly in the method, as long as you always call that same method every time you want to run that query. However, if you are going to copy that string literal into multiple places in your code, then a constant is definitely preferred. However, rather than taking a string as the argument for the Query method in your second example, it should take an enumeration value.
However, if you are using the second method you described, I would ask you why you don't just start using stored procedures instead?
I would recommend using stored procedures as a much better solution to your problem than hard coded in-line queries. If you have to change the query at a later date, you don't have to rebuild your application, so bugs in your query can be fixed without needing to deploy the whole application. The 2nd option you have there is a maintenance nightmare waiting to happen. It all looks so nice when you have one or two queries in it, but that begins to look a bit more ugly when you have tens or hundreds in there. Your code looks like it's c#, so I would recommend checking out the Microsoft Enterprise Library,
http://msdn.microsoft.com/en-us/library/ff632023.aspx
You might need to download a different version depending on what version of the .NET framework you are developing with.
If you absolutely have to have "inline" sql as opposed to stored procedures (and I have done this for utility type applications that merely interact with a database, rather than own it), I would suggest putting your SQL into an embedded resource file. This will make your queries easier to maintain (although you will still need to re-compile your app to make changes).
I think it's OK to have the queries "inline" as long as they aren't repeated in several places. If that starts to happen, then you might want to start creating Query classes.
In both the cases you are ultimately building/fetching String which you will pass to CommandText. So there would be no such difference. Only thing you need to consider in your case is how you would maintain the code or how will other people understand your code.
If you're going to use inline SQL at least don't put it in the web page code because it will be painful when you make database changes to know what it affects. Putting all the queries in one classes might be a bit disorganized, but if you grouped them by functional classes (like manager classes for your business objects) it might be easier to deal with.
If your queries are longer than a line or two, you should consider putting them in their own .sql file. Set the build action on the file to embedded resource, and access it with a call to GetManifestResourceStream(). That way, you're elevating your sql to the status of a proper language, with syntax highlighting, validation and intellisense (when you connect VS to your DB). Needless to say, this hugely facilitates maintenance.
If all this seems like a hassle, grab my VS extension, QueryFirst. Create your .sql files with the provided template and they will automatically be wired up for compilation. But you won't care because you'll just access the queries via the generated classes.
Sql is the only computer language I can think of that we accept to see chopped up in string literals. It ought to be a scandal.
Suppose I'm querying a Sql Server DB for row count based on a LIKE comparison on a column whose value is supplied via windows form text input. Using parameters here is important due to possible user input leading to injection. Eventually I'm to execute member function ExecuteScalar() on an instantiated SqlCommand object I named cmd, but first I've to add the parameter. For example:
cmd.Parameters.AddWithValue("#param1", textBox1.Text);
Sql Server uses the special character % as a wildcard match for the LIKE comparison. What I wanted to do was allow the user to use * for wildcards instead. Hence, a simple replace:
textBox1.Text.Replace('*','%');
The problem is I run into issues with values containing special symbols % and _. One way to search for a literal % rather than use it as a wildcard is to enclose it in square brackets: [%].
So, now my replace has to become:
textBox1.Text.Replace("%","[%]").Replace("_","[_]").Replace('*','%');
Order is important here as well, since if the last Replace were made sooner the % would be treated incorrectly.
I'm not sure I've covered all my bases, are there other characters I need to worry about here? Does this really protect from injection? Is there some other preferred way of doing this?
An example query might be something like this:
SELECT COUNT(*) FROM [MyTable] WHERE [Column1] = #param1
Where MyTable is your table name, and Column1 is a valid column name within MyTable. We can assume that Column1 is some nvarchar type.
You shouldn't really need anything else, but I'd make sure to test oddball things from user input. Some characters you haven't accounted for have special meaning in LIKE:
^
-
Since you're passing a parameter into the statement and not blindly appending the string, there should be little danger of injection, but you may want to try variations of user input such as:
foo'; DELETE dbo.[UnimportantTable];
foo''; DELETE dbo.[UnimportantTable];
foo''''; DELETE dbo.[UnimportantTable];
Again, I'm not sure if you're vulnerable because I can't see the whole thing, but I do think it's very easy to construct a variety of tests so that you know all of the potential outcomes with a wide sampling of potential inputs.
As #Bryan pointed out, certainly a good way to limit the risk is to connect using a login that has very explicit read-only permissions only on the objects you want them to be able to read. Then even if they do exploit some hole in your scaffolding, getting in doesn't buy them much.
I have a SqlDataAdapter that looks something like:
("Select prodID, CatalogType, prodName, catID, Integration, ItemProfileCatalogID From ShoppingCart t1
INNER JOIN ItemCatalogProfile t2 ON t1.CatalogType = t2.CatalogType
WHERE SessionID = '" + Session["ID"] + "' AND CatalogID ='" + Session["Customer"] ....)
there are a few more included in the where statement, but the one I cannot seem to get to work is:
ItemProfileCatalogID ..
I need to include this to narrow down the items down to only one of each and this variable will do just that if I can figure out what to use in this statement.
I've tried
viewstate[""]
Request.QuerryString[""]
Session[""]
and I cant seem to get those to work..
The problem I am having is, the current shopping cart if I do not have this item to filter, it will return every instance of that particular product in the database because there are up to 250 listings of one item for different catalogs, and that is where the ItemProfileCatalogID comes in, that will filter it down to just the one item
Any suggestions?
Thank you
CatalogID is probably numeric and you are using it as a string in your SQL statement.
It could also be that you have some syntax error in your SQL statement not easily detectable with all the string concatenation going on or due to CatalogID containing a naughty character (' for example)
Also, please check out parametrized queries; concatenation when building SQL statements is usually not a very good idea (SQL injection).
As InBetween said it probably is an issue with it being numeric, you should be able to use the .toString() method to solve this.
Also Stored procedures are generaly more advisable to use for a number of reasons, in your case you mentioned you are working with a shopping cart which suggests maybe some kind of ecommerce application? Using a stored procedure here will mean that SQL does not have to compile your select statement every time you run it thus improving performance and having the code in a stored proc will also increase maintainability and possibly allow you to reuse the procedure in other places.
Added to this you are not actually transmitting the select statement over the network which increases security as no one can intercept this and gain insight into your table structures, and as InBetween mentioned above a stored procedure will help you protect against injection attacks or just simply unforseen data as you can add error handling more easily.