Re: SQL Injection Basics

["Jim McGarvey" <mcga0031 () umn edu>]

Mark:

I think you meant to first sanitize CInt(Request.QueryString("id")) to make
sure it's an integer.  If I'm not mistaken, you've given a perfect example
of code that is susceptible to SQL Injection mischief:

http://www.yourserver.com/yourscript.asp?id=1+OR+1=1
makes your query:
SELECT * FROM myTable WHERE id=1 OR 1=1

... which would return all the records from the table, instead of the one
intended, and that's just the beginning of what you could do.

You need to be sure to verify that the string you're appending to your sql
query is indeed just a number, and it's probably a good practice to do this
right before you execute the query.  Just because you hardcoded a numeric id
into a query string on your page (or validated a form with javascript)
doesn't mean someone won't pass something else to the server.

I don't recall much VBScript, but maybe this would work:
sql = "SELECT * FROM myTable WHERE id=" &
CInt(Request.QueryString("id")).toNumber().toString()

...or to be on the safe side, make it a function:
clean_id_str = sanitizeID(CInt(Request.QueryString("id")))
sql = "SELECT * FROM myTable WHERE id=" & clean_id_str

But you're correct that for data retrieval, as long as you make sure the id
is an integer, your method will always work and can be secure for queries
where you are selecting on an integer column, as long as you make sure what
you put in the sql statement is just numeric.


Generally speaking though, I personally prefer having one consistent,
standard solution for database interaction within a specific application,
like those mentioned by others on the list, that work for both data
retrieval and data manipulation.  Robert Nilsen mentioned "prepared
statements, a.k.a. bind variables/parameters," which if you've ever used
perl/DBI/DBD to access a database like mysql, works great, and you don't
even have to think about security, just remember to pass any variables in as
bind variables.  Here's an example:
        use DBI;
        $dbh = DBI->connect("DBI:$dbsystem:$dbname", $dbuser, $dbpass);
        $sth = $dbh->prepare("INSERT INTO contacts (name,email) VALUES
(?,?)");
        $sth->execute($name,$email);

Some people mentioned that if you use prepared statements "you lose
compatibility with different database systems."  If I understand DBI
correctly, it was designed so the code written above will work with any
database with only one modification: updating the global variable $dbsystem
from "mysql" to "oracle" for example.  Of course if you the database you're
switching to has different "features" than the one you're switching from,
there's nothing DBI can do to help you with that.

So I would go so far as to say using DBI's prepared statements for database
interaction is considered a "best practice" for securely accessing a
database in perl.  I'm curious if there's a central repository of other such
"best practices" for other languages (ASP, java, PHP, etc.).  I went to
http://www.owasp.org/filters/ as suggested, hoping it would have that
information, but all I found was a brief description of the project and a
note that indicates the alpha release of the draft plan for the project was
expected in late 2002.  Is it worth installing cvs to see what's in there?

Thanks,
-Jim


----- Original Message -----
From: "Mark Mcdonald" <m.mcdonald () cgl com au>
To: "'Ken Anderson'" <ka () pacific net>
Cc: <webappsec () securityfocus com>
Sent: Tuesday, February 11, 2003 4:44 PM
Subject: RE: SQL Injection Basics


> My personal favourite method when working with IIS/ASP is to handle all
data
> .retrieval. using only the primary key, which is always an integer.
> Fortunately, digits do not pose a security threat in any way shape or
form.
> in VBScript/ASP,
>
> sql = "SELECT * FROM myTable WHERE id=" & CInt(Request.QueryString("id"))
>
> > From my experience, this is unbeatable.  However there is one obvious,
> fairly big drawback - it only works on integers - hence why it is only
used
> for retrieval.
>
> Mark.
>
> -----Original Message-----
> From: Ken Anderson [mailto:ka () pacific net]
> Sent: Wednesday, February 12, 2003 4:21 AM
> Cc: webappsec () securityfocus com
> Subject: Re: SQL Injection Basics
>
>
>
> With mysql, you can use double quotes instead of single quotes around
> strings. http://www.mysql.com/doc/en/Extensions_to_ANSI.html
> You can then allow single quotes in user input for things like last name
> of "O'Malley"
>
> in java:
>
> foo = req.getParameter("foo");
> sanitize(foo); // disallow other bad stuff [%()"\...]
> sql = "select * from users where username = "\"+foo+"\"";
>
> If the value of foo is "'foo", it's not a problem.
>
> mysql> select lastname from users where lastname = "O'Brien";
> +--------------+
> | lastname     |
> +--------------+
> | O'Brien      |
> | O'Brien      |
> +--------------+
>
> Ken A.
>
>
> dreamwvr () dreamwvr com wrote:
> > On Tue, Feb 11, 2003 at 04:35:50PM +0100, Sverre H. Huseby wrote:
> >
> > > Consider a system talking to PostgreSQL (or MySQL or any other
> > > database that accepts C-style backslash escapes in string constants).
> > > If the developer just thinks about the ticks, he may (given
> >
> > Well IMO why not simply filter out all non alpha and integers.
> > logging everything else and not allowing to form a SQL statement
> > at all? Then allow very select special characters like ; only in
> > a specific position. Just my 2 cents.
> >
> > Best Regards,
> > dreamwvr () dreamwvr com
>
>
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