This carries on from the SQL injection article. The previous example was a slightly contorted result since I was using information that I knew about the database and the results returned were appearing in the page. I was just trying to introduce the concepts. Now here I’m introducing automated blind SQL injection. Source code for this article is avaiable in a zip file.
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Cross-Site Scripting (XSS) is a vulnerablity where an attacker can put their own code on your site. Often javascript is used so I’ll use it here in my examples.
Here’s a code example:
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Available for download is my WordPress HTML output filter (the HOF), a plugin for WordPress 2.9 (it might work with previous versions, it might require tweaking). WordPress installations on large-scale shared hosts have come under assault recently, as noted in the WordPress Development blog, not through any flaw in WordPress but flaws in the web hosts’ servers. Those of us who use such services can never be sure of how secure the server is.
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Suppose I have a feedback form on a webpage. Something like:
<form method="get" action="testmail.php">
Email: <input name="email" type="text" value="" />
<br />
Feedback: <textarea name="feedback"></textarea>
</form>
And suppose I deal with it in PHP a bit like this:
$from = '' .POST["email"];
$feedback = '' . $_POST["feedback"];
$rtn = mail('james@rootdev.com', "Feedback from website", $feedback, "From: " . $from);
What could possibly go wrong?
Quite a lot.
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I’m going to create the worst blogging software in the world, consisting of a single web page displaying a list of comments and where users can post new comments or search for comments. The data will be stored in a MySQL database. The site is going to have horrendous security flaws (on purpose). Then I’m going to hack it’s innermost secrets just through the web page. Then I’ll show you how to make it secure.