A friend of mine posed a question: Do you know of any good PHP based vulnerability scanners? I told him I did not (add any in the comments, if you know! 
) – but it wouldn’t be that hard to build one. He asked me to give him a code example, so here goes:
The Goals
I have only 2 goals to accomplish with this quick script:
- Should handle multiple forms on a web page
- Should be able to submit a payload and automatically review if it is shown unfiltered.
Since this is just a quick script, we do know a few things however:
- It will not handle javascript based forms that set the action to something different.
- It doesn’t specifically help identify which form field is the vulnerable one.
But with that, its not that bad.
The example website we’re reviewing
I have two really simple pages for our test site, the form itself and the ‘login’ page.
testform.html
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | <html> <head> <title>Test Login Form, yo</title> </head> <body> <h1>Oh HAI!</h1> <p>Login or no?</p> <form action='http://localhost/testsubmit.php' method='post' name='login'> Username: <input type="text" name="username" /><br /> Password: <input type="password" name="password" /><br /> <input type="submit" /> </form> </body> </html> |
testsubmit.php
1 2 3 4 5 6 7 8 | <?php if ($_POST['username'] == 'MYUSER' && $_POST['password'] == 'MYPASS') { print 'you have logged in'; } else { print "{$_POST['username']} did not authenticate correctly."; } ?> |
As you can see, if the login credentials are not correct, it prints the unfiltered username onto the screen. Obviously, this is a very simple example.
The PHP Script
The comments should help the interpretation of this script, so I won’t ramble…
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 | <?php /** set target, payload **/ $target = 'http://localhost/testform.html'; $payload = '<script>alert("word!");</script>'; /** get content, create dom document with it **/ $targetContent = file_get_contents($target); $doc = new DomDocument(); $doc->loadHTML($targetContent); /** get all the forms, iterate through each **/ $forms = $doc->getElementsByTagName('form'); foreach ($forms as $form) { $submitInputs = array(); $submitTo = $form->getAttribute('action') ? $form->getAttribute('action') : $target; $submitMethod = $form->getAttribute('method') ? $form->getAttribute('method') : 'GET'; /** get all inputs so we can set the values **/ $tagsToParse = array('input', 'textarea'); foreach ($tagsToParse as $tag) { $retrieved = $form->getElementsByTagName($tag); foreach ($retrieved as $item) { /** get the value - we want to retain whats in there just in case... **/ $value = $item->getAttribute('value') ? $item->getAttribute('value') : ''; $value .= $payload; $submitInputs[$item->getAttribute('name')] = $value; } } print '<h2>Submitting payload to form: ' . $form->getAttribute('name') . '</h2>'; /** got our content, prepare for submission, get submitted content **/ $opts = array('http'=>array('method'=>strtoupper($submitMethod), 'header'=>'Content-Type: application/x-www-form-urlencoded', 'content'=>http_build_query($submitInputs))); $context = stream_context_create($opts); $submittedFormContents = file_get_contents($submitTo, false, $context); /** find the payload ? **/ $count = substr_count($submittedFormContents, $payload); print "Times payload found: {$count}<br />"; } |
As you can see, still very simple, but it lays the groundwork. Combine this with my link checking code and you could make a pretty decent start on a PHP vulnerability scanner.