CSRF/stored XSS in Quiz And Survey Master (Formerly Quiz Master Next) allows unauthenticated attackers to do almost anything an admin can

Score Vector Complexity Authentication Confidentiality Integrity Availability
5.8
Medium
Network Medium None Partial Partial None

You can read more about CVSS base scores on Wikipedia or in the CVSS specification.

Vulnerability

A CSRF vulnerability allows an unauthenticated attacker to add questions to existing quizzes.

The question_name parameter is put into a manually-constructed JavaScript object and escaped with esc_js() (php/qmn_options_questions_tab.php line 499). If the user (or attacker) creates a new question on a quiz containing “<script>alert(1)</script>” in the question_name field then “question: ‘&lt;script&gt;alert(1)&lt;/script&gt;’,” will get output inside the JS object. All good so far.

However, in js/admin_question.js on line 205, we see this line, as part of some JS-generated HTML:

jQuery('<textarea/>').html(questions_list[i].question.replace(/"/g, '"').replace(/'/g, "'")).text()+

This looks okay. We’re creating a TEXTAREA element, setting its HTML to the value of the question_name parameter, and extracting the .text() of it. If we did jQuery(‘<textarea/>’).html(‘<script>alert(1)</script>’).text() we would get “alert(1)” as the output.

However, that’s not how inline JavaScript gets parsed. Between a <script> and a </script>, the HTML parser actually parses “&lt;” as “&lt;” not as “<“. So if we do jQuery(‘<textarea/>’).html(‘&lt;script&gt;alert(1)&lt;/script&gt;’).text() we get “<script>alert(1)</script>”.

And since “<script>alert(1)</script>” doesn’t appear anywhere in the page, Chrome’s reflected XSS mitigation measures are not activated. Thus the stored XSS attack can be executed immediately.

Proof of concept

Click the submit button on the following page (in a real attack the form can be submitted without user interaction):

<form method="POST" action="http://localhost/wp-admin/admin.php?page=mlw_quiz_options&quiz_id=1">
<input type="text" name="question_type" value="0">
<input type="text" name="question_name" value="&lt;script>alert(1)&lt;/script>">
<input type="text" name="question_submission" value="new_question">
<input type="text" name="quiz_id" value="1">
<input type="submit">
</form>

Mitigation/further actions

Upgrade to version 4.7.9 or later.