A recently-discovered vulnerability in Firefox (CVE-2022-22755) could leave users exposed to potential malicious web activity. The vulnerability could allow an attacker to execute persistent JavaScript after a user had closed their browser tab. This blog post will discuss the details of the vulnerability, including the potential dangers, as well as provide a code snippet, original references, and steps for mitigating the issue.

The vulnerability

CVE-2022-22755 primarily affects Firefox versions earlier than 97. The issue revolves around the use of XSL Transforms, which are a method used to generate stylized HTML or XML (often as part of a visual rendering) based on an XML document and an accompanying XSL style sheet.

Within the affected versions of Firefox, when a malicious webserver serves an XSL document containing JavaScript code, the JavaScript would continue to execute even after the user closed the browser tab. This persistence breaks standard browsing security protocols and, under specific circumstances, could be dangerous to end users.

The exploit

To exploit this vulnerability, an attacker would need to serve an XSL Transform, then somehow force a user to visit the malicious web page. The following code snippet provides an example of the XSL containing JavaScript code:

<?xml version="1." encoding="UTF-8"?>
<xsl:stylesheet version="1." xmlns:xsl="http://www.w3.org/1999/XSL/Transform">;
  <xsl:output method="html" indent="yes"/>
  <xsl:template match="/">
    <html>
      <head>
        <script>
          function executeJavaScript() {
            // Insert malicious JavaScript code here
          }
          executeJavaScript();
        </script>
      </head>
      <body>
        <h1>Malicious Webpage</h1>
      </body>
    </html>
  </xsl:template>
</xsl:stylesheet>

This XSL Transform demonstrates the malicious JavaScript code embedded within the document. When the user navigates to the server hosting this document, the JavaScript will execute and persist even if the tab is closed.

For more information and original references about this vulnerability, you can refer to

1. Mozilla Firefox Security Advisory: https://www.mozilla.org/en-US/security/advisories/mfsa2022-07/#CVE-2022-22755
2. CVE-2022-22755: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-22755
3. XSL Transform Tutorial: https://www.w3schools.com/xml/xsl_intro.asp

Mitigation

The developers at Mozilla have already addressed this issue in Firefox version 97, released on February 8, 2022. To protect yourself and your browsing sessions, follow the steps outlined below:

1. Update to the latest version of Firefox by visiting https://www.mozilla.org/en-US/firefox/new/ or using the automatic update feature within the browser.
2. Always be cautious about clicking on links from unknown sources or navigating to unfamiliar websites.

Install and maintain an up-to-date antivirus solution to scan websites and downloaded files.

4. Consider using privacy and security extensions, such as NoScript, to help block unwanted content and scripts.

Conclusion

CVE-2022-22755 susceptibility to malicious JavaScript execution on the Firefox web browser highlights the importance of keeping browsers up to date and taking precautions while browsing. By updating to Firefox 97 and following the steps mentioned above, users can safeguard themselves against this vulnerability and maintain a secure browsing environment.

Timeline

Published on: 12/22/2022 20:15:00 UTC
Last modified on: 12/29/2022 23:08:00 UTC