XWiki Commons are technical libraries common to several other top level XWiki projects. The "restricted" mode of the HTML cleaner in XWiki, introduced in version 4.2-milestone-1, only escaped <script> and <style>-tags but neither attributes that can be used to inject scripts nor other dangerous HTML tags like <iframe>. As a consequence, any code relying on this "restricted" mode for security is vulnerable to JavaScript injection ("cross-site scripting"/XSS). When a privileged user with programming rights visits such a comment in XWiki, the malicious JavaScript code is executed in the context of the user session. This allows server-side code execution with programming rights, impacting the confidentiality, integrity and availability of the XWiki instance. This problem has been patched in XWiki 14.6 RC1 with the introduction of a filter with allowed HTML elements and attributes that is enabled in restricted mode. There are no known workarounds apart from upgrading to a version including the fix.