Impact

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). An example are anonymous comments in XWiki where the HTML macro filters HTML using restricted mode:

{{html}}
<a href='' onclick='alert(1)'>XSS</a>
{{/html}}

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.

Patches

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.

Workarounds

There are no known workarounds apart from upgrading to a version including the fix.

References

• b11eae9 - the patch with the filter
• 4a185e0 - the patch with the definitions what is allowed
• https://jira.xwiki.org/browse/XWIKI-9118 - the security issue with the HTML macro
• https://jira.xwiki.org/browse/XCOMMONS-1680 - the issue regarding a definition of what is allowed HTML
• https://jira.xwiki.org/browse/XCOMMONS-2426 - the issue regarding the filter that fixes the security issue

For more information

If you have any questions or comments about this advisory:

• Open an issue in Jira XWiki
• Email us at XWiki Security mailing-list