Magento LTS vulnerable to Stored XSS via TinyMCE WYSIWYG Editor

Summary

From HackerOne report [#1948040](https://hackerone.com/reports/1948040) by Halit AKAYDIN (hltakydn) ### Impact _What kind of vulnerability is it? Who is impacted?_ The TinyMCE WYSIWYG editor fails to filter scripts when rendering the HTML in specially crafted HTML tags. ### Patches _Has the problem been patched? What versions should users upgrade to?_ This vulnerability was fixed in version 20.2.0 by upgrading TinyMCE to a recent version in https://github.com/OpenMage/magento-lts/pull/3220 ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_ The WYSIWYG editor features could be disabled in the configuration. Possibly some WAF appliances would filter this attack. ### References _Are there any links users can visit to find out more?_ The attack is simply an exploit of the "onmouseover" attribute of an `img` element as described on [OWASP XSS Filter Evasion](https://cheatsheetseries.owasp.org/cheatsheets/XSS_Filter_Evasion_Cheat_Sheet.html)