CVE-2021-28114: 
PHP vulnerability analysis and mitigation

Froala WYSIWYG Editor version 3.2.6-1 and earlier versions were affected by a cross-site scripting (XSS) vulnerability due to a namespace confusion during HTML parsing. The vulnerability was discovered on February 26, 2021, and was assigned CVE-2021-28114. This security flaw affected approximately 30,000 websites that utilized the Froala editor, a lightweight What-You-See-Is-What-You-Get HTML rich text editor for developers and content creators (Bishop Fox, ZDNET).

The vulnerability stems from a confusion during the HTML parsing sequence. The $$ tag causes the parser to switch its namespace context from HTML to MathML, which processes differently than HTML. The tag and embedded HTML comment causes the parser to switch context during the tokenization phase of HTML parsing and read the strings that follow as user data (RCDATA) rather than computer instructions. This parsing confusion allows attackers to bypass existing XSS protections by inserting JavaScript payloads in HTML event handlers within specific HTML and MathML tags (ZDNET, Bishop Fox).

The vulnerability's impact varies depending on the implementation context. It could manifest as either stored or reflected XSS, potentially allowing attackers to control affected sites' user experience, force unauthorized actions on behalf of users (such as bank transfers in worst-case scenarios), escalate privileges, or exfiltrate sensitive data. The severity of the impact is contingent on how Froala is implemented within the application and whether users can control content inside the editor (Bishop Fox).

The vendor released a patch in version 3.2.7 on May 18, 2021. Users are advised to upgrade to at least version 3.2.7 and leverage the Full Feature configuration of the editor, as other configurations such as Full Page remained unpatched at the time of the advisory. Version 4.0, released on June 1, 2021, is also available as a more recent update (ZDNET, Bishop Fox).