CVE-2024-43368: Trix has a cross-site Scripting vulnerability on copy & paste

The Trix editor, versions prior to 2.1.4, is vulnerable to XSS when pasting malicious code. This vulnerability is a bypass of the fix put in place for https://github.com/basecamp/trix/security/advisories/GHSA-qjqp-xr96-cj99. In https://github.com/basecamp/trix/pull/1149, we added sanitation for Trix attachments with a text/html content type. However, Trix only checks the content type on the paste event’s dataTransfer object. As long as the dataTransfer has a content type of text/html, Trix parses its contents and creates an Attachment with them, even if the attachment itself doesn’t have a text/html content type. Trix then uses the attachment content to set the attachment element’s innerHTML.