GHSA-x82r-6j37-vrgg Pimcore's Admin Classic Bundle allows HTML Injection

• Packagist pimcore/admin-ui-classic-bundle: < 1.7.6 → fixed in 1.7.6

Summary An HTML injection issue allows users with access to the email sending functionality to inject arbitrary HTML code into emails sent via the admin interface, potentially leading to session cookie theft and the alteration of page content. Details The vulnerability was discovered in the `/admin/email/send-test-email` endpoint using the `POST` method. The vulnerable parameter is `content`, which permits the injection of arbitrary HTML code during the email sending process. While JavaScript code injection is blocked through filtering, HTML code injection remains possible. PoC To reproduce the vulnerability, a user must fill out the email's content form with the desired HTML payload. Impact This HTML injection vulnerability can potentially enable phishing attacks by allowing the insertion of any html like fake login forms, etc. All functionalities that process user input should be carefully reviewed to ensure that data is appropriately encoded as HTML entities in server responses. For instance, a reflected input paramete like ` just a test ` should be displayed in the HTML response as `&#x3c;h1&#x3e; just a test &#x3c;/h1&#x3e; &#x3c;p&#x3e; &#x3c;img&#x3e;`.