tinymce is an open source rich text editor. A cross-site scripting (XSS) vulnerability was discovered in the alert and confirm dialogs when these dialogs were provided with malicious HTML content. This can occur in plugins that use the alert or confirm dialogs, such as in the image plugin, which presents these dialogs when certain errors occur. The vulnerability allowed arbitrary JavaScript execution when an alert presented in the TinyMCE UI for the current user. This vulnerability has been patched in TinyMCE 5.10.7 and TinyMCE 6.3.1 by ensuring HTML sanitization was still performed after unwrapping invalid elements. Users are advised to upgrade to either 5.10.7 or 6.3.1. Users unable to upgrade may ensure the the imagesuploadhandler returns a valid value as per the imagesuploadhandler documentation.

Impact A mutation cross-site scripting (mXSS) vulnerability was discovered in TinyMCE’s core undo and redo functionality. When a carefully-crafted HTML snippet passes the XSS sanitisation layer, it is manipulated as a string by internal trimming functions before being stored in the undo stack. If the HTML snippet is restored from the undo stack, the combination of the string manipulation and reparative parsing by either the browser's native DOMParser API (TinyMCE 6) or the SaxParser API (TinyMCE 5) mutates the HTML maliciously, allowing an XSS payload to be executed. ​This vulnerability also impacts these related TinyMCE APIs and plugins:​ tinymce.Editor.getContent({ format: 'raw' }) tinymce.Editor.resetContent() Autosave Plugin

Patches This vulnerability has been patched in TinyMCE 5.10.8 and TinyMCE 6.7.1 by ensuring HTML is trimmed using node-level manipulation instead of string manipulation.

Fix To avoid this vulnerability: Upgrade to TinyMCE 5.10.8 or higher for TinyMCE 5.x. Upgrade to TinyMCE 6.7.1 or higher for TinyMCE 6.x.

Acknowledgements Tiny Technologies would like to thank Masato Kinugawa of Cure53 for discovering this vulnerability.

References TinyMCE 5.10.8 Release Notes TinyMCE 6.7.1 Release Notes

For more information If you have any questions or comments about this advisory: Email us at <infosec@tiny.cloud> Open an issue in the TinyMCE repo

Impact A cross-site scripting (XSS) vulnerability was discovered in TinyMCE’s Notification Manager API. The vulnerability exploits TinyMCE's unfiltered notification system, which is used in error handling. The conditions for this exploit requires carefully crafted malicious content to have been inserted into the editor and a notification to have been triggered.

When a notification was opened, the HTML within the text argument was displayed unfiltered in the notification. The vulnerability allowed arbitrary JavaScript execution when an notification presented in the TinyMCE UI for the current user. This issue could also be exploited by any integration which uses a TinyMCE notification to display unfiltered HTML content.

Patches This vulnerability has been patched in TinyMCE 5.10.8 and TinyMCE 6.7.1 by ensuring that the HTML displayed in the notification is sanitized, preventing the exploit.

Fix To avoid this vulnerability:

Upgrade to TinyMCE 5.10.8 or higher for TinyMCE 5.x. Upgrade to TinyMCE 6.7.1 or higher for TinyMCE 6.x.

References <https://tiny.cloud/docs/release-notes/release-notes5108/#securityfixes> <https://tiny.cloud/docs/tinymce/6/6.7.1-release-notes/#security-fixes>

For more information If you have any questions or comments about this advisory: Email us at <infosec@tiny.cloud> Open an issue in the TinyMCE repo

Impact A mutation cross-site scripting (mXSS) vulnerability was discovered in TinyMCE’s core undo/redo functionality and other APIs and plugins. Text nodes within specific parents are not escaped upon serialization according to the HTML standard. If such text nodes contain a special character reserved as an internal marker, they can be combined with other HTML patterns to form malicious snippets. These snippets pass the initial sanitisation layer when the content is parsed into the editor body, but can trigger XSS when the special internal marker is removed from the content and re-parsed. Such mutations occur when serialised HTML content is processed before being stored in the undo stack, or when the following APIs and plugins are used: tinymce.Editor.getContent({ format: 'raw' }) tinymce.Editor.resetContent() Autosave Plugin

Patches This vulnerability has been patched in TinyMCE 6.7.3 by: ensuring that any unescaped text nodes which contain the special internal marker are emptied before removing the marker from the rest of the HTML, and removing the special internal marker from content strings passed to Editor.setContent, Editor.insertContent, and Editor.resetContent APIs to prevent them from being loaded into the editor as user-provided content.

Fix To avoid this vulnerability: - Upgrade to TinyMCE 6.7.3 or higher for TinyMCE 6.x. - Upgrade to TinyMCE 5.10.9 or higher for TinyMCE 5.x.

Acknowledgements Tiny Technologies would like to thank Masato Kinugawa of Cure53 for discovering this vulnerability.

References - TinyMCE 5.10.9 Release Notes - TinyMCE 6.7.3 Release Notes

For more information

Email us at infosec@tiny.cloud Open an issue in the TinyMCE repo