Rocket.Chat 6.12.0, 6.11.2, 6.10.5, 6.9.6, 6.8.6, 6.7.8, and earlier allows stored XSS in the description and release notes of the marketplace and private apps.
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.