Rocket.Chat: Missing URL protocol sanitization in ImageElement allows javascript: URLs in markdown images

Rocket.Chat is an open-source, secure, fully customizable communications platform. Prior to 8.5.0, the ImageElement component in packages/gazzodown renders user-controlled src values directly into and attributes without protocol sanitization. Unlike the analogous LinkSpan component — which uses sanitizeUrl to block javascript:, data:, and vbscript: protocols — ImageElement passes the raw URL through unchanged. An authenticated user can post a markdown image with a javascript: URL that, if clicked on an older browser, would execute arbitrary JavaScript in the viewer's session. This vulnerability is fixed in 8.5.0.