Chartbrew is an open-source web application that can connect directly to databases and APIs and use the data to create charts. In versions 4.9.0 through 5.0.0, an authenticated user with project-editor permissions can store arbitrary HTML/JavaScript in the `ChartDatasetConfig.legend` field. The payload is persisted verbatim in the database, propagated through the Chart.js rendering pipeline, and injected into the tooltip DOM element via an unguarded `innerHTML` assignment in `ChartTooltip.js`. Every unauthenticated viewer of the public dashboard triggers JavaScript execution on page load — no hover interaction is required. Browser-based Playwright verification confirmed `alert('localhost')` fires immediately and `<img src="x" onerror="alert(document.domain)">` is present in the `#chartjs-tooltip` DOM element. Version 5.0.1 contains a fix.