Several NiceGUI APIs that execute methods on client-side elements (Element.run_method(), AgGrid.run_grid_method(), EChart.run_chart_method(), and others) use an eval() fallback in the JavaScript-side runMethod() function. When user-controlled input is passed as the method name, an attacker can inject arbitrary JavaScript that executes in the victim's browser.
Additionally, Element.run_method() and Element.get_computed_prop() used string interpolation instead of json.dumps() for the method/property name, allowing quote injection to break out of the intended string context.
An attacker crafts a malicious URL with a payload as a query parameter. If the application passes this parameter as a method name to any of the affected APIs, the payload is sent to the client via WebSocket and executed via eval().
Example: /?method=alert(document.cookie) combined with application code like:
element.run_method(user_provided_method_name)
Element.run_method()Element.get_computed_prop()AgGrid.run_grid_method()AgGrid.run_row_method()EChart.run_chart_method()JsonEditor.run_editor_method()Xterm.run_terminal_method()Leaflet.run_map_method()Leaflet.run_layer_method()LeafletLayer.run_method()json.dumps() for proper escaping of method/property names in run_method() and get_computed_prop()eval() fallback from runMethod() in nicegui.js — method names that are not found on the element now raise an error instead of being evaluated as arbitrary JavaScriptCode that previously passed JavaScript functions as method names needs to use ui.run_javascript() instead:
# Before:
row = await grid.run_grid_method('g => g.getDisplayedRowAtIndex(0).data')
# After:
row = await ui.run_javascript(f'return getElement({grid.id}).api.getDisplayedRowAtIndex(0).data')
{
"nvd_published_at": "2026-02-24T18:29:33Z",
"github_reviewed_at": "2026-02-24T19:56:18Z",
"github_reviewed": true,
"cwe_ids": [
"CWE-79"
],
"severity": "MODERATE"
}