CVE-2026-27156
MEDIUM6.1EPSS 0.05%NiceGUI vulnerable to XSS via Code Injection during client-side element function execution
Description
### Summary 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. ### Attack Vector 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: ```python element.run_method(user_provided_method_name) ``` ### Impact - Cookie/token theft - DOM manipulation (phishing, fake login forms) - Actions performed as the victim user ### Affected Methods 1. `Element.run_method()` 2. `Element.get_computed_prop()` 3. `AgGrid.run_grid_method()` 4. `AgGrid.run_row_method()` 5. `EChart.run_chart_method()` 6. `JsonEditor.run_editor_method()` 7. `Xterm.run_terminal_method()` 8. `Leaflet.run_map_method()` 9. `Leaflet.run_layer_method()` 10. `LeafletLayer.run_method()` ### Fix 1. Use `json.dumps()` for proper escaping of method/property names in `run_method()` and `get_computed_prop()` 2. Remove the `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 JavaScript ### Migration Code that previously passed JavaScript functions as method names needs to use `ui.run_javascript()` instead: ```python # 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') ```
Affected packages (1)
- PyPI/niceguifrom 0, < 3.8.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |