CVE-2026-27156 — NiceGUI has XSS via Code Injection

Affected: zauberzeug nicegui

NiceGUI is a Python-based UI framework. Prior to version 3.8.0, 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. Version 3.8.0 contains a fix.

GHSA-78qv-3mpx-9cqq — NiceGUI vulnerable to XSS via Code Injection during client-side element function execution

Affected: PyPI: nicegui

### 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…

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CVE-2026-27156 — NiceGUI has XSS via Code Injection

GHSA-78qv-3mpx-9cqq — NiceGUI vulnerable to XSS via Code Injection during client-side element function execution