CVE-2026-27156: Nicegui Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-78qv-3mpx-9cqq",
  "modified" : "2026-03-06T19:51:35Z",
  "published" : "2026-02-24T19:56:18Z",
  "aliases" : [ "CVE-2026-27156" ],
  "summary" : "NiceGUI vulnerable to XSS via Code Injection during client-side element function execution",
  "details" : "### Summary\n\nSeveral 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.\n\nAdditionally, `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.\n\n### Attack Vector\n\nAn 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()`.\n\n**Example:** `/?method=alert(document.cookie)` combined with application code like:\n```python\nelement.run_method(user_provided_method_name)\n```\n\n### Impact\n\n- Cookie/token theft\n- DOM manipulation (phishing, fake login forms)\n- Actions performed as the victim user\n\n### Affected Methods\n\n1. `Element.run_method()`\n2. `Element.get_computed_prop()`\n3. `AgGrid.run_grid_method()`\n4. `AgGrid.run_row_method()`\n5. `EChart.run_chart_method()`\n6. `JsonEditor.run_editor_method()`\n7. `Xterm.run_terminal_method()`\n8. `Leaflet.run_map_method()`\n9. `Leaflet.run_layer_method()`\n10. `LeafletLayer.run_method()`\n\n### Fix\n\n1. Use `json.dumps()` for proper escaping of method/property names in `run_method()` and `get_computed_prop()`\n2. 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\n\n### Migration\n\nCode that previously passed JavaScript functions as method names needs to use `ui.run_javascript()` instead:\n\n```python\n# Before:\nrow = await grid.run_grid_method('g => g.getDisplayedRowAtIndex(0).data')\n\n# After:\nrow = await ui.run_javascript(f'return getElement({grid.id}).api.getDisplayedRowAtIndex(0).data')\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "nicegui"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.8.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.7.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/security/advisories/GHSA-78qv-3mpx-9cqq"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27156"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/zauberzeug/nicegui/commit/1861f59cc374ca0dc9d970b157ef3774720f8dbf"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/zauberzeug/nicegui"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-24T19:56:18Z",
    "nvd_published_at" : "2026-02-24T18:29:33Z"
  }
}