fix: harden trust-bearing window globals and gate script loading (#9330)

Follow-up to #9318. Extends the frozen first-party marker pattern to
`__MARIMO_STATIC__` (backs the virtual-file allowlist) and
`__MARIMO_MOUNT_CONFIG__`, and adds a shared
`hasTrustedNotebookContext()`
predicate so `RenderHTML.replaceSrcScripts` refuses notebook-authored
`<script src>` in untrusted edit mode before any user interaction.

Author: mscolnick

frontend/index.html

@@ -72,7 +72,11 @@
     <!-- This is a portal for the data editor to render in -->
     <div id="portal" data-testid="glide-portal" style="position: fixed; left: 0; top: 0; z-index: 9999"></div>
     <script data-marimo="true">
-      window.__MARIMO_MOUNT_CONFIG__ = '{{ mount_config }}';
+      Object.defineProperty(window, "__MARIMO_MOUNT_CONFIG__", {
+        value: Object.freeze('{{ mount_config }}'),
+        writable: false,
+        configurable: false,
+      });
     </script>
     <script type="module" src="/src/main.tsx"></script>
   </body>

frontend/src/core/static/__tests__/export-context.test.ts

@@ -0,0 +1,122 @@
+/* Copyright 2026 Marimo. All rights reserved. */
+// @vitest-environment jsdom
+
+import type { ExtractAtomValue } from "jotai";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { hasRunAnyCellAtom } from "@/components/editor/cell/useRunCells";
+import { userConfigAtom } from "@/core/config/config";
+import { parseUserConfig } from "@/core/config/config-schema";
+import { initialModeAtom } from "@/core/mode";
+import { store } from "@/core/state/jotai";
+import {
+  getMarimoExportContext,
+  hasTrustedExportContext,
+  hasTrustedNotebookContext,
+} from "../export-context";
+
+type ExportContextWindow = Window & {
+  __MARIMO_EXPORT_CONTEXT__?: {
+    trusted: boolean;
+    notebookCode?: string;
+  };
+};
+
+function setAutoInstantiate(value: boolean) {
+  const cleared = parseUserConfig({});
+  store.set(userConfigAtom, {
+    ...cleared,
+    runtime: { ...cleared.runtime, auto_instantiate: value },
+  });
+}
+
+describe("hasTrustedNotebookContext", () => {
+  let previousHasRunAnyCell: ExtractAtomValue<typeof hasRunAnyCellAtom>;
+  let previousConfig: ExtractAtomValue<typeof userConfigAtom>;
+  let previousMode: ExtractAtomValue<typeof initialModeAtom>;
+  let w: ExportContextWindow;
+
+  beforeEach(() => {
+    w = window as ExportContextWindow;
+    previousHasRunAnyCell = store.get(hasRunAnyCellAtom);
+    previousConfig = store.get(userConfigAtom);
+    previousMode = store.get(initialModeAtom);
+    store.set(hasRunAnyCellAtom, false);
+    setAutoInstantiate(false);
+    store.set(initialModeAtom, "edit");
+    delete w.__MARIMO_EXPORT_CONTEXT__;
+  });
+
+  afterEach(() => {
+    store.set(hasRunAnyCellAtom, previousHasRunAnyCell);
+    store.set(userConfigAtom, previousConfig);
+    store.set(initialModeAtom, previousMode);
+    delete w.__MARIMO_EXPORT_CONTEXT__;
+  });
+
+  it("returns false in untrusted edit mode before interaction", () => {
+    expect(hasTrustedNotebookContext()).toBe(false);
+  });
+
+  it("returns true once the user has run a cell", () => {
+    store.set(hasRunAnyCellAtom, true);
+    expect(hasTrustedNotebookContext()).toBe(true);
+  });
+
+  it("returns true when a trusted export context is installed", () => {
+    w.__MARIMO_EXPORT_CONTEXT__ = { trusted: true };
+    expect(hasTrustedNotebookContext()).toBe(true);
+  });
+
+  it("returns true when auto_instantiate is enabled", () => {
+    setAutoInstantiate(true);
+    expect(hasTrustedNotebookContext()).toBe(true);
+  });
+
+  it("returns true in read mode", () => {
+    store.set(initialModeAtom, "read");
+    expect(hasTrustedNotebookContext()).toBe(true);
+  });
+
+  it("returns false if initialMode throws (config not yet applied)", () => {
+    store.set(initialModeAtom, undefined);
+    expect(hasTrustedNotebookContext()).toBe(false);
+  });
+});
+
+describe("hasTrustedExportContext / getMarimoExportContext shape validation", () => {
+  let w: ExportContextWindow;
+
+  beforeEach(() => {
+    w = window as ExportContextWindow;
+    delete w.__MARIMO_EXPORT_CONTEXT__;
+  });
+
+  afterEach(() => {
+    delete w.__MARIMO_EXPORT_CONTEXT__;
+  });
+
+  it("accepts a valid context", () => {
+    w.__MARIMO_EXPORT_CONTEXT__ = { trusted: true, notebookCode: "x = 1" };
+    expect(hasTrustedExportContext()).toBe(true);
+    expect(getMarimoExportContext()).toEqual({
+      trusted: true,
+      notebookCode: "x = 1",
+    });
+  });
+
+  it("rejects a context where `trusted` is not exactly true", () => {
+    w.__MARIMO_EXPORT_CONTEXT__ = {
+      trusted: "yes" as unknown as true,
+    };
+    expect(hasTrustedExportContext()).toBe(false);
+    expect(getMarimoExportContext()).toBeUndefined();
+  });
+
+  it("rejects a context with non-string notebookCode", () => {
+    w.__MARIMO_EXPORT_CONTEXT__ = {
+      trusted: true,
+      notebookCode: 42 as unknown as string,
+    };
+    expect(getMarimoExportContext()).toBeUndefined();
+  });
+});

frontend/src/core/static/__tests__/static-state.test.ts

@@ -0,0 +1,80 @@
+/* Copyright 2026 Marimo. All rights reserved. */
+// @vitest-environment jsdom
+
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import {
+  getStaticModelNotifications,
+  getStaticVirtualFiles,
+  isStaticNotebook,
+} from "../static-state";
+
+function setMarimoStatic(value: unknown): void {
+  (window as unknown as { __MARIMO_STATIC__?: unknown }).__MARIMO_STATIC__ =
+    value;
+}
+
+function clearMarimoStatic(): void {
+  delete (window as unknown as { __MARIMO_STATIC__?: unknown })
+    .__MARIMO_STATIC__;
+}
+
+describe("static-state shape validation", () => {
+  beforeEach(() => {
+    clearMarimoStatic();
+  });
+
+  afterEach(() => {
+    clearMarimoStatic();
+  });
+
+  it("treats an absent global as not-a-static-notebook", () => {
+    expect(isStaticNotebook()).toBe(false);
+    expect(getStaticModelNotifications()).toBeUndefined();
+  });
+
+  it("accepts a well-formed state", () => {
+    setMarimoStatic({
+      files: { "/@file/a.txt": "data:text/plain;base64,YQ==" },
+      modelNotifications: [],
+    });
+    expect(isStaticNotebook()).toBe(true);
+    expect(getStaticVirtualFiles()).toEqual({
+      "/@file/a.txt": "data:text/plain;base64,YQ==",
+    });
+    expect(getStaticModelNotifications()).toEqual([]);
+  });
+
+  it("rejects a malformed global (missing files)", () => {
+    setMarimoStatic({ modelNotifications: [] });
+    expect(isStaticNotebook()).toBe(false);
+    expect(getStaticModelNotifications()).toBeUndefined();
+  });
+
+  it("rejects a malformed global (non-array modelNotifications)", () => {
+    setMarimoStatic({ files: {}, modelNotifications: "oops" });
+    expect(isStaticNotebook()).toBe(false);
+  });
+
+  it("rejects a non-object global", () => {
+    setMarimoStatic("pwned");
+    expect(isStaticNotebook()).toBe(false);
+  });
+
+  it("rejects an array as the state", () => {
+    setMarimoStatic([]);
+    expect(isStaticNotebook()).toBe(false);
+  });
+
+  it("rejects files when it is an array", () => {
+    setMarimoStatic({ files: [], modelNotifications: [] });
+    expect(isStaticNotebook()).toBe(false);
+  });
+
+  it("rejects files that contain non-string values", () => {
+    setMarimoStatic({
+      files: { "/@file/a.txt": 42 },
+      modelNotifications: [],
+    });
+    expect(isStaticNotebook()).toBe(false);
+  });
+});

frontend/src/core/static/export-context.ts

@@ -1,5 +1,10 @@
 /* Copyright 2026 Marimo. All rights reserved. */
 
+import { hasRunAnyCellAtom } from "@/components/editor/cell/useRunCells";
+import { autoInstantiateAtom } from "@/core/config/config";
+import { getInitialAppMode } from "@/core/mode";
+import { store } from "@/core/state/jotai";
+
 export interface MarimoExportContext {
   trusted: true;
   notebookCode?: string;
@@ -41,3 +46,39 @@ export function getMarimoExportContext():
 export function hasTrustedExportContext(): boolean {
   return getMarimoExportContext()?.trusted === true;
 }
+
+/**
+ * True when the current page is a context where notebook-authored script
+ * execution is expected, and therefore the user has consented (explicitly or
+ * by the nature of the page) to running arbitrary notebook content:
+ *
+ * - the user has run at least one cell, OR
+ * - a first-party exported notebook page installed a trusted export context
+ *   (islands / static exports / Quarto islands), OR
+ * - `auto_instantiate` is enabled (the notebook runs on page load by user
+ *   configuration), OR
+ * - the page was loaded in `read` / app mode (served by marimo as an app).
+ *
+ * Edit mode before any user interaction is intentionally NOT trusted — that
+ * is the only surface where we must prevent notebook-authored content from
+ * loading scripts or bypassing HTML sanitization.
+ */
+export function hasTrustedNotebookContext(): boolean {
+  if (store.get(hasRunAnyCellAtom)) {
+    return true;
+  }
+  if (hasTrustedExportContext()) {
+    return true;
+  }
+  if (store.get(autoInstantiateAtom)) {
+    return true;
+  }
+  try {
+    if (getInitialAppMode() === "read") {
+      return true;
+    }
+  } catch {
+    // getInitialAppMode throws before mount config is applied; treat as untrusted.
+  }
+  return false;
+}

frontend/src/core/static/static-state.ts

@@ -5,20 +5,58 @@ import type { MarimoStaticState, StaticVirtualFiles } from "./types";
 
 declare global {
   interface Window {
-    __MARIMO_STATIC__?: MarimoStaticState;
+    __MARIMO_STATIC__?: Readonly<MarimoStaticState>;
   }
 }
 
+function isStringToStringRecord(
+  value: unknown,
+): value is Record<string, string> {
+  if (typeof value !== "object" || value === null || Array.isArray(value)) {
+    return false;
+  }
+  for (const entry of Object.values(value)) {
+    if (typeof entry !== "string") {
+      return false;
+    }
+  }
+  return true;
+}
+
+function isMarimoStaticState(
+  value: unknown,
+): value is Readonly<MarimoStaticState> {
+  if (typeof value !== "object" || value === null || Array.isArray(value)) {
+    return false;
+  }
+  const candidate = value as MarimoStaticState;
+  if (!isStringToStringRecord(candidate.files)) {
+    return false;
+  }
+  if (
+    candidate.modelNotifications !== undefined &&
+    !Array.isArray(candidate.modelNotifications)
+  ) {
+    return false;
+  }
+  return true;
+}
+
+function getMarimoStaticState(): Readonly<MarimoStaticState> | undefined {
+  const state = window?.__MARIMO_STATIC__;
+  return isMarimoStaticState(state) ? state : undefined;
+}
+
 export function isStaticNotebook(): boolean {
-  return window?.__MARIMO_STATIC__ !== undefined;
+  return getMarimoStaticState() !== undefined;
 }
 
 export function getStaticVirtualFiles(): StaticVirtualFiles {
-  invariant(window.__MARIMO_STATIC__ !== undefined, "Not a static notebook");
-
-  return window.__MARIMO_STATIC__.files;
+  const state = getMarimoStaticState();
+  invariant(state !== undefined, "Not a static notebook");
+  return state.files;
 }
 
 export function getStaticModelNotifications(): ModelLifecycle[] | undefined {
-  return window?.__MARIMO_STATIC__?.modelNotifications;
+  return getMarimoStaticState()?.modelNotifications;
 }

frontend/src/plugins/core/RenderHTML.tsx

@@ -16,6 +16,8 @@ import { CopyClipboardIcon } from "@/components/icons/copy-icon";
 import { QueryParamPreservingLink } from "@/components/ui/query-param-preserving-link";
 import { Tooltip } from "@/components/ui/tooltip";
 import { DocHoverTarget } from "@/core/documentation/DocHoverTarget";
+import { hasTrustedNotebookContext } from "@/core/static/export-context";
+import { Logger } from "@/utils/Logger";
 import { sanitizeHtml, useSanitizeHtml } from "./sanitize";
 
 type ReplacementFn = NonNullable<HTMLReactParserOptions["replace"]>;
@@ -98,8 +100,27 @@ const replaceSrcScripts = (domNode: DOMNode): JSX.Element | undefined => {
     if (!src) {
       return;
     }
-    // Check if script already exists
-    if (!document.querySelector(`script[src="${src}"]`)) {
+    // Only append notebook-authored scripts when the page is a trusted
+    // context (the user has run a cell, the page is a trusted export, or
+    // we're running in read/app mode). In untrusted edit mode before any
+    // user interaction, drop the script and log a warning. Outer
+    // sanitization will normally strip <script> tags already; this is
+    // defense-in-depth for flows that reparse children with
+    // alwaysSanitizeHtml: false (see registerReactComponent.getChildren).
+    if (!hasTrustedNotebookContext()) {
+      Logger.warn(
+        `[RenderHTML] refusing <script src> in untrusted context: ${src}`,
+      );
+      // oxlint-disable-next-line react/jsx-no-useless-fragment
+      return <></>;
+    }
+    // Check if script already exists. Avoid building a CSS selector from
+    // notebook-provided input, which can throw for valid URLs containing
+    // selector-significant characters (e.g. IPv6 hosts with `[`/`]`).
+    const scriptExists = [...document.querySelectorAll("script[src]")].some(
+      (existingScript) => existingScript.getAttribute("src") === src,
+    );
+    if (!scriptExists) {
       const script = document.createElement("script");
       script.src = src;
       document.head.append(script);