Keep browser evaluation working on strict-policy pages without shadowing page globals (#8973)

* fix(desktop): run browser_evaluate on pages whose CSP omits 'unsafe-eval' * test(desktop): browser_evaluate on pages that allow and forbid eval * test(desktop): e2e opens a page under a CSP without 'unsafe-eval' and evaluates on it * fix(desktop): preserve page globals in browser evaluation Define the supplied function outside every wrapper binding so strict-policy evaluation keeps the original page scope. Co-authored-by: Abdulhakeem Mustapha <abdulhakeemmustapha@gmail.com> --------- Co-authored-by: Abdulhakeem Mustapha <abdulhakeemmustapha@gmail.com> Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>
2026-11-07 08:54:42 +00:00 · 2026-11-07 06:03:12 +00:00
parent daf26892d3
commit 751dc82e6c
3 changed files with 202 additions and 4 deletions
@@ -213,8 +213,18 @@ async function settleDesktopStartup(page) {
  }
 }

+const CSP_PAGE_PATH = "/csp-no-eval";
+
 async function startTargetPage() {
-  const server = createServer((_request, response) => {
+  const server = createServer((request, response) => {
+    if (request.url === CSP_PAGE_PATH) {
+      response.writeHead(200, {
+        "content-type": "text/html; charset=utf-8",
+        "content-security-policy": "default-src 'self'; script-src 'self'",
+      });
+      response.end("<!doctype html><title>CSP page</title><h1>CSP page heading</h1>");
+      return;
+    }
    response.writeHead(200, { "content-type": "text/html; charset=utf-8" });
    response.end(`<!doctype html>
      <html>
@@ -351,6 +361,42 @@ async function waitForGuestActiveElement(client, browserId, elementId) {
  return false;
 }

+// A page whose Content Security Policy omits 'unsafe-eval' refuses eval(); the tools must still work.
+async function verifyEvaluateOnPageWithoutUnsafeEval(client, targetUrl) {
+  const created = await callBrowserTool(client, "browser_new_tab", {
+    url: new URL(CSP_PAGE_PATH, targetUrl).href,
+  });
+  const browserId = created.browserId;
+  assert(typeof browserId === "string", "browser_new_tab returned no browserId for the CSP page");
+  try {
+    await callBrowserTool(client, "browser_wait", {
+      browserId,
+      text: "CSP page heading",
+      timeoutMs: 15_000,
+    });
+    const title = await callBrowserTool(client, "browser_evaluate", {
+      browserId,
+      function: "() => document.title",
+    });
+    assert(
+      JSON.parse(title.resultJson) === "CSP page",
+      `browser_evaluate on a page without 'unsafe-eval' returned ${title.resultJson}`,
+    );
+    // The control: the page itself really does refuse eval().
+    const probe = await callBrowserTool(client, "browser_evaluate", {
+      browserId,
+      function:
+        '() => { try { (0, eval)("1"); return "eval allowed"; } catch (error) { return error.message; } }',
+    });
+    assert(
+      /Content Security Policy/.test(JSON.parse(probe.resultJson)),
+      `The CSP page did not refuse eval(): ${probe.resultJson}`,
+    );
+  } finally {
+    await callBrowserTool(client, "browser_close_tab", { browserId });
+  }
+}
+
 async function createCallerAgent(daemonPort, workspaceId = workspaceIds[0]) {
  const transport = new StreamableHTTPClientTransport(
    new URL(`http://127.0.0.1:${daemonPort}/mcp/agents`),
@@ -736,6 +782,8 @@ async function runRegression({
    document.body.appendChild(overlayRoot);
  });

+  await verifyEvaluateOnPageWithoutUnsafeEval(client, targetUrl);
+
  const created = await callBrowserTool(client, "browser_new_tab", { url: targetUrl });
  const browserId = created.browserId;
  assert(typeof browserId === "string", "browser_new_tab returned no browserId");
@@ -1168,6 +1216,7 @@ async function runRegression({
    snapshot: "passed",
    click: "passed",
    localPageSelectors: "passed",
+    evaluateWithoutUnsafeEval: "passed",
  };
 }

@@ -455,6 +455,34 @@ function browserWithTimingEntries(entries: { resource: unknown[]; navigation: un
  return browser;
 }

+/**
+ * Runs the script the host injects into a page the way Chromium runs it on a page whose Content
+ * Security Policy omits 'unsafe-eval': injected code runs, but code in the page cannot turn a
+ * string into code (eval, new Function). Node's vm refuses string code generation the same way.
+ */
+function pageRunningInjectedScripts(input: {
+  allowEval: boolean;
+  globals?: Record<string, unknown>;
+}) {
+  const page = createContext(
+    { document: { title: "Fixture" }, ...input.globals },
+    { codeGeneration: { strings: input.allowEval, wasm: input.allowEval } },
+  );
+  return (script: string): unknown => runInContext(script, page);
+}
+
+/** A browser whose tab runs the evaluate script in `page`; its other scripts keep the fake answers. */
+function browserEvaluatingIn(page: (script: string) => unknown) {
+  const browser = new BrowserAutomationHarness();
+  const fakeAnswer = browser.tab.executeJavaScript.bind(browser.tab);
+  browser.tab.executeJavaScript = async (script: string) => {
+    if (!script.includes("__PASEO_BROWSER_EVALUATE__")) return fakeAnswer(script);
+    browser.tab.scripts.push(script);
+    return page(script);
+  };
+  return browser;
+}
+
 function requireSnapshotRefs(result: Awaited<ReturnType<BrowserAutomationHarness["snapshot"]>>) {
  expect(result).toEqual({
    requestId: "req-snapshot",
@@ -1645,6 +1673,99 @@ describe("executeAutomationCommand", () => {
    expect(containsScript(browser.tab, "resultJson.slice(0, 79000)")).toBe(true);
  });

+  describe.each([
+    { page: "allows eval", allowEval: true },
+    { page: "forbids eval (its Content Security Policy omits 'unsafe-eval')", allowEval: false },
+  ])("evaluate on a page that $page", ({ allowEval }) => {
+    const evaluate = (browser: BrowserAutomationHarness, source: string) =>
+      browser.execute({
+        command: "evaluate",
+        args: { browserId: BROWSER_A, function: source },
+      });
+
+    test("runs the function and returns its result as JSON", async () => {
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval }));
+
+      expect(await evaluate(browser, "() => document.title")).toEqual({
+        requestId: "req-evaluate",
+        ok: true,
+        result: {
+          command: "evaluate",
+          browserId: BROWSER_A,
+          resultJson: '"Fixture"',
+          truncated: false,
+        },
+      });
+    });
+
+    test("awaits an async function", async () => {
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval }));
+
+      const result = await evaluate(
+        browser,
+        "async () => { await Promise.resolve(); return 6 * 7; }",
+      );
+
+      expect(result).toMatchObject({ ok: true, result: { resultJson: "42" } });
+    });
+
+    test("resolves names against the page's globals, never the wrapper's own", async () => {
+      const globals = {
+        element: "page element",
+        args: "page args",
+        value: "page value",
+        resultJson: "page json",
+        userFunction: "page function",
+        __paseoEvaluate: "page wrapper",
+        readFunction: "page reader",
+      };
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval, globals }));
+
+      const result = await evaluate(
+        browser,
+        "() => [element, args, value, resultJson, userFunction, __paseoEvaluate, readFunction]",
+      );
+
+      expect(result).toMatchObject({
+        ok: true,
+        result: { resultJson: JSON.stringify(Object.values(globals)) },
+      });
+    });
+
+    test("reports what the function throws", async () => {
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval }));
+
+      expect(await evaluate(browser, "() => { throw new Error('boom'); }")).toMatchObject({
+        ok: false,
+        error: { code: "browser_unknown_error", message: "boom" },
+      });
+    });
+
+    test("reports an expression that is not a function", async () => {
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval }));
+
+      expect(await evaluate(browser, "document.title")).toMatchObject({
+        ok: false,
+        error: {
+          code: "browser_unknown_error",
+          message: "browser_evaluate input must evaluate to a function.",
+        },
+      });
+    });
+
+    test("reports a syntax error with the compiler's own message, without touching the page", async () => {
+      const browser = browserEvaluatingIn(pageRunningInjectedScripts({ allowEval }));
+
+      const result = await evaluate(browser, "() => {");
+
+      expect(result).toMatchObject({
+        ok: false,
+        error: { code: "browser_unknown_error", message: expect.stringMatching(/^Unexpected /) },
+      });
+      expect(containsScript(browser.tab, "__PASEO_BROWSER_EVALUATE__")).toBe(false);
+    });
+  });
+
  test("screenshot captures the painted viewport", async () => {
    const browser = new BrowserAutomationHarness();

@@ -1,4 +1,5 @@
 import { isAbsolute, relative, resolve as resolvePath } from "node:path";
+import { Script } from "node:vm";

 import type {
  BrowserAutomationCommand,
@@ -849,6 +850,11 @@ async function executeEvaluate(
      elementExpression = expression;
    }

+    const syntaxError = functionSyntaxError(functionSource);
+    if (syntaxError !== null) {
+      return fail(requestId, "browser_unknown_error", capEvaluateErrorMessage(syntaxError));
+    }
+
    let rawResult: unknown;
    try {
      rawResult = await target.contents.executeJavaScript(
@@ -1550,14 +1556,36 @@ function capEvaluateErrorMessage(message: string): string {
    : message.slice(0, MAX_EVALUATE_ERROR_MESSAGE_LENGTH);
 }

+/**
+ * The syntax error in the agent's function, or null. It is compiled here because a script that
+ * fails to compile in the page only reports "Script failed to execute", and a typo deserves the
+ * compiler's own message. Compiling runs nothing.
+ */
+function functionSyntaxError(functionSource: string): string | null {
+  try {
+    void new Script(`(${functionSource})`);
+    return null;
+  } catch (error) {
+    return error instanceof Error ? error.message : String(error);
+  }
+}
+
+/**
+ * The page script that runs the agent's function and returns its result as bounded JSON.
+ *
+ * The function goes into the script as code, not as a string for the page to eval(): a page whose
+ * Content Security Policy omits 'unsafe-eval' refuses eval() but still runs what the host injects.
+ * The function-producing thunk is an argument defined outside the wrapper, so its names resolve
+ * against the page's globals without capturing any wrapper parameters or locals.
+ */
 function buildEvaluateScript(
  functionSource: string,
  elementExpression: string | undefined,
 ): string {
-  return String.raw`(async () => {
+  return String.raw`(async (readFunction) => {
    const __PASEO_BROWSER_EVALUATE__ = true;
    try {
-      const userFunction = (0, eval)(${JSON.stringify(`(${functionSource})`)});
+      const userFunction = readFunction();
      if (typeof userFunction !== 'function') {
        throw new Error('browser_evaluate input must evaluate to a function.');
      }
@@ -1582,7 +1610,7 @@ function buildEvaluateScript(
 	    } catch (error) {
 	      return { error: error instanceof Error ? error.message : String(error) };
 	    }
-	  })()`;
+	  })(() => (${functionSource}))`;
 }

 async function focusKeypressTarget(