Verify that blob urls are blob: or data: scheme before fetching

packages/visual-editor/src/data/common.ts

@@ -119,6 +119,9 @@ export const asBlob = async (
   let url: string;
   if (isStoredData(part)) {
     url = part.storedData.handle;
+    if (!url.startsWith("blob:") && !url.startsWith("data:")) {
+      throw new Error("Invalid stored data URL");
+    }
   } else if (isChunk(part)) {
     const { mimetype } = part;
     let { data } = part;

packages/visual-editor/tests/data/as-blob.test.ts

@@ -0,0 +1,141 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { describe, it, mock, beforeEach, afterEach } from "node:test";
+import assert from "node:assert/strict";
+import { asBlob } from "../../src/data/common.js";
+
+describe("asBlob", () => {
+  beforeEach(() => {
+    mock.restoreAll();
+  });
+
+  afterEach(() => {
+    mock.restoreAll();
+  });
+
+  it("rejects a relative URL handle", async () => {
+    const fakeFetch = mock.fn(async () => new Response("data"));
+    mock.method(globalThis, "fetch", fakeFetch);
+
+    const part = {
+      storedData: {
+        handle: "/path/to/resource",
+        mimeType: "application/json",
+      },
+    };
+
+    await assert.rejects(
+      () => asBlob(part),
+      (error: Error) => {
+        assert.ok(
+          error.message.length > 0,
+          "Expected a validation error message"
+        );
+        return true;
+      },
+      "asBlob should reject storedData handles that are relative URLs"
+    );
+
+    assert.equal(
+      fakeFetch.mock.callCount(),
+      0,
+      "fetch must not be called for a relative URL handle"
+    );
+  });
+
+  it("rejects an https: URL handle", async () => {
+    const fakeFetch = mock.fn(async () => new Response("data"));
+    mock.method(globalThis, "fetch", fakeFetch);
+
+    const part = {
+      storedData: {
+        handle: "https://example.com/data",
+        mimeType: "application/json",
+      },
+    };
+
+    await assert.rejects(
+      () => asBlob(part),
+      (error: Error) => {
+        assert.ok(
+          error.message.length > 0,
+          "Expected a validation error message"
+        );
+        return true;
+      },
+      "asBlob should reject storedData handles with https: scheme"
+    );
+
+    assert.equal(
+      fakeFetch.mock.callCount(),
+      0,
+      "fetch must not be called for an https: storedData handle"
+    );
+  });
+
+  it("rejects an http: URL handle", async () => {
+    const fakeFetch = mock.fn(async () => new Response("data"));
+    mock.method(globalThis, "fetch", fakeFetch);
+
+    const part = {
+      storedData: {
+        handle: "http://example.com/data",
+        mimeType: "application/json",
+      },
+    };
+
+    await assert.rejects(
+      () => asBlob(part),
+      (error: Error) => {
+        assert.ok(
+          error.message.length > 0,
+          "Expected a validation error message"
+        );
+        return true;
+      },
+      "asBlob should reject storedData handles with http: scheme"
+    );
+
+    assert.equal(
+      fakeFetch.mock.callCount(),
+      0,
+      "fetch must not be called for an http: storedData handle"
+    );
+  });
+
+  it("fetches a valid blob: URL handle", async () => {
+    const fakeFetch = mock.fn(async () => new Response("blob-data"));
+    mock.method(globalThis, "fetch", fakeFetch);
+
+    const part = {
+      storedData: {
+        handle: "blob:http://localhost/1234-5678",
+        mimeType: "image/png",
+      },
+    };
+
+    const blob = await asBlob(part);
+    assert.ok(blob);
+    assert.equal(fakeFetch.mock.callCount(), 1);
+  });
+
+  it("fetches a valid data: URL handle", async () => {
+    const fakeFetch = mock.fn(async () => new Response("data-content"));
+    mock.method(globalThis, "fetch", fakeFetch);
+
+    const part = {
+      storedData: {
+        handle: "data:text/plain;base64,SGVsbG8=",
+        mimeType: "text/plain",
+      },
+    };
+
+    const blob = await asBlob(part);
+    assert.ok(blob);
+    assert.equal(fakeFetch.mock.callCount(), 1);
+  });
+});