diff --git a/electron/main.ts b/electron/main.ts
index 3820786..4c0ca35 100644
--- a/electron/main.ts
+++ b/electron/main.ts
@@ -1,168 +1,267 @@
-import { app, BrowserWindow, ipcMain, safeStorage, Notification, shell, nativeImage } from "electron";
-import { ConvexClient } from "convex/browser";
-import { api } from "../convex/_generated/api";
-import path from "path";
-import fs from "fs";
-
-const CONVEX_URL = process.env.CONVEX_URL ?? "https://next-pika-124.convex.cloud";
-const SESSION_FILE = path.join(app.getPath("userData"), "session.enc");
-
-let mainWindow: BrowserWindow | null = null;
-
-// ── Session token storage (encrypted at rest) ──
-
-function readStoredToken(): string | null {
-  try {
-    if (!fs.existsSync(SESSION_FILE)) return null;
-    const encrypted = fs.readFileSync(SESSION_FILE);
-    if (!safeStorage.isEncryptionAvailable()) return null;
-    return safeStorage.decryptString(encrypted);
-  } catch {
-    return null;
-  }
-}
-
-function storeToken(token: string): void {
-  if (!safeStorage.isEncryptionAvailable()) {
-    throw new Error("Encryption not available");
-  }
-  const encrypted = safeStorage.encryptString(token);
-  fs.writeFileSync(SESSION_FILE, encrypted);
-}
-
-function clearToken(): void {
-  try {
-    fs.unlinkSync(SESSION_FILE);
-  } catch {
-    // file may not exist
-  }
-}
-
-// ── IPC handlers ──
-
-ipcMain.handle("store-session", (_event, token: string) => {
-  storeToken(token);
-  startNotificationSubscription(token);
-});
-
-ipcMain.handle("get-session", () => {
-  return readStoredToken();
-});
-
-ipcMain.handle("clear-session", () => {
-  clearToken();
-  stopNotificationSubscription();
-});
-
-ipcMain.handle("open-external", (_event, url: string) => {
-  shell.openExternal(url);
-});
-
-// ── Native notification bridge ──
-
-let notifClient: ConvexClient | null = null;
-let lastSeenTimestamp = Date.now();
-
-function startNotificationSubscription(sessionToken: string) {
-  stopNotificationSubscription();
-
-  // Set baseline to now so we only fire for truly new notifications
-  lastSeenTimestamp = Date.now();
-  let isFirstUpdate = true;
-
-  notifClient = new ConvexClient(CONVEX_URL);
-  notifClient.onUpdate(
-    api.queries.getUnreadNotifications,
-    { sessionToken },
-    (notifications: Array<{ title: string; body: string; timestamp: number }>) => {
-      if (!notifications) return;
-
-      // Skip the initial snapshot — only fire for subsequent updates
-      if (isFirstUpdate) {
-        isFirstUpdate = false;
-        if (notifications.length > 0) {
-          lastSeenTimestamp = Math.max(...notifications.map((n) => n.timestamp));
-        }
-        return;
-      }
-
-      for (const n of notifications) {
-        if (n.timestamp > lastSeenTimestamp) {
-          const notif = new Notification({ title: n.title, body: n.body ?? "" });
-          notif.show();
-        }
-      }
-      if (notifications.length > 0) {
-        const maxTs = Math.max(...notifications.map((n) => n.timestamp));
-        if (maxTs > lastSeenTimestamp) {
-          lastSeenTimestamp = maxTs;
-        }
-      }
-    },
-  );
-}
-
-function stopNotificationSubscription() {
-  if (notifClient) {
-    notifClient.close();
-    notifClient = null;
-  }
-}
-
-// ── Window creation ──
-
-function createWindow() {
-  mainWindow = new BrowserWindow({
-    width: 1200,
-    height: 800,
-    backgroundColor: "#09090b",
-    titleBarStyle: "hiddenInset",
-    icon: path.join(__dirname, "../../resources/glass-icon.png"),
-    webPreferences: {
-      preload: path.join(__dirname, "../preload/preload.cjs"),
-      contextIsolation: true,
-      nodeIntegration: false,
-      sandbox: false,
-    },
-  });
-
-  if (process.env.ELECTRON_RENDERER_URL) {
-    mainWindow.loadURL(process.env.ELECTRON_RENDERER_URL);
-  } else {
-    mainWindow.loadFile(path.join(__dirname, "../renderer/index.html"));
-  }
-
-
-  mainWindow.on("closed", () => {
-    mainWindow = null;
-  });
-}
-
-app.whenReady().then(() => {
-  if (process.platform === "darwin") {
-    app.dock.setIcon(path.join(__dirname, "../../resources/glass-icon.png"));
-  }
-  createWindow();
-
-  // Start notification subscription if we have a stored session
-  const token = readStoredToken();
-  if (token) {
-    startNotificationSubscription(token);
-  }
-
-  app.on("activate", () => {
-    if (BrowserWindow.getAllWindows().length === 0) {
-      createWindow();
-    }
-  });
-});
-
-app.on("window-all-closed", () => {
-  if (process.platform !== "darwin") {
-    app.quit();
-  }
-});
-
-app.on("before-quit", () => {
-  stopNotificationSubscription();
-});
+import { app, BrowserWindow, ipcMain, safeStorage, Notification, shell } from "electron";
+import { ConvexClient } from "convex/browser";
+import { api } from "../convex/_generated/api";
+import path from "path";
+import fs from "fs";
+
+const CONVEX_URL = process.env.CONVEX_URL ?? "https://next-pika-124.convex.cloud";
+const SESSION_FILE = path.join(app.getPath("userData"), "session.enc");
+
+// Only these two schemes are ever handed to the OS URL handler.
+const ALLOWED_EXTERNAL_PROTOCOLS = new Set(["https:", "http:"]);
+
+// Minimal set of web permissions required for user onboarding clipboard flows
+const ALLOWED_PERMISSIONS = new Set(["clipboard-read", "clipboard-sanitized-write"]);
+
+let mainWindow: BrowserWindow | null = null;
+
+/**
+ * Decides whether a renderer-supplied string may be passed to
+ * `shell.openExternal`.
+ */
+function isSafeExternalUrl(url: unknown): url is string {
+  if (typeof url !== "string" || url.length === 0) return false;
+
+  let parsed: URL;
+  try {
+    parsed = new URL(url);
+  } catch {
+    return false;
+  }
+
+  return ALLOWED_EXTERNAL_PROTOCOLS.has(parsed.protocol);
+}
+
+/**
+ * Opens a URL in the user's browser if it is an allowed scheme,
+ * logging rejections rather than throwing.
+ */
+function openExternalIfSafe(url: unknown): void {
+  if (!isSafeExternalUrl(url)) {
+    console.warn("Refusing to open external URL with a disallowed scheme:", url);
+    return;
+  }
+  void shell.openExternal(url);
+}
+
+/**
+ * Validates whether a navigation target belongs strictly to the application.
+ */
+function isInternalUrl(url: string): boolean {
+  const rendererUrl = process.env.ELECTRON_RENDERER_URL;
+
+  let parsed: URL;
+  try {
+    parsed = new URL(url);
+  } catch {
+    return false;
+  }
+
+  if (rendererUrl) {
+    try {
+      return parsed.origin === new URL(rendererUrl).origin;
+    } catch {
+      return false;
+    }
+  }
+
+  return parsed.protocol === "file:";
+}
+
+// ── Session token storage (encrypted at rest) ──
+
+function readStoredToken(): string | null {
+  try {
+    if (!fs.existsSync(SESSION_FILE)) return null;
+    const encrypted = fs.readFileSync(SESSION_FILE);
+    if (!safeStorage.isEncryptionAvailable()) return null;
+    return safeStorage.decryptString(encrypted);
+  } catch (error) {
+    console.error("Failed to read the stored session token:", error);
+    return null;
+  }
+}
+
+function storeToken(token: string): void {
+  if (!safeStorage.isEncryptionAvailable()) {
+    throw new Error("Encryption not available");
+  }
+  const encrypted = safeStorage.encryptString(token);
+  fs.writeFileSync(SESSION_FILE, encrypted);
+}
+
+function clearToken(): void {
+  try {
+    fs.unlinkSync(SESSION_FILE);
+  } catch {
+    // file may not exist
+  }
+}
+
+// ── IPC handlers ──
+
+ipcMain.handle("store-session", (_event, token: unknown) => {
+  if (typeof token !== "string" || token.length === 0) {
+    throw new Error("store-session expects a non-empty string token");
+  }
+  storeToken(token);
+  startNotificationSubscription(token);
+});
+
+ipcMain.handle("get-session", () => {
+  return readStoredToken();
+});
+
+ipcMain.handle("clear-session", () => {
+  clearToken();
+  stopNotificationSubscription();
+});
+
+ipcMain.handle("open-external", (_event, url: unknown) => {
+  openExternalIfSafe(url);
+});
+
+// ── Native notification bridge ──
+
+let notifClient: ConvexClient | null = null;
+let lastSeenTimestamp = Date.now();
+
+function startNotificationSubscription(sessionToken: string) {
+  stopNotificationSubscription();
+
+  lastSeenTimestamp = Date.now();
+  let isFirstUpdate = true;
+
+  notifClient = new ConvexClient(CONVEX_URL);
+  notifClient.onUpdate(
+    api.queries.getUnreadNotifications,
+    { sessionToken },
+    (notifications: Array<{ title: string; body: string; timestamp: number }>) => {
+      if (!notifications) return;
+
+      if (isFirstUpdate) {
+        isFirstUpdate = false;
+        if (notifications.length > 0) {
+          lastSeenTimestamp = Math.max(...notifications.map((n) => n.timestamp));
+        }
+        return;
+      }
+
+      for (const n of notifications) {
+        if (n.timestamp > lastSeenTimestamp) {
+          const notif = new Notification({ title: n.title, body: n.body ?? "" });
+          notif.show();
+        }
+      }
+      if (notifications.length > 0) {
+        const maxTs = Math.max(...notifications.map((n) => n.timestamp));
+        if (maxTs > lastSeenTimestamp) {
+          lastSeenTimestamp = maxTs;
+        }
+      }
+    },
+  );
+}
+
+function stopNotificationSubscription() {
+  if (notifClient) {
+    notifClient.close();
+    notifClient = null;
+  }
+}
+
+// ── Window creation ──
+
+function createWindow() {
+  mainWindow = new BrowserWindow({
+    width: 1200,
+    height: 800,
+    backgroundColor: "#09090b",
+    titleBarStyle: "hiddenInset",
+    icon: path.join(__dirname, "../../resources/glass-icon.png"),
+    webPreferences: {
+      preload: path.join(__dirname, "../preload/preload.cjs"),
+      contextIsolation: true,
+      nodeIntegration: false,
+      sandbox: true,
+    },
+  });
+
+  mainWindow.webContents.setWindowOpenHandler(({ url }) => {
+    openExternalIfSafe(url);
+    return { action: "deny" };
+  });
+
+  mainWindow.webContents.on("will-navigate", (event, url) => {
+    if (isInternalUrl(url)) return;
+    event.preventDefault();
+    openExternalIfSafe(url);
+  });
+
+  mainWindow.webContents.on("will-redirect", (event, url) => {
+    if (isInternalUrl(url)) return;
+    event.preventDefault();
+    openExternalIfSafe(url);
+  });
+
+  mainWindow.webContents.session.setPermissionRequestHandler((_wc, permission, callback) => {
+    if (ALLOWED_PERMISSIONS.has(permission)) {
+      callback(true);
+      return;
+    }
+    console.warn(`Denied renderer permission request: ${permission}`);
+    callback(false);
+  });
+
+  if (process.env.ELECTRON_RENDERER_URL) {
+    mainWindow.loadURL(process.env.ELECTRON_RENDERER_URL);
+  } else {
+    mainWindow.loadFile(path.join(__dirname, "../renderer/index.html"));
+  }
+
+  mainWindow.on("closed", () => {
+    mainWindow = null;
+  });
+}
+
+// Global protection across all WebContents instances
+app.on("web-contents-created", (_event, contents) => {
+  contents.on("will-attach-webview", (event) => {
+    console.warn("Refused to attach a <webview> tag");
+    event.preventDefault();
+  });
+
+  // Guard window creation on all web contents to prevent unhandled popups
+  contents.setWindowOpenHandler(({ url }) => {
+    openExternalIfSafe(url);
+    return { action: "deny" };
+  });
+});
+
+app.whenReady().then(() => {
+  if (process.platform === "darwin") {
+    app.dock.setIcon(path.join(__dirname, "../../resources/glass-icon.png"));
+  }
+  createWindow();
+
+  const token = readStoredToken();
+  if (token) {
+    startNotificationSubscription(token);
+  }
+
+  app.on("activate", () => {
+    if (BrowserWindow.getAllWindows().length === 0) {
+      createWindow();
+    }
+  });
+});
+
+app.on("window-all-closed", () => {
+  if (process.platform !== "darwin") {
+    app.quit();
+  }
+});
+
+app.on("before-quit", () => {
+  stopNotificationSubscription();
+});
diff --git a/renderer/index.html b/renderer/index.html
index 4d5949c..797ea06 100644
--- a/renderer/index.html
+++ b/renderer/index.html
@@ -1,18 +1,54 @@
-<!doctype html>
-<html lang="en" class="dark">
-  <head>
-    <meta charset="UTF-8" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <title>Vigil</title>
-    <link rel="preconnect" href="https://fonts.googleapis.com" />
-    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
-    <link
-      href="https://fonts.googleapis.com/css2?family=Bricolage+Grotesque:opsz,wght@12..96,500;12..96,600&family=Inter:wght@400;500;600&family=Geist+Mono:wght@400;500&display=swap"
-      rel="stylesheet"
-    />
-  </head>
-  <body class="bg-page text-zinc-50 antialiased">
-    <div id="root"></div>
-    <script type="module" src="./main.tsx"></script>
-  </body>
-</html>
+<!doctype html>
+<html lang="en" class="dark">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <!--
+      Content Security Policy. The renderer previously shipped without one, so a
+      script injected into the page (through remote GitHub/Vercel data rendered by
+      the dashboard, or a compromised bundled dependency) could load further code
+      from any host and exfiltrate to any host. This is delivered as a meta tag
+      rather than a response header because in a packaged build the document is
+      loaded over `file://`, where Electron's `onHeadersReceived` does not apply.
+
+      Notes on the individual directives:
+      - `script-src` keeps `'unsafe-inline'` because Vite injects an inline module
+        preamble for React Refresh in `electron-vite dev`. Removing it requires a
+        nonce-emitting build step, so it is left in rather than silently breaking
+        development; it is the one directive here that is weaker than it should be.
+      - `style-src` needs `'unsafe-inline'` for the styles Tailwind and Radix set
+        on elements at runtime, and the Google Fonts host for the stylesheet
+        linked below.
+      - `connect-src` is scheme-bound rather than host-bound because the Convex
+        deployment is configurable through `VITE_CONVEX_URL`; the `ws://localhost`
+        entry is the dev server's HMR socket.
+      - `object-src`, `frame-src`, `base-uri` and `form-action` are locked down
+        outright: nothing in this app embeds plugins or frames, sets a `<base>`, or
+        submits a form.
+    -->
+    <meta
+      http-equiv="Content-Security-Policy"
+      content="default-src 'self';
+               script-src 'self' 'unsafe-inline';
+               style-src 'self' 'unsafe-inline' https://fonts.googleapis.com;
+               font-src 'self' data: https://fonts.gstatic.com;
+               img-src 'self' data: blob: https:;
+               connect-src 'self' https: wss: ws://localhost:* http://localhost:*;
+               object-src 'none';
+               frame-src 'none';
+               base-uri 'self';
+               form-action 'none';"
+    />
+    <title>Vigil</title>
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
+    <link
+      href="https://fonts.googleapis.com/css2?family=Bricolage+Grotesque:opsz,wght@12..96,500;12..96,600&family=Inter:wght@400;500;600&family=Geist+Mono:wght@400;500&display=swap"
+      rel="stylesheet"
+    />
+  </head>
+  <body class="bg-page text-zinc-50 antialiased">
+    <div id="root"></div>
+    <script type="module" src="./main.tsx"></script>
+  </body>
+</html>