Refuse protocol-relative notification paths and require an observed tap

PUSH-01: appPath now rejects a path that resolves to a leading // after
the URL parser handles dot segments (also %2e), backslashes and stripped
tabs and newlines, and planClick throws if the final URL is off origin.
Regression tests drive openNotification with the attack forms.

PUSH-02: subscribePush no longer asks for notification permission where
navigator.userActivation is unavailable; it throws a typed
PermissionGestureError ('unobservable', or 'inactive' outside a tap).
The test for that path now overrides userActivation directly: the old one
passed undefined into a defaulted parameter and so never exercised it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/push/notification.test.ts

@@ -33,6 +33,21 @@ describe('appPath', () => {
   it('resolves dot segments and keeps the result on origin', () => {
     expect(appPath('/plan/../discover', origin)).toBe('/discover')
   })
+
+  // Each of these starts with a single / but resolves to a path starting with
+  // //, which a browser reads as another host.
+  it.each([
+    '/..//evil.example/path',
+    '/plan/..//evil.example/path',
+    '/..\\\\evil.example/path',
+    '/./\\evil.example',
+    '/.\\/evil.example',
+    '/%2e%2e//evil.example/path',
+    '/.\t.//evil.example/path',
+    '/..\n//evil.example',
+  ])('refuses %j, which resolves to a protocol-relative path', (raw) => {
+    expect(appPath(raw, origin)).toBeNull()
+  })
 })
 
 describe('parsePushPayload', () => {
@@ -120,6 +135,10 @@ describe('clickPath', () => {
 })
 
 describe('planClick', () => {
+  it('refuses a path that resolves off origin', () => {
+    expect(() => planClick([], '//evil.example/path', origin)).toThrow(/resolves off origin/)
+  })
+
   const at = (path: string, focused = false) => ({ url: origin + path, focused })
 
   it('opens a new window when no MealQuest window is open', () => {
@@ -188,4 +207,25 @@ describe('openNotification', () => {
     await openNotification({ url: 'https://evil.example/' }, all, origin)
     expect(all.openWindow).toHaveBeenCalledWith(`${origin}/`)
   })
+
+  it.each(['/..//evil.example/path', '/..\\\\evil.example/path', '/%2e%2e//evil.example/path', '/.\t.//evil.example/path'])(
+    'never leaves origin for %j, which resolves to a protocol-relative path',
+    async (url) => {
+      const win = window('/plan', true)
+      const all = clients([win])
+      await openNotification({ url }, all, origin)
+      expect(win.navigate).toHaveBeenCalledWith(`${origin}/`)
+      expect(all.openWindow).not.toHaveBeenCalled()
+
+      const none = clients([])
+      await openNotification({ url }, none, origin)
+      expect(none.openWindow).toHaveBeenCalledWith(`${origin}/`)
+    },
+  )
+
+  it('still opens an internal path that uses dot segments', async () => {
+    const all = clients([])
+    await openNotification({ url: '/plan/../discover' }, all, origin)
+    expect(all.openWindow).toHaveBeenCalledWith(`${origin}/discover`)
+  })
 })

web/src/push/notification.ts

@@ -31,7 +31,10 @@ function isRecord(value: unknown): value is Record<string, unknown> {
 
 // appPath returns raw as a path on origin (path, query and fragment), or null
 // when raw is not a path-absolute URL that stays on origin. A payload never
-// sends the household to another site.
+// sends the household to another site. The path is checked after the parser
+// has resolved it: dot segments (also as %2e), backslashes and stripped tabs
+// and newlines can all turn an innocent-looking path into one starting with
+// //, which a browser would read as another host.
 export function appPath(raw: string, origin: string): string | null {
   if (!raw.startsWith('/') || raw.startsWith('//')) return null
   let url: URL
@@ -40,7 +43,7 @@ export function appPath(raw: string, origin: string): string | null {
   } catch {
     return null
   }
-  if (url.origin !== origin) return null
+  if (url.origin !== origin || url.pathname.startsWith('//')) return null
   return url.pathname + url.search + url.hash
 }
 
@@ -130,9 +133,14 @@ export type ClickPlan<W> = { action: 'focus'; window: W; url: string; navigate:
 
 // planClick decides a tap on a notification that opens path: the focused
 // MealQuest window if there is one, else the first open one, navigated to
-// path unless it is already there; with none open, a new window.
+// path unless it is already there; with none open, a new window. A path that
+// resolves off origin is an error: a tap never leaves MealQuest.
 export function planClick<W extends AppWindow>(windows: readonly W[], path: string, origin: string): ClickPlan<W> {
-  const url = new URL(path, origin).href
+  const resolved = new URL(path, origin)
+  if (resolved.origin !== origin) {
+    throw new Error(`MealQuest: notification path ${JSON.stringify(path)} resolves off origin to ${resolved.origin}`)
+  }
+  const url = resolved.href
   const ours = windows.filter((w) => URL.canParse(w.url) && new URL(w.url).origin === origin)
   const target = ours.find((w) => w.focused) ?? ours[0]
   if (target === undefined) return { action: 'open', url }

web/src/push/subscribe.test.ts

@@ -5,6 +5,7 @@ import {
   VAPID_PUBLIC_KEY_PATH,
   decodeVapidKey,
   encodeBase64url,
+  PermissionGestureError,
   subscribePush,
   subscriptionBody,
   unsubscribePush,
@@ -36,7 +37,7 @@ function subscription(key: ArrayBuffer | null = vapidKey.buffer, at = endpoint)
 type Setup = {
   permission?: NotificationPermission
   answer?: NotificationPermission
-  active?: boolean | undefined
+  active?: boolean
   current?: BrowserPushSubscription | null
   registered?: boolean
   subscribeError?: unknown
@@ -63,7 +64,7 @@ function setup({
     serviceWorker: { getRegistration: vi.fn(async () => (registered ? { pushManager } : undefined)) },
     pushManager: true,
     notification,
-    userActivation: active === undefined ? undefined : { isActive: active },
+    userActivation: { isActive: active },
     userAgent: 'Mozilla/5.0 Test',
   }
   const calls: { path: string; request?: ApiRequest }[] = []
@@ -155,14 +156,26 @@ describe('subscribePush', () => {
 
   it('refuses to ask for permission outside a tap', async () => {
     const { env, api, notification } = setup({ active: false })
-    await expect(subscribePush(api, env)).rejects.toThrow(/only be asked for from a tap/)
+    const error = await subscribePush(api, env).catch((e: unknown) => e)
+    expect(error).toBeInstanceOf(PermissionGestureError)
+    expect(error).toMatchObject({ reason: 'inactive', message: expect.stringMatching(/only be asked for from a tap/) })
     expect(notification.requestPermission).not.toHaveBeenCalled()
+    expect(api.apiFetch).not.toHaveBeenCalled()
   })
 
-  it('asks where the browser cannot say whether a tap is active', async () => {
-    const { env, api, notification } = setup({ active: undefined })
-    expect(await subscribePush(api, env)).toBe('subscribed')
-    expect(notification.requestPermission).toHaveBeenCalled()
+  it('refuses to ask for permission where the browser cannot say whether a tap is active', async () => {
+    const { env, api, notification } = setup()
+    const error = await subscribePush(api, { ...env, userActivation: undefined }).catch((e: unknown) => e)
+    expect(error).toBeInstanceOf(PermissionGestureError)
+    expect(error).toMatchObject({ reason: 'unobservable', message: expect.stringMatching(/no navigator.userActivation/) })
+    expect(notification.requestPermission).not.toHaveBeenCalled()
+    expect(api.apiFetch).not.toHaveBeenCalled()
+  })
+
+  it('does not need to observe a tap once permission is granted', async () => {
+    const { env, api, notification } = setup({ permission: 'granted' })
+    expect(await subscribePush(api, { ...env, userActivation: undefined })).toBe('subscribed')
+    expect(notification.requestPermission).not.toHaveBeenCalled()
   })
 
   it('does not ask again once permission is granted, even outside a tap', async () => {

web/src/push/subscribe.ts

@@ -58,6 +58,23 @@ export function browserPushEnvironment(): PushEnvironment {
 
 type PushApi = Pick<ApiClient, 'apiFetch'>
 
+// PermissionGestureError is why subscribePush refused to ask for notification
+// permission: no tap is active right now ('inactive'), or the browser cannot
+// say whether one is ('unobservable', no navigator.userActivation).
+export class PermissionGestureError extends Error {
+  readonly reason: 'inactive' | 'unobservable'
+
+  constructor(reason: 'inactive' | 'unobservable') {
+    super(
+      reason === 'inactive'
+        ? 'subscribePush: notification permission can only be asked for from a tap on a button'
+        : 'subscribePush: this browser cannot report whether a tap is active (no navigator.userActivation), so notification permission is not asked for',
+    )
+    this.name = 'PermissionGestureError'
+    this.reason = reason
+  }
+}
+
 // encodeBase64url encodes bytes as unpadded base64url, as the server wants
 // subscription keys.
 export function encodeBase64url(bytes: ArrayBuffer): string {
@@ -133,7 +150,9 @@ function errorName(error: unknown): string | undefined {
 // subscribePush turns on Web Push on this device. Call it only from the
 // household's tap on a button: when the browser has not yet been asked, it
 // asks for notification permission, which browsers allow only during a user
-// gesture, and it refuses to ask outside one. Permission is asked before
+// gesture, and it refuses to ask outside one — or where the browser cannot
+// say whether a gesture is active — with a PermissionGestureError. Permission
+// is asked before
 // anything is awaited so the gesture still counts. With permission, it
 // subscribes the browser with the server's VAPID public key — replacing a
 // subscription made with an older key — and stores the subscription on the
@@ -144,11 +163,8 @@ export async function subscribePush(api: PushApi, env: PushEnvironment): Promise
 
   let permission = notification.permission
   if (permission === 'default') {
-    // Where the browser cannot say whether a gesture is active, it enforces
-    // the rule itself.
-    if (env.userActivation !== undefined && !env.userActivation.isActive) {
-      throw new Error('subscribePush: notification permission can only be asked for from a tap on a button')
-    }
+    if (env.userActivation === undefined) throw new PermissionGestureError('unobservable')
+    if (!env.userActivation.isActive) throw new PermissionGestureError('inactive')
     permission = await notification.requestPermission()
   }
   if (permission === 'denied') return 'denied'