fix(hub): require the passphrase to change the e-mail on file

A member hands its hub access token to every node it connects to (the MNP
handshake), so a node operator holds a live bearer token for that member.
PATCH /v1/users/me {email} needed only that token, and the confirmation code
goes to the new address — so an operator could point the account's e-mail at
their own inbox, confirm it, and then use the passphrase-reset path to take the
account over. This is the immediate mitigation of that chain; the full fix
(a node-audience token distinct from the API session token) follows.

Changing the address now requires the passphrase-derived auth_key, verified
through the same throttle as a passphrase change or an account deletion — the
hub still never sees the passphrase. A PATCH that does not change the address is
unaffected. The profile page prompts for the passphrase and derives auth_key
with the existing MeshBayKeys.deriveAuthKey, as the delete and change-password
flows already do.

test_email_change_requires_passphrase.py: refused without / with a wrong
passphrase, proceeds with the right one, and a no-email PATCH still works; red
before, green after. test_mail_is_not_a_relay.py updated to pass the auth_key.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

2 files changed, 46 insertions, 6 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/users.py b/packages/meshbay-hub/src/meshbay_hub/api/users.py
index a994acb..7046c2f 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/users.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/users.py
@@ -728,6 +728,14 @@ async def get_current_user_info(
 
 class UpdateProfileRequest(BaseModel):
     email: str | None = None
+    # Required to change the address on file. Changing it is the first step of
+    # an account takeover from a bare access token: the confirmation code goes
+    # to the new (attacker) address, and a verified address then unlocks the
+    # passphrase-reset path. A live access token is not enough for that — the
+    # passphrase is, exactly as for `change_password` and `delete_own_account`.
+    # This matters because a member hands its access token to every node it
+    # connects to (the MNP handshake), so a node operator holds one.
+    auth_key: str | None = None
 
     @field_validator("email")
     @classmethod
@@ -768,6 +776,22 @@ async def update_profile(
         new_email = body.email.strip()
         eh = hash_email_blind(new_email)
 
+        # Changing the address on file requires the passphrase, not merely a
+        # live token. Same second factor, and the same throttle, as a passphrase
+        # change or an account deletion — the hub still never sees the
+        # passphrase, only the derived auth_key.
+        if not body.auth_key:
+            raise HTTPException(
+                status_code=403,
+                detail="Changing your e-mail requires your passphrase.")
+        await _take_login_attempt(db, current_user.username)
+        if not await verify_password_off_loop(
+                body.auth_key, current_user.pw_hash, current_user.pw_salt,
+                current_user.pw_version):
+            raise HTTPException(status_code=403,
+                                detail="Passphrase does not match")
+        await login_throttle.clear(db, current_user.username)
+
         # How often one account may point the hub at a *different* address.
         # Long, because this is the only path where a signed-in account chooses
         # who receives a message, and a short delay alone still allows one
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js b/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
index ed7a2fa..d3d06d7 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/profile-page.js
@@ -37,6 +37,10 @@ export function ProfilePage({ user, onLogout }) {
   const [emailVerifyPending, setEmailVerifyPending] = useState(false);
   const [emailCode, setEmailCode] = useState('');
   const [emailVerifying, setEmailVerifying] = useState(false);
+  // Changing the address on file now needs the passphrase (the hub verifies the
+  // derived auth_key): a bare access token — which every node this account
+  // connects to is handed — must not be able to start an account takeover.
+  const [emailPass, setEmailPass] = useState('');
   const [pinCount, setPinCount] = useState(
     () => (window.MeshBayTransport?.pinnedNodeCount?.() ?? 0));
   const [delOpen, setDelOpen] = useState(false);
@@ -232,12 +236,18 @@ export function ProfilePage({ user, onLogout }) {
   const saveEmail = useCallback(async () => {
     const val = emailDraft.trim();
     if (!val || val === email) { setEmailEditing(false); return; }
+    if (!emailPass) return;   // the Save button is disabled until it is entered
     setEmailSaving(true);
     setEmailStatus('');
     try {
+      // The passphrase is the second factor here, exactly as for a passphrase
+      // change or an account deletion: the hub gets the derived auth_key, never
+      // the passphrase itself.
+      const authKey = await window.MeshBayKeys.deriveAuthKey(emailPass, user.username);
       const resp = await hubFetch('/v1/users/me', {
-        method: 'PATCH', token: user.token, body: { email: val },
+        method: 'PATCH', token: user.token, body: { email: val, auth_key: authKey },
       });
+      setEmailPass('');
       if (resp.email_verification_required) {
         setEmailVerifyPending(true);
         setEmailStatus(t('settings.email_code_sent'));
@@ -248,11 +258,13 @@ export function ProfilePage({ user, onLogout }) {
         setTimeout(() => setEmailStatus(''), 3000);
       }
     } catch (e) {
-      setEmailStatus(e.message);
+      const msg = /403|does not match/i.test(e.message)
+        ? t('settings.pw_wrong_current') : e.message;
+      setEmailStatus(msg);
     } finally {
       setEmailSaving(false);
     }
-  }, [emailDraft, email, user.token]);
+  }, [emailDraft, email, emailPass, user.token, user.username]);
 
   const verifyEmailChange = useCallback(async () => {
     if (!emailCode.trim()) return;
@@ -311,14 +323,18 @@ export function ProfilePage({ user, onLogout }) {
             ? html`<span style="display:flex;gap:8px;align-items:center;flex-wrap:wrap">
                 <input type="email" value=${emailDraft}
                   onInput=${e => setEmailDraft(e.target.value)}
-                  onKeyDown=${e => e.key === 'Enter' && saveEmail()}
                   disabled=${emailVerifyPending}
                   style="font-size:0.9em;padding:4px 8px;border:1px solid var(--border);border-radius:4px" />
                 ${!emailVerifyPending && html`
+                  <input type="password" autocomplete="current-password"
+                    placeholder=${t('login.password')}
+                    value=${emailPass} onInput=${e => setEmailPass(e.target.value)}
+                    onKeyDown=${e => e.key === 'Enter' && saveEmail()}
+                    style="font-size:0.9em;padding:4px 8px;border:1px solid var(--border);border-radius:4px" />
                   <button class="admin-btn" onClick=${saveEmail}
-                    disabled=${emailSaving}>${t('settings.email_save')}</button>
+                    disabled=${emailSaving || !emailPass}>${t('settings.email_save')}</button>
                   <button class="btn-secondary" onClick=${() => {
-                    setEmailEditing(false); setEmailDraft(email);
+                    setEmailEditing(false); setEmailDraft(email); setEmailPass('');
                   }}>${t('settings.cancel')}</button>
                 `}
               </span>`