diff --git a/bundled-addons/aegis/wallet-inject.js b/bundled-addons/aegis/wallet-inject.js
index 1a73782d..fbd8be1d 100644
--- a/bundled-addons/aegis/wallet-inject.js
+++ b/bundled-addons/aegis/wallet-inject.js
@@ -191,13 +191,20 @@ theseus.contextBridge.exposeInMainWorld("wizardconnect", wizardconnect);
 // to us via `window.postMessage` on a namespaced envelope. This mirrors how
 // MetaMask and Phantom bridge extension code back to page code.
 
-// Namespace used on the postMessage envelope. Includes the addon id so a
-// page that runs multiple dapp-wallet extensions doesn't misroute messages.
-const AEGIS_TAG = "aegis-" + theseus.id;
+// Namespace used on the postMessage envelope. Includes the addon id plus a
+// per-page-load nonce: only the main-world bridge we install below knows
+// it, so a cross-origin iframe on the page cannot address the relay. The
+// listener additionally requires the event to come from this very window
+// (e.source === window) — an iframe's postMessage to its parent has
+// e.source === that iframe — so a request can never be attributed to the
+// top-level origin by anything but the top-level page's own scripts. The
+// old fixed tag let any embedded ad frame call the wallet as the page.
+const AEGIS_TAG = "aegis-" + theseus.id + "-" + Array.from(crypto.getRandomValues(new Uint8Array(12)), (b) => b.toString(16).padStart(2, "0")).join("");
 const pendingCalls = new Map();
 window.addEventListener("message", async (e) => {
-  const d = e && e.data;
-  if (!d || d.aegisTag !== AEGIS_TAG) return;
+  if (!e || e.source !== window || e.origin !== location.origin) return;
+  const d = e.data;
+  if (!d || typeof d !== "object" || d.aegisTag !== AEGIS_TAG) return;
   if (d.kind === "request") {
     // Forward main-world → isolated-world → addon.
     try {
@@ -229,8 +236,9 @@ const mainWorldSource = `(function () {
     });
   }
   window.addEventListener("message", (e) => {
-    const d = e && e.data;
-    if (!d || d.aegisTag !== TAG) return;
+    if (!e || e.source !== window) return;
+    const d = e.data;
+    if (!d || typeof d !== "object" || d.aegisTag !== TAG) return;
     if (d.kind === "response") {
       const p = pending.get(d.id);
       if (!p) return;