diff --git a/__test__/hostOnlyListeners.test.ts b/__test__/hostOnlyListeners.test.ts
new file mode 100644
index 00000000..563bc30d
--- /dev/null
+++ b/__test__/hostOnlyListeners.test.ts
@@ -0,0 +1,63 @@
+import postRobot from "post-robot";
+
+import Asset from "../src/stack/api/asset";
+import { IAppConfigInitData, LocationType } from "../src/types";
+import UiLocation from "../src/uiLocation";
+
+jest.mock("post-robot");
+
+// MKT-22128: the host (app-extension-component) sends extensionEvent and
+// uploadReady_<uid> from the window that holds the app iframe, i.e.
+// window.parent. A listener without a window filter also accepts the same
+// messages from sibling app frames, so both must be scoped to window.parent.
+describe("host-only post-robot listeners (MKT-22128)", () => {
+    // jsdom's window.parent is window itself; a distinct parent proves the
+    // listener is bound to the parent and not to the app's own window.
+    const fakeParent = {} as Window;
+
+    beforeEach(() => {
+        jest.spyOn(window, "parent", "get").mockReturnValue(fakeParent);
+        (postRobot as any).on.mockReturnValue({ cancel: jest.fn() });
+        (postRobot as any).sendToParent.mockResolvedValue({ data: {} });
+    });
+
+    afterEach(() => {
+        jest.restoreAllMocks();
+        jest.clearAllMocks();
+        window["postRobot"] = undefined;
+    });
+
+    it("listens for extensionEvent from window.parent only", () => {
+        new UiLocation({
+            type: LocationType.APP_CONFIG_WIDGET,
+            app_id: "app_id",
+            installation_uid: "installation_uid",
+            extension_uid: "extension_uid",
+            region: "NA",
+            endpoints: { CMA: "", APP: "", DEVELOPER_HUB: "" },
+            stack: {} as any,
+            user: {} as any,
+            currentBranch: "main",
+            manifest: {} as any,
+        } as IAppConfigInitData);
+
+        const call = (postRobot as any).on.mock.calls.find(
+            ([name]) => name === "extensionEvent"
+        );
+        expect(call).toBeDefined();
+        // compare by identity: printing a Window on failure exhausts memory
+        expect(call[1]?.window === fakeParent).toBe(true);
+        expect(typeof call[2]).toBe("function");
+    });
+
+    it("listens for uploadReady from window.parent only", async () => {
+        await Asset({}).uploadAsset([new Blob(["x"])]);
+
+        const call = (postRobot as any).on.mock.calls.find(([name]) =>
+            String(name).startsWith("uploadReady_")
+        );
+        expect(call).toBeDefined();
+        expect(call[1]?.window === fakeParent).toBe(true);
+        expect(typeof call[2]).toBe("function");
+    });
+});
diff --git a/src/stack/api/asset/index.ts b/src/stack/api/asset/index.ts
index 653b52bf..a0ce4c99 100755
--- a/src/stack/api/asset/index.ts
+++ b/src/stack/api/asset/index.ts
@@ -274,6 +274,7 @@ class Asset extends Base {
             try {
                 const uploadReadyListener = postRobot.on(
                     `uploadReady_${uid}`,
+                    { window: window.parent },
                     function () {
                         window.parent.postMessage(
                             {
diff --git a/src/types/post-robot.d.ts b/src/types/post-robot.d.ts
index 00cbc6df..80770a29 100644
--- a/src/types/post-robot.d.ts
+++ b/src/types/post-robot.d.ts
@@ -23,7 +23,11 @@ declare module "post-robot" {
         cancel: () => void;
     }
 
-    export function on(name: string, handler?: HandlerType): CancelableType;
+    export function on(
+        name: string,
+        options?: ServerOptionsType | HandlerType,
+        handler?: HandlerType
+    ): CancelableType;
 
     export function once(
         name: string,
diff --git a/src/uiLocation.ts b/src/uiLocation.ts
index b84d68f7..bb27d01b 100755
--- a/src/uiLocation.ts
+++ b/src/uiLocation.ts
@@ -348,7 +348,9 @@ class UiLocation {
         }
 
         try {
-            postRobot.on("extensionEvent", async (event) => {
+            // Only the host (the window holding this iframe) sends events; ignore sibling frames.
+            const fromHost = { window: window.parent };
+            postRobot.on("extensionEvent", fromHost, async (event) => {
                 if (event.data.name === "entrySave") {
                     emitter.emitEvent("entrySave", [{ data: event.data.data }]);
                     emitter.emitEvent("updateFields", [