diff --git a/assets/js/exelearning-editor.js b/assets/js/exelearning-editor.js
index 0c22a05..acfea0a 100644
--- a/assets/js/exelearning-editor.js
+++ b/assets/js/exelearning-editor.js
@@ -322,7 +322,13 @@
 			const iframeWindow = this.iframe[0]?.contentWindow;
 
 			if ( ! data || ! data.type || ! iframeWindow || event.source !== iframeWindow ) {
-				if ( data?.source === 'wp-exe-editor' && data.type === 'request-save' ) {
+				// The standalone editor page relays Ctrl+S through its own window.
+				if (
+					data?.source === 'wp-exe-editor' &&
+					data.type === 'request-save' &&
+					event.source === window &&
+					event.origin === window.location.origin
+				) {
 					this.requestSave();
 				}
 				return;
diff --git a/assets/js/wp-exe-bridge.js b/assets/js/wp-exe-bridge.js
index 50c107f..1882105 100644
--- a/assets/js/wp-exe-bridge.js
+++ b/assets/js/wp-exe-bridge.js
@@ -273,6 +273,10 @@
 		if ( ! message.type || message.source === 'wp-exe-editor' ) {
 			return;
 		}
+		// Only the embedding WordPress page may drive save/export.
+		if ( event.source !== window.parent || ( '*' !== targetOrigin && event.origin !== targetOrigin ) ) {
+			return;
+		}
 
 		try {
 			switch ( message.type ) {
diff --git a/tests/js/exelearning_editor.test.js b/tests/js/exelearning_editor.test.js
index fccd191..9d69ccc 100644
--- a/tests/js/exelearning_editor.test.js
+++ b/tests/js/exelearning_editor.test.js
@@ -592,6 +592,17 @@ describe( 'exelearning-editor: the conversation with the editor', () => {
 		expect( messagesOfType( posted, 'WP_REQUEST_SAVE' ) ).toHaveLength( 1 );
 	} );
 
+	it( 'ignores a save request relayed from another window or origin', async () => {
+		const editor = await loadEditorOn( MODAL_MARKUP );
+		const posted = stubEditorWindow( editor );
+		const data = { source: 'wp-exe-editor', type: 'request-save' };
+
+		await editor.handleMessage( { data, source: {}, origin: window.location.origin } );
+		await editor.handleMessage( { data, source: window, origin: 'https://evil.test' } );
+
+		expect( messagesOfType( posted, 'WP_REQUEST_SAVE' ) ).toHaveLength( 0 );
+	} );
+
 	it( 'asks the editor for the file when the save button is pressed', async () => {
 		const editor = await loadEditorOn( MODAL_MARKUP );
 		const posted = stubEditorWindow( editor );
diff --git a/tests/js/wp_exe_bridge.test.js b/tests/js/wp_exe_bridge.test.js
index c32babb..fd180e2 100644
--- a/tests/js/wp_exe_bridge.test.js
+++ b/tests/js/wp_exe_bridge.test.js
@@ -135,8 +135,10 @@ async function settle() {
 }
 
 /** Deliver a protocol message from the parent and let the bridge answer it. */
-async function send( data ) {
-	window.dispatchEvent( new window.MessageEvent( 'message', { data } ) );
+async function send( data, from = window.parent, origin = '' ) {
+	const event = new window.MessageEvent( 'message', { data, origin } );
+	Object.defineProperty( event, 'source', { value: from } );
+	window.dispatchEvent( event );
 	await settle();
 }
 
@@ -250,6 +252,33 @@ describe( 'wp-exe-bridge: announcing itself to the parent', () => {
 	} );
 } );
 
+describe( 'wp-exe-bridge: who may drive the protocol', () => {
+	it( 'ignores protocol commands from a window other than the parent', async () => {
+		embedIn( { postMessage: ( message ) => posted.push( message ) } );
+		installEditorWithDocument();
+		await loadBridge();
+		posted.length = 0;
+
+		await send( { type: 'GET_PROJECT_INFO', requestId: 'x' }, window );
+
+		expect( messageOf( 'PROJECT_INFO' ) ).toBeUndefined();
+	} );
+
+	it( 'ignores protocol commands from another origin once the parent origin is known', async () => {
+		embedIn( { postMessage: ( message ) => posted.push( message ) } );
+		window.__EXE_EMBEDDING_CONFIG__ = { parentOrigin: 'https://wp.example' };
+		installEditorWithDocument();
+		await loadBridge();
+		posted.length = 0;
+
+		await send( { type: 'GET_PROJECT_INFO', requestId: 'x' }, window.parent, 'https://evil.test' );
+		expect( messageOf( 'PROJECT_INFO' ) ).toBeUndefined();
+
+		await send( { type: 'GET_PROJECT_INFO', requestId: 'y' }, window.parent, 'https://wp.example' );
+		expect( messageOf( 'PROJECT_INFO' ) ).toBeDefined();
+	} );
+} );
+
 describe( 'wp-exe-bridge: the target origin', () => {
 	it( 'posts to the embedding parent origin when one was configured', async () => {
 		const origins = [];