2 files changed, 8 insertions, 3 deletions

diff --git a/ext/bg/js/settings/popup-preview-frame.js b/ext/bg/js/settings/popup-preview-frame.js
index e900d4e2..890b8c96 100644
--- a/ext/bg/js/settings/popup-preview-frame.js
+++ b/ext/bg/js/settings/popup-preview-frame.js
@@ -27,6 +27,7 @@ class SettingsPopupPreview {
         this.popupShown = false;
         this.themeChangeTimeout = null;
         this.textSource = null;
+        this._targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
     }
 
     static create() {
@@ -97,6 +98,8 @@ class SettingsPopupPreview {
     }
 
     onMessage(e) {
+        if (e.origin !== this._targetOrigin) { return; }
+
         const {action, params} = e.data;
         const handler = SettingsPopupPreview._messageHandlers.get(action);
         if (typeof handler !== 'function') { return; }
diff --git a/ext/bg/js/settings/popup-preview.js b/ext/bg/js/settings/popup-preview.js
index 0d20471e..d1d2ff5e 100644
--- a/ext/bg/js/settings/popup-preview.js
+++ b/ext/bg/js/settings/popup-preview.js
@@ -40,20 +40,22 @@ function showAppearancePreview() {
 
     window.wanakana.bind(text[0]);
 
+    const targetOrigin = chrome.runtime.getURL('/').replace(/\/$/, '');
+
     text.on('input', () => {
         const action = 'setText';
         const params = {text: text.val()};
-        frame.contentWindow.postMessage({action, params}, '*');
+        frame.contentWindow.postMessage({action, params}, targetOrigin);
     });
     customCss.on('input', () => {
         const action = 'setCustomCss';
         const params = {css: customCss.val()};
-        frame.contentWindow.postMessage({action, params}, '*');
+        frame.contentWindow.postMessage({action, params}, targetOrigin);
     });
     customOuterCss.on('input', () => {
         const action = 'setCustomOuterCss';
         const params = {css: customOuterCss.val()};
-        frame.contentWindow.postMessage({action, params}, '*');
+        frame.contentWindow.postMessage({action, params}, targetOrigin);
     });
 
     container.append(frame);