'Rakuten Ichiba App' for Android 12.4.0 and earlier and 'Rakuten Ichiba App' for iOS 11.7.0 and earlier are vulnerable to improper authorization in handler for custom URL scheme. An arbitrary site may be displayed on the WebView of the product via Intent from another application installed on the user's device. As a result, the user may be redirected to an unauthorized site, and the user may become a victim of a phishing attack.