Google - Better protection against Man in the Middle phishing attacks

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We’re constantly working to improve our phishing protections to keep your information secure. Last year, we announced that we would require JavaScript to be enabled in your browser when you sign in so that we can run a risk assessment whenever credentials are entered on a sign-in page and block the sign-in if we suspect an attack. This is yet another layer of protection on top of existing safeguards like Safe Browsing warnings, Gmail spam filters, and account sign-in challenges.

However, one form of phishing, known as “man in the middle” (MITM), is hard to detect when an embedded browser framework (e.g., Chromium Embedded Framework - CEF) or another automation platform is being used for authentication. MITM intercepts the communications between a user and Google in real-time to gather the user’s credentials (including the second factor in some cases) and sign in. Because we can’t differentiate between a legitimate sign in and a MITM attack on these platforms, we will be blocking sign-ins from embedded browser frameworks starting in June. This is similar to the restriction on webview sign-ins announced in April 2016.

What developers need to know

The solution for developers currently using CEF for authentication is the same: browser-based OAuth authentication. Aside from being secure, it also enables users to see the full URL of the page where they are entering their credentials, reinforcing good anti-phishing practices. If you are a developer with an app that requires access to Google Account data, switch to using browser-based OAuth authentication today.

Source: Google Online Security Blog: Better protection against Man in the Middle phishing attacks