Duolingo

Below the B minimum (70/100) in our RFP clause. A buyer using it would ask for a dated fix for each missing header.

With these headers missing, duolingo.com is more exposed to man-in-the-middle attacks, malicious JavaScript, redirected forms, hijacked payments and clickjacking.

Missing 7

• Content-Security-Policy 0 of 25

  Tells the browser which scripts may run on the page, where its forms may submit, and where it may send data.

  Without it: This is the main defence against malicious JavaScript. If an attacker gets any script onto the page (through a bug, a compromised analytics tag, chat widget or ad, or a poisoned package), the browser runs it with the signed-in user's full access. It can capture what they type, quietly point a sign-in or checkout form at the attacker's server, and skim card numbers as they are entered. A strict policy blocks scripts it does not list, and its form-action and connect-src rules leave stolen data nowhere to go.

• Strict-Transport-Security 0 of 20

  Tells browsers to use HTTPS for this domain, every time, without trying plain HTTP first.

  Without it: The site is open to man-in-the-middle attacks. The first request a user makes (typing the domain, following an old http:// link) can go out unencrypted, and anyone on the same network, such as café, hotel or airport Wi-Fi, can intercept it before the redirect to HTTPS. From there they can read passwords, session cookies and card numbers, serve a fake sign-in page, or inject their own JavaScript into the real one.

• X-Content-Type-Options 0 of 10

  Stops the browser guessing a file's type instead of trusting the type the server declared.

  Without it: A file uploaded as an image or plain text can be reinterpreted as HTML or script and run inside the product's own origin: malicious JavaScript delivered through a harmless-looking upload feature.

• Referrer-Policy 0 of 10

  Limits how much of the current URL is passed to other sites when a user follows a link or the page loads a third-party resource.

  Without it: Full URLs, including paths and query strings that can carry document IDs, search terms, customer names or reset tokens, can leak to every outside script, image host and outbound link. Recent browsers default to a safer policy; older ones and embedded webviews do not.

• Permissions-Policy 0 of 10

  Switches off browser features the product does not use, such as camera, microphone, location and payments, for the page and anything embedded in it.

  Without it: Any script or iframe on the page, including third-party ads and chat widgets, can ask the user for camera, microphone or location access under the vendor's name.

• Cross-Origin-Opener-Policy 0 of 5

  Cuts the link between the product's window and windows opened by, or opening, other sites.

  Without it: A page that opens the product keeps a handle on its window and can later redirect it to a look-alike sign-in or payment page (tab-nabbing) while the user thinks they are still on the real site. It is also part of the isolation browsers need to defend against Spectre-style attacks.

• Cross-Origin-Resource-Policy 0 of 5

  Tells browsers which sites may load this site's resources.

  Without it: Other sites can pull the product's responses into their own pages, which makes side-channel leaks of what a signed-in user can see easier.

Sent 2

• Frame protection 10 of 10

  SAMEORIGIN

• No version disclosure 5 of 5

  server: duo-api

Checked 2026-10-09 at https://www.duolingo.com/. Re-checked every 7 days. The grade covers the headers this website sends, not the product’s overall security. How the grade works.