Chrome Adds Device-Bound Credentials to Counter Session Cookie Theft

Google has introduced a Chrome security feature designed to reduce the risk of account takeovers caused by stolen session cookies. Called device-bound session credentials, or DBSCs, the protection links a browser session to a unique encryption key stored within the device running Chrome.

The feature addresses an increasingly important part of account security. Measures such as two-factor authentication and passkeys can strengthen the login process, but session cookies allow users to remain authenticated after that process is complete. Protecting those cookies is therefore critical to protecting active sessions.

Why session cookies matter

Websites use session cookies to make browsing faster and more convenient after a user signs in. A session cookie is a unique string of characters stored by a website in the browser.

Once a user has successfully authenticated, the website’s server sets a session cookie. That cookie effectively confirms that the login has already taken place. The website can then recognize the session as the user moves between pages, rather than requesting credentials every time a new page opens.

This approach is particularly useful on sensitive websites that require authentication. Without session cookies, users could be forced to repeat the credential exchange throughout a browsing session.

The same convenience also makes these cookies valuable to attackers. If a valid session cookie is stolen, the security issue shifts away from the original login method. The account may have been protected by two-factor authentication, a passkey, or another measure, but the session cookie represents a browser session that has already passed those checks.

How device-bound session credentials work

Chrome’s DBSC feature is intended to protect against session cookie theft by creating a unique encryption key for the browser session. Instead of treating the session only as information that can be stored by the browser, the system connects it to a key held on the device.

The central elements are:

Chrome generates a unique encryption key.
The key is stored in a protected, silicon-resident area of the device.
The resulting session credential is bound to that device.

This design focuses on the point after authentication. Two-factor authentication and passkeys help determine whether a person should be allowed to sign in. DBSCs are aimed at preserving the integrity of the session that follows a successful sign-in.

By placing the key in a protected part of the device, Chrome adds a device-specific component to the session. The protection is therefore designed as an antidote to attacks that rely on taking session cookies from one environment and using them to support an account takeover.

Where Chrome stores the key

The protected area used for DBSCs has different names depending on the operating system. On Windows computers, Chrome stores the key in the Trusted Platform Module, commonly abbreviated as TPM. On macOS and iOS devices, the corresponding protected area is called the Secure Enclave. Other platforms use different terminology for their implementations.

These components act as silicon-resident fortresses for the unique encryption key. The key is not merely another browser value stored alongside ordinary session information. Its location within the device is the defining part of the new protection.

Recently released versions of Chrome for Windows and macOS generate a key and store it in the applicable protected area:

Windows: The key is stored in the TPM.
macOS: The key is stored in the Secure Enclave.

Although the underlying names differ across systems, the purpose is consistent: keeping the encryption key within a protected component of the device running the browser.

A safeguard for the post-login stage

DBSCs complement existing authentication protections rather than replacing them. Two-factor authentication, passkeys, and similar technologies are centered on the act of signing in. Session cookies serve a different purpose by allowing the website to remember that authentication has already succeeded.

Chrome’s new feature targets this second stage. Its value lies in adding protection to the credential that sustains an authenticated session as the user navigates a website.

That distinction is important when considering account security as a complete process:

The user authenticates with the website.
The server creates a session cookie confirming the successful login.
The browser uses that cookie as the user opens additional pages.
DBSCs bind the session to a unique key stored in the device’s protected hardware area.

The feature therefore addresses a security gap that can remain even when the initial login uses stronger authentication.

Conclusion

Chrome’s adoption of device-bound session credentials adds a new layer of protection for authenticated browsing sessions. By generating a unique encryption key and storing it in a device’s TPM or Secure Enclave, the browser is designed to make stolen session cookies less useful for account takeovers. The approach reinforces the security of what happens after a user has successfully signed in.

Original source: Ars

Originally reported by Ars.