Google plans to improve cookie controls and protections in upcoming versions of the company's Chrome web browser.
The company revealed plans to change how cookies work fundamentally in the web browser in third-party contexts.
Google Chrome will make use of the SameSite cookie attribute to enforce the new behavior by setting it to lax by default. What this means, essentially, is that the Chrome browser won't send cookies with cross-site requests anymore.
SameSite supports the three values not set, lax and strict, with not set the default on today's Internet. SameSite defines access rights to cookies and it the attribute is not set at all, cookie sending is not limited.
A value of strict on the other hand prevents cookies from being sent to all sites in all cross-browsing contexts. In other words, cookies are only sent if the the requesting site matches the site that is shown in the browser's address bar.
Lax is a compromise between better security and convenience. A Lax value would still block cookies from being sent in third-party contexts, e.g. when requested from a different site, but it would allow cookies to be sent if the user would follow a link to the site.
The "SameSite" attribute limits the scope of the cookie such that it will only be attached to requests if those requests are same-site, as defined by the algorithm in Section 5.2. For example, requests for "https://example.com/sekrit-image" will attach same-site cookies if
and only if initiated from a context whose "site for cookies" is "example.com".
If the "SameSite" attribute's value is "Strict", the cookie will only be sent along with "same-site" requests. If the value is "Lax", the cookie will be sent with same-site requests, and with "cross-site" top-level navigations, as described in Section 126.96.36.199. (via IETF)
Developers and site operators will have to define SameSite values explicitly if they require different values. If they don't, Lax is enforced.
The change has significant consequences. First, it is beneficial for security as it protects cookies from cross-site injections and data disclosure attacks like CSRF (Cross-Site Request Forgery) by default. Google plans to limit cross-site cookies to secure contexts (HTTPS) in the future to improve privacy further.
Google Chrome will feature new cookie controls that "enable users to clear all such cookies" without impacting any "single domain cookies" so that logins and preferences set by single domain cookies are preserved.
Chrome users who run development versions of Chrome may experiment with new SameSite defaults already.
Note that some sites may break when you enable these in Google Chrome. You can undo the changes at any time by setting the experiments to Default or Disabled.
Mozilla introduced SameSite support in Firefox 60.
It is not clear yet when the new controls or regulation is implemented in Chrome Stable. Chrome Canary users can test some of it already. The feature improves protections against CSRF and other attacks significantly.
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