As this is a proposed new standard, we expect other major browsers to adopt this behavior in future. This means that the cookie is only sent in cross-site requests that meet specific criteria, even though the developers never configured this behavior. If the website issuing the cookie doesn't explicitly set a SameSite attribute, Chrome automatically applies Lax restrictions by default. Set-Cookie: session=0F8tgdOhi9ynR1M9wa3ODa SameSite=StrictĪlthough this offers some protection against CSRF attacks, none of these restrictions provide guaranteed immunity, as we'll demonstrate using deliberately vulnerable, interactive labs later in this section. To do this, they just have to include the SameSite attribute in the Set-Cookie response header, along with their preferred value: As these requests typically require a cookie associated with the victim's authenticated session, the attack will fail if the browser doesn't include this.Īll major browsers currently support the following SameSite restriction levels:ĭevelopers can manually configure a restriction level for each cookie they set, giving them more control over when these cookies are used. This can help to reduce users' exposure to CSRF attacks, which induce the victim's browser to issue a request that triggers a harmful action on the vulnerable website. SameSite works by enabling browsers and website owners to limit which cross-site requests, if any, should include specific cookies. We'll see an example of this in one of the labs later.īefore the SameSite mechanism was introduced, browsers sent cookies in every request to the domain that issued them, even if the request was triggered by an unrelated third-party website. This is an important distinction as it means that any vulnerability enabling arbitrary JavaScript execution can be abused to bypass site-based defenses on other domains belonging to the same site. Crucially, this means that a cross-origin request can still be same-site, but not the other way around. Although note that the port is often inferred from the scheme.Īs you can see from this example, the term "site" is much less specific as it only accounts for the scheme and last part of the domain name. Two URLs are considered to have the same origin if they share the exact same scheme, domain name, and port. Although they're closely related, it's important not to use the terms interchangeably as conflating the two can have serious security implications. The difference between a site and an origin is their scope a site encompasses multiple domain names, whereas an origin only includes one. What's the difference between a site and an origin? This is just a way of accounting for the reserved multipart suffixes that are treated as top-level domains in practice, such as. You may come across the term "effective top-level domain" (eTLD). This means that a link from to is treated as cross-site by most browsers. When determining whether a request is same-site or not, the URL scheme is also taken into consideration. net, plus one additional level of the domain name. In the context of SameSite cookie restrictions, a site is defined as the top-level domain (TLD), usually something like. What is a site in the context of SameSite cookies? We'll then look at some of the most common ways you may be able to bypass these restrictions, enabling CSRF and other cross-site attacks on websites that may initially appear secure. In this section, we'll first cover how the SameSite mechanism works and clarify some of the related terminology. As a result, it's essential to have solid grasp of how these restrictions work, as well as how they can potentially be bypassed, in order to thoroughly test for cross-site attack vectors. This is a proposed standard, and we expect other major browsers to adopt this behavior in the future. Since 2021, Chrome applies Lax SameSite restrictions by default if the website that issues the cookie doesn't explicitly set its own restriction level. SameSite cookie restrictions provide partial protection against a variety of cross-site attacks, including CSRF, cross-site leaks, and some CORS exploits. SameSite is a browser security mechanism that determines when a website's cookies are included in requests originating from other websites. Be wary of cross-origin, same-site attacks.Validation of Referer can be circumvented.Validation of Referer depends on header being present. Bypassing Lax restrictions with newly issued cookies.Bypassing restrictions via vulnerable sibling domains.Bypassing restrictions using on-site gadgets.Bypassing Lax restrictions using GET requests.Validation depends on token being present.
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