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Comment by jeremyscanvic | Hacker News Reader

Erratum: What I'm saying here only applies for cookies with the attribute SameSite=None so it's irrelevant here, see the comments below.

(Former CTF hobbyist here) You might be mixing up XSS and CSRF protections. Cookie protections are useful against XSS vulnerabilities because they make it harder for attackers to get a hold on user sessions (often mediated through cookies). It doesn't really help against CSRF attacks though. Say you visit attacker.com and it contains an auto-submitting form making a POST request to yourwebsite.com/delete-my-account. In that case, your cookies would be sent along and if no CSRF protection is there (origin checks, tokens, ...) your account might end up deleted. I know it doesn't answer the original question but hope it's useful information nonetheless!

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The SameSite cookie flag is effective against CSRF when you put it on your session cookie, it's one of its main use cases. See https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/... for more information.

SameSite=Lax (default for legacy sites in Chrome) will protect you against POST-based CSRF.

SameSite=Strict will also protect against GET-based CSRF (which shouldn't really exist as GET is not a safe method that should be allowed to trigger state changes, but in practice some applications do it). It does, however, also make it so users clicking a link to your page might not be logged in once they arrive unless you implement other measures.

In practice, SameSite=Lax is appropriate and just works for most sites. A notable exception are POST-based SAML SSO flows, which might require a SameSite=None cookie just for the login flow.

This page has some more information about the drawbacks/weaknesses of SameSite, worth a read: https://developer.mozilla.org/en-US/docs/Web/Security/Attack...

You usually need another method as well

Yes, you're definitely right that there are edge cases and I was simplifying a bit. Notably, it's called SameSite, NOT SameOrigin. Depending on your application that might matter a lot.

In practice, SameSite=Lax is already very effective in preventing _most_ CSRF attacks. However, I 100% agree with you that adding a second defense mechanism (such as the Sec header, a custom "Protect-Me-From-Csrf: true" header, or if you have a really sensitive use case, cryptographically secure CSRF tokens) is a very good idea.

Thanks for correcting me - I see my web sec knowledge is getting rusty!

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