Is this safe against cookie theft and replay attacks after expiry?

[allezxandre]

Hello! I'm looking into integrating this library into a project of mine, and I must start by saying that besides the package in itself which looks neat, the README is very well written and easy to follow. Thank you very much for the work!

I was wondering, what would prevent a malicious attacker from just getting a copy of the stateless session cookies produced by this package, and use it to access protected resources indefinitely in the future, regardless of the browser-enforced expiration?

I might be wrong, but from what I understand, expires is only used to set the Cookie Max Age, and it is not part of the encrypted/signed payload. So even though the Cookie payload is encrypted, any cookie will remain valid for as long as the server uses the same session secret, even after the actual non-malicious user generated new cookies.

One mitigation I see today is through the rotation of secrets, but this is impractical for low-activity applications that do not get deployed often, and have low enough traffic to not have to rotate their encryption secrets.

Another way to prevent this problem would be to add an expires attribute to the encrypted payload, but it feels a lot like re-importing concepts from JWTs, and suggests we might need to import other concepts from the JWT world like the issuer, the notBefore date, the subject, the audience, etc... (see here)

Or maybe there is some mechanism that I missed that prevents all that?

[pixelmund]

We already store the expires property in the saved cookie/payload https://github.com/pixelmund/svelte-kit-cookie-session/blob/728087b3787018eefe4feb07aadf09e4dfbd4340/src/lib/core.ts#L38

[pixelmund]

Here we verify if the date is expired https://github.com/pixelmund/svelte-kit-cookie-session/blob/728087b3787018eefe4feb07aadf09e4dfbd4340/src/lib/core.ts#L190

[allezxandre]

Awesome! I don't know how I missed that.

Cheers