re: How to securely store JWT tokens. VIEW POST

re: If you use CSP to block any inline-script/insecure-script and also enforce that only trusted JS files must be accepted: there's no issue about usin...

Hello Lucas. I agree that this way you would be protected by scripts that are not hosted in your own domain. But in case there is, for example, a node module that you installed while developing it would be considered insecure. I understand your point and it is 100% valid. But with this approach, even in the rare case that a module was vulnerable and you had by accident injected it in your base app, the module could never send the token to an external domain through an Ajax request. It could only hit your internal API, but this would require that the attacker had injected malicious code in a node module just to attack your web application specifically. Let me know about your thoughts.


That is not true. With javascript you can just create a tag with an src to the attacker sites - and as we know the browser always sends the cookie with the requests - so bingo the attacker now has your cookie. Please beware of that

Hey Milebroke,

Not sure which comment you wanted to leave a reply. If you refer to cookies, in the case of Lax and Strict they won't be sent to the attacker's website if we, for example, inject an image with the attackers URL as the source. That's because it's not considered a first level navigation event.

Although, it may be sent if the attacker creates a GET form and sends it by clicking the button through javascript. I have to admit that I have not tested this scenario, but you will be fine if you just use Strict flag, as it will prevent all cross domain cookie sharing.


I don't know. That issue about leak the session can also be fixed with CSP, since you can block external communications too. I never use node modules, and you might guess why, so I can't say anything about it.

What I'm saying is that it is easy to find solutions when you have such a small attack surface, and never tell it. You can also suggest encrypting the local storage value using a random key using, with a random algorithm with a random name... Yes, attackers can extract the key (...), but then use the same argument: "just to attack your web application specifically". The opposite scenario might be valid: since I'm considering that the page is secure against XSS, then I can use LocalStorage.

I think it would be better if it compares all alternatives (SessionStorage, LocalStorage, Cookies, Credential Management API, IndexedDB API) and all kinds of known attacks.

So you suggest serving external js from another domain and set a CSP to disallow these scripts to access local storage or make ajax requests?

That’s correct. But if you serve external scripts through a CDN for example, and set a csp you are secure with the cookie implementation too. I may write a complementary article or extend this one at some point. Thanks for your feedback its really valuable!!!

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