7 ms·

Leaking your auth tokens through XSS sucks more.

by kadfak 5y ago

leipert 5y ago
I don’t know whether you are referring to only local and session storage being feasible or not, but on can access cookies from JS as well.
- AlbinoDrought 5y ago
  Normal cookies are JS-accessible, but HTTP-only cookies should not be: "A cookie with the HttpOnly attribute is inaccessible to the JavaScript Document.cookie API; it is sent only to the server." https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#restrict_access_to_cookies https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#re...
  - leipert 5y ago
    Ah thanks! This is new to me. That is indeed a concern, but probably can be worked around, e.g. by proxying requests to third party domains through the same Domain.
    - kreetx 5y ago
      You can't make the browser to send you cookies for other origins so you won't be able to use them from your server.
- fractionalhare 5y ago
  Which is why you use domain scoping, httpOnly and Secure cookie flags so they can only be read by matching hosts (with greater granularity than same-origin policy) over HTTPS and can’t be read by JavaScript. The Web Storage API does not offer these protections.
  - dkarras 5y ago
    They can't be read BUT the browser will send the cookie with every request. If you have an XSS, it is game over. The attacker can just send requests from your browser. Slightly less convenient. You are merely taking away the convenience of the attacker doing the attack manually on his own browser, which he probably doesn't want to do anyways. If he can inject js into your site, he will make your browser send the request(s) to do the actions with your credentials in an automated and quick way. Your browser will send the cookie automatically. From the attacker, it would merely be nice if he could read your tokens, but it is absolutely not necessary. Like some here, I don't understand the hate around keeping tokens in localstorage. People immediately say "but js can read it!" but so what? If someone can put malicious js in my site, it is GAME OVER, secure http-only cookie or not. When that is the case, the saner option is doing away with an old and misused invention called cookies. The upside with ditching cookies is that you are an order of magnitude safer against CSRF since your browser does not send anything automatically. You don't need to keep CSRF token state in your server(s) either (helps with scale, one less state to worry about), it is a win. http-only secure cookies do not give you any additional security. Ditching cookies does.
    - anaphor 5y ago
      I think some people don't realize that CSRF tokens are basically the same thing as bearer tokens (which JWT also does), but it's just that they get re-generated every time you open a new page usually. So it's a bit ironic when everyone screams that tokens are bad, but they're all using them to protect against confused deputy attacks.
    - shock-value 5y ago
      A good option is doing both. Store a security token in localStorage and additionally store a secure signature for it in a secure, HTTP-only cookie. On your backend, verify validity of both the token and its additional signature contained in the cookie.
      - dkarras 5y ago
        I don't believe it adds any meaningful security that justifies the cost (development, testing, hardening, scaling the state across servers if necessary etc.) With security "more complicated" does not necessarily mean "more secure". Doing it without multiplying the number of ways things can go wrong is deceptively hard.
asabil 5y ago
If you have an xss your problem is much bigger than leaking an ephemeral access token through localStorage

Leaking your auth tokens through XSS sucks more.

by kadfak 5y ago

Leaking your auth tokens through XSS sucks more.

I don’t know whether you are referring to only local and session storage being feasible or not, but on can access cookies from JS as well.

AlbinoDrought 5y ago
Normal cookies are JS-accessible, but HTTP-only cookies should not be: "A cookie with the HttpOnly attribute is inaccessible to the JavaScript Document.cookie API; it is sent only to the server." https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#restrict_access_to_cookies https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies#re...
- leipert 5y ago
  Ah thanks! This is new to me. That is indeed a concern, but probably can be worked around, e.g. by proxying requests to third party domains through the same Domain.
  - kreetx 5y ago
    You can't make the browser to send you cookies for other origins so you won't be able to use them from your server.
fractionalhare 5y ago
Which is why you use domain scoping, httpOnly and Secure cookie flags so they can only be read by matching hosts (with greater granularity than same-origin policy) over HTTPS and can’t be read by JavaScript. The Web Storage API does not offer these protections.
- dkarras 5y ago
  They can't be read BUT the browser will send the cookie with every request. If you have an XSS, it is game over. The attacker can just send requests from your browser. Slightly less convenient. You are merely taking away the convenience of the attacker doing the attack manually on his own browser, which he probably doesn't want to do anyways. If he can inject js into your site, he will make your browser send the request(s) to do the actions with your credentials in an automated and quick way. Your browser will send the cookie automatically. From the attacker, it would merely be nice if he could read your tokens, but it is absolutely not necessary. Like some here, I don't understand the hate around keeping tokens in localstorage. People immediately say "but js can read it!" but so what? If someone can put malicious js in my site, it is GAME OVER, secure http-only cookie or not. When that is the case, the saner option is doing away with an old and misused invention called cookies. The upside with ditching cookies is that you are an order of magnitude safer against CSRF since your browser does not send anything automatically. You don't need to keep CSRF token state in your server(s) either (helps with scale, one less state to worry about), it is a win. http-only secure cookies do not give you any additional security. Ditching cookies does.
  - anaphor 5y ago
    I think some people don't realize that CSRF tokens are basically the same thing as bearer tokens (which JWT also does), but it's just that they get re-generated every time you open a new page usually. So it's a bit ironic when everyone screams that tokens are bad, but they're all using them to protect against confused deputy attacks.
  - shock-value 5y ago
    A good option is doing both. Store a security token in localStorage and additionally store a secure signature for it in a secure, HTTP-only cookie. On your backend, verify validity of both the token and its additional signature contained in the cookie.
    - dkarras 5y ago
      I don't believe it adds any meaningful security that justifies the cost (development, testing, hardening, scaling the state across servers if necessary etc.) With security "more complicated" does not necessarily mean "more secure". Doing it without multiplying the number of ways things can go wrong is deceptively hard.

asabil 5y ago

If you have an xss your problem is much bigger than leaking an ephemeral access token through localStorage