Thursday, November 29, 2012

XSS + "Save your password" = pwned

(on HNews)
Basically, browsers often suggest you to save your password and prefill it automatically.

The bug I just discovered: This value can be retrieved from JS side easily(and this means XSS can steal it). Your REAL password. It's not fucking yet-another-CSRF or SQL injection(server side is pwned) or other trivial. YOU are pwned.  Kind of a serious issue.

Very similar to old issue with 'highlighted' visited links, when attacker could know did you visit certain link or not.

Also, XSS can be on any page and user can be signed in or signed out. It will just open iframe or window and get values because of same origin.


Browsers should deny access to prefilled passwords from JS.(UPD: not helpful)

P.S. I'm alive and in Asia(now Kuala Lumpur). Don't worry, new stuff will be published soon ;)

I WAS WRONG. (About these two things)

1. Proposed solution will break the AJAX-based authentications since JS will not have access to password anymore. For example you might want to send password in a header:
Authentication: username:password
and to do so you have to use XHR. If you cannot retrieve password from autofilled input authentication will get broken.

2. There is one more workaround - XSS can change 'action' field to 3rd party website and then .submit(). JS doesn't need access to .value - browser itself will send it to attacker's server. Should we restrict sending passwords only to actions on the current page domain(same origin)? Sounds ugly.

Possible solutions:
1. restricting 'action' value to same origin. Ugly?
2. using Autocomplete only when user is interacting with the website e.g. by typing the first letters of the nickname.
3. Ask in the top bar notification "Should we use autocomplete on" or smth like this. Looks not bad to me.

4. BEST ONE: do not use any autofill. At least for passwords.
Because security of autofills is fucked. The more websites you use - the more probability to be XSSed on the one of them.