Twitter and OAuth Access Loophole
Brent Simmons brought up a great issue regarding the Twitter hack and the way OAuth works. Twitter’s notification to users:
Twitter believes that your account may have been compromised by a website or service not associated with Twitter. We’ve reset your password to prevent others from accessing your account.
And Brent’s response:
… would lead a normal person to believe that resetting your password would prevent other people from accessing your account in any way. But it’s not true, not if they’ve already accessed your account.
D’oh! I am betting most of you, like me, missed this subtlety. The issue is that if an attacker got to your account before the password was reset, the Twitter OAuth token they created for their own access will persist. That means that, despite a password reset, the attacker keeps access. Note that this is not intrinsic to OAuth – it is the choice in how the application platform (in this case Twitter) implements tokens. Some services, like Facebook, expire tokens by default. Twitter chose not to, but it’s not clear to most users (I certainly missed this point) that they should reset all Twitter apps if they are worried about a compromise.
Tokens change the way access works behind the scenes, and it’s not always clear how. In fact many application developers can specify ‘lifetime’ access tokens, overriding the application usage of OAuth if they choose. This is not a straightforward issue – more correctly, as David Mortman pointed out: “It’s a complex problem … actually, no, it’s a complex thought process due to the fact that we poorly educate users on the issues and what they need to do”.
If you got the email from Twitter, we advise you to go into the application sub-menu of your Twitter account and revoke any applications you see there. I understand when that retyping ginormous passwords in for every app on every mobile device is a pain, but it’s the only means we are aware of to invalidate old tokens and force re-authentication with the new password.
Nishant Kaushik goes into much more detail at Talking Identity.