Outlook.com Cookie Hijacking Issue

Whoops, it looks like somebody has uncovered another potential security problem for Outlook.com and Hotmail.com users …

Users of outlook.com or hotmail.com, Microsoft’s two email services, should take note now. Information are stored in cookies when you use the site including whether you have successfully authorized your account or not. If the information is available, you can open and close both services without having to log in again to one of them. That’s great as it is comfortable, but also problematic as it means that someone else can copy that cookie from your system to access your email account online without re-authorization.

What makes this particularly worrying is that logging out of the services does not invalidate the session information stored in the cookie. If someone exports the cookie when the session is still active, it continues to work after the user logged out on the PC and invalidated the session information saved to the cookie.

Here is a – silent – demo video that demonstrates how this works.

Note that the researchers are using the two add-ons Cookie Importer and Cookie Exporter for the Firefox web browser to export and import cookies on the fly.

The steps to reproduce the vulnerability as outlined by the researchers:

  1. Sign in to Outlook.com or Hotmail.com.
  2. Export the cookie that gets created during the process to your system. You can use the Firefox add-on for that, another browser extension or simply copy the cookie manually from the directory it has been stored in.
  3. Log out of Outlook or Hotmail.
  4. Import the cookie into another browser either by using the suggested Firefox extension, another browser add-on or manually copying it into the right directory.
  5. Load the outlook.com or hotmail.com website. You should notice that you are logged in automatically thanks to the cookie that you saved earlier.

Microsoft notes that some highly sensitive options on the site require re-authorization. This is for instance the case when you try to change the account password. What attackers can do however is read and send emails, delete emails or use other information that are lined to email accounts like resetting passwords for online services.

One could now say that physical access to the system is required to exploit this vulnerability and that’s certainly correct up to a point. There may be other means to exploit this though, over a local network for instance or with the help of malware that exports session cookies and sends the data to the attacker.

It needs to be noted that Microsoft is not the only company that is affected by this. Google Drive for example faces a similar issue. When the software is running, you can click on links to open the Google Account on the web without re-authentication.

Can you protect your account against this attack? Not really. Email programs may help but the programs may not be available on all systems you work with. (via)

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