This vulnerability allows an app to install any number of apps with any type of permissions without user’s explicit consent. It is based on two things:
- You can install an app from Google Play using just the browser, even from PC, take a look here.
- An app can embed a browser and automatically login into your Google account without any notification, using a few permissions.
One can build an Android app, let’s call it Trojan, that requires these permissions:
- android.permission.INTERNET - Allows applications to open network sockets.
- android.permission.GET_ACCOUNTS - Allows access to the list of accounts in the Accounts Service.
- android.permission.USE_CREDENTIALS - Allows an application to request authtokens from the AccountManager.
These are the steps to reproduce it:
- Trojan app contains a WebView that will automatically login into user’s Google account by requesting authtokens from the Account Manager, user will not be notified nor have any way to stop this.
- Using this information it can issue a request to install ANY app on Google Play, on EVERY device registered with that Google account. The user will not be prompted and will not have any way to stop this.
- Trojan app could be full screen and the user will not even see the install notification.
- Trojan app could choose to install the app on a different device, from the devices registered with the Google account, the user will not see anything unusual on the current device where the Trojan runs.
- The installed app can have access to ALL permissions (if it specifies so in the manifest) without the user explicitly approving that, it could have access to services that cost you money, like sending SMS or making phone calls, manage accounts, disable your phone, just look at the permission list.
- Since you have access to all Google data for that account, there are other scenarios, like accessing emails and more, but the PoC did not address those.
The Google fix, as far as I could tell, was to not allow the browser to automatically login. Instead, the user will be prompted with a text that says it would allow the app to have access to all Google data. This however does not inform the user that it will allow automatic installation of any app, potentially causing direct and immediate loss of money.
I will not release the PoC, I think it would be too easy to cause real damage. However it is not that difficult to implement.
Vendor contact timeline
- 2013-12-16 – Contact security(at)google.com.
- 2013-12-17 – Received reply that the issues was passed to security(at)android.com.
- 2013-12-20 – Received reply that they could not reproduce the issue.
- 2013-12-20 – Sent a stripped down version of the PoC, not much different.
- 2014-01-16 – Request status update.
- 2014-01-24 – Received response that the rollout of the fix started last week.
- 2014-02-12 – Received response that the fix is live for 100% users/devices.