Researchers have discovered what they say is a design flaw in Android that could be used by criminals to steal data via phishing or by advertisers to bring annoying pop-up ads to phones.
Developers can create apps that appear to be innocuous but which can display a fake bank app log-in page, for instance, when the user is using the legitimate bank app, Nicholas Percoco, senior vice president and head of SpiderLabs at Trustwave, said ahead of his presentation on the research at the DefCon hacker conference today.
Currently, apps that want to communicate with the user while a different app is being viewed just push an alert to the notification bar on the top of the screen. But there is an application programming interface in Android's Software Development Kit that can be used to push a particular app to the foreground, he said.
"Android allows you to override the standard for (hitting) the back buttons," said Sean Schulte, SSL (Secure Sockets Layer) developer at Trustwave.
"Because of that, the app is able to steal the focus and you're not able to hit the back button to exit out," Percoco said, adding that they've named the issue the Focus Stealing Vulnerability.
The researchers have created a proof-of-concept tool that is a game but also triggers fake displays for Facebook, Amazon, Google Voice, and the Google e-mail client. The tool installs itself as part of a payload inside a legitimate app and registers as a service so it comes back up after the phone reboots, Percoco said.
In a demo showing a user opening up the app and seeing the log-in screen for Facebook, the only indication that something odd has happened is a screen blip so quick many users wouldn't notice. The fake screen completely replaces the legitimate one, so a user wouldn't be able to tell that anything is out of place.
With this design flaw, game or app developers can create targeted pop-up ads, Percoco said. The ads could be merely annoying, like most pop-ups are, but they could also be targeted to pop up an ad when a competitor's app is being used, he added.
"So the whole world of ads fighting with each other on the screen is possible now," said Percoco, who demonstrated an Android rootkit at DefCon last year.
The functionality would not raise any red flags in the permissions displayed when the user downloads the app because it is a legitimate function for apps to check the phone state in what is called the Activity Service, according to Schulte.
Percoco said the researchers spoke to someone at Google about their findings a few weeks ago and that the individual acknowledged that there was an issue and said the company was trying to figure out how to address it without breaking any functionality of legitimate apps that may be using it.
When contacted for comment, a Google representative said he would look into the matter.