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Android clickjacking attacks possible from Google Play apps

Google implemented clickjacking attack mitigations in Android but left a potential avenue for malicious actors that won't be fixed until Android O is released.

Experts say Google's balancing act between security and usability on Android has left the door open for clickjacking attacks by malicious actors.

The threat of clickjacking attacks on Android were made "significantly more difficult" by Google with Android 6.0 Marshmallow, but new research from Check Point Software Technologies, based in Waltham Mass., shows that Google didn't completely remediate the issue.

The problem stems from a feature of Android that allows apps to write on top of other apps, which can lead to a number of abuses, according to Liviu Arsene, senior e-threat researcher at Romania-based antimalware firm Bitdefender.

"Apps that abuse the screen overlay function could trick the user into giving away sensitive information -- passwords, credentials, etc. -- by overlaying phishing screens on top of legitimate applications," Arsene told SearchSecurity. "If convincing enough, those phishing screens could be leveraged to get users to uninstall applications, remove security software, install other malicious applications, or even give away banking information, as what they would see on the screen would be manipulated by the malicious app."

The Check Point Mobile Research Team noted that Google did introduce a new permission model in Android 6.0 which made it more difficult to exploit this issue, but only for apps installed outside of the Google Play Store.

"Since Google understood the problematic nature of this permission, and the apparent risks for user privacy it created the distinct process mentioned above to approve it. However, this soon caused problems, as this permission is also used by legitimate apps, such as Facebook, which requires it for its Messenger chat heads feature," Check Point wrote in a blog post. "As a temporary solution, Google applied a patch in Android version 6.0.1 that allows the Play Store app to grant run-time permissions, which are later used to grant SYSTEM_ALERT_WINDOW permission to apps installed from the app store. This means that a malicious app downloaded directly from the app store will be automatically granted this dangerous permission."

Yair Amit, CTO at Skycure, a mobile security company headquartered in Palo Alto, Calif., called this "a classical trade-off between usability and security."

"Google's policy to allow easier ways to use the screen overlay makes the experience of downloading and using apps that come from Google Play more streamlined, but since malware can enter into Google Play, this creates a security exposure for users," Amit told SearchSecurity. However, Amit said the Google Play Store uses "strong app analysis technology, which combines static and dynamic analysis. While it blocks, the wide variety of malware campaigns that have been uncovered in the past few years illustrates that Google's great efforts need to be supplemented by security solutions."

Arsene said using this permission model does allow Google stricter control but doesn't eliminate the potential for clickjacking attacks, especially for those without access to the Google Play Store.

"Google's Bouncer is not immune to falsely tagging malicious apps as legitimate. There have been numerous instances in the past when malicious applications made their way in Google Play and eventually on user devices," Arsene said. "Plus, there are plenty of third-party app marketplaces out there from where users can still download and install potentially malicious apps. And not because they're necessarily bent on using those marketplaces, but because Google Play may be restricted in their respective region and third-party marketplaces are their only choice."

Check Point reached out to Google regarding clickjacking attack issues from these permissions and Google said it was working on the issue and would fix the issue in Android O. Android O will likely be shown off in beta form next week at the Google I/O conference, but the full release traditionally doesn't begin until late fall.

Matthew Gardiner, cybersecurity strategist at Mimecast, said when to push a patch can be a difficult decision.

"This is a typical challenge in the vulnerability patching world for application and OS developers. Patching things quickly can risk the stability of their system and patching things slowly risks further exploitation of the vulnerability by cybercriminals," Gardiner told SearchSecurity. "It's a tough call all around, but something that most developer teams wrestle with every day."

Arsene worried about those who may never get the Android O update, but said there were other ways to protect against clickjacking attacks.

"Having a fix only available for Android O does raise security concerns, as a large number of Android users will be left vulnerable throughout their entire lifetime," Arsene said. "However, having security software installed that's able to spot malicious applications is a great way of minimizing the risk of accidentally installing malicious apps that leverage the screen overlay function, even if these apps are downloaded from third-party marketplaces."

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