A vulnerability in millions of fully patched Android phones is being actively exploited by malware that’s designed to drain the bank accounts of infected users, researchers said on Monday.
The vulnerability allows malicious apps to masquerade as legitimate apps that targets have already installed and come to trust, researchers from security firm Promon reported in a post. Running under the guise of trusted apps already installed, the malicious apps can then request permissions to carry out sensitive tasks, such as recording audio or video, taking photos, reading text messages or phishing login credentials. Targets who click yes to the request are then compromised.
Researchers with Lookout, a mobile security provider and a Promon partner, reported last week that they found 36 apps exploiting the spoofing vulnerability. The malicious apps included variants of the BankBot banking trojan. BankBot has been active since 2017, and apps from the malware family have been caught repeatedly infiltrating the Google Play Market.
The vulnerability is most serious in versions 6 through 10, which (according to Statista) account for about 80% of Android phones worldwide. Attacks against those versions allow malicious apps to ask for permissions while posing as legitimate apps. There’s no limit to the permissions these malicious apps can seek. Access to text messages, photos, the microphone, camera, and GPS are some of the permissions that are possible. A user’s only defense is to click “no” to the requests.
An affinity for multitasking
The vulnerability is found in a function known as TaskAffinity, a multitasking feature that allows apps to assume the identity of other apps or tasks running in the multitasking environment. Malicious apps can exploit this functionality by setting the TaskAffinity for one or more of its activities to match a package name of a trusted third-party app. By either combining the spoofed activity with an additional allowTaskReparenting activity or launching the malicious activity with an Intent.FLAG_ACTIVITY_NEW_TASK, the malicious apps will be placed inside and on top of the targeted task.
“Thus the malicious activity hijacks the target’s task,” Promon researchers wrote. “The next time the target app is launched from Launcher, the hijacked task will be brought to the front and the malicious activity will be visible. The malicious app then only needs to appear like the target app to successfully launch sophisticated attacks against the user. It is possible to hijack such a task before the target app has even been installed.”
Promon said Google has removed malicious apps from its Play Market, but, so far, the vulnerability appears to be unfixed in all versions of Android. Promon is calling the vulnerability “StrandHogg,” an old Norse term for the Viking tactic of raiding coastal areas to plunder and hold people for ransom. Neither Promon nor Lookout identified the names of the malicious apps. That omission makes it hard for people to know if they are or were infected.
Suspicious signs include:
- An app or service that you’re already logged into is asking for a login.
- Permission popups that don’t contain an app name.
- Permissions asked from an app that shouldn’t require or need the permissions it asks for. For example, a calculator app asking for GPS permission.
- Typos and mistakes in the user interface.
- Buttons and links in the user interface that do nothing when clicked on.
- Back button does not work as expected.