Mobile applications seeking to bypass 2FA in order to hijack a victim's device used to often ask for the permissions required to seize control of SMS settings, which would allow the malicious software to intercept 2FA codes designed to add a secondary layer of security to online accounts.
Earlier this year, Google restricted SMS and Call Log permissions in Android to stop developers from gaining access to these sensitive permissions without personally making their case in front of the tech giant first.
The crackdown caused chaos for some legitimate developers whose apps were suddenly at risk of losing useful features. When it came to malicious apps, however, the change in Google's policies stripped many of the options available to abuse SMS and Call Log controls to bypass 2FA.
In the apps found by ESET, the developer has come up with a way to circumvent Google's changes.
The first app was uploaded to Google Play on June 7, 2019, under the developer and application name "BTCTurk Pro Beta." The second, named "BtcTurk Pro Beta," falls under the developer name "BtSoft."
After one of these applications has been downloaded and launched, the software requests a permission called Notification access which gives the app the power to read notifications displayed by other apps on the device, to dismiss them, or to click any buttons they contain.
The app then shows a fake login request to access the Turkish cryptocurrency platform. If credentials are submitted, an error page is played while the account credentials are whisked away to the attacker's command-and-control (C2) server.
"Instead of intercepting SMS messages to bypass 2FA protection on users' accounts and transactions, these malicious apps take the OTP from notifications appearing on the compromised device's display," ESET says. "Besides reading the 2FA notifications, the apps can also dismiss them to prevent victims from noticing fraudulent transactions happening."
The malicious apps also have filters in place while scanning notifications on the lock screen and so only alerts of interest are targeted. Keywords include "mail," "outlook," "sms," and "messaging."
The technique is new and effective but only to the point of how much information can be stolen from a notification box. The OTP may not be fully shown in a mobile notification pop-up, and while the interception method could also theoretically be used to grab email-based one-time passwords, message lengths vary and so the attack vector may not always be successful.
Thankfully, fewer than 100 users are believed to have installed the apps before they were reported to Google on June 12 and removed. However, as the Notification access permission was introduced in Android 4.3, the security team has suggested that the 2FA bypass technique could affect "almost all active Android devices."
Many of 2018's most dangerous Android and iOS security flaws still threaten your mobile security