Symantec Security Response
Android banking malware whitelists itself to stay connected with attackers
New Android.Fakebank.B variants use social engineering to bypass battery-saving process and stay active in background
Recent variants of Android.Fakebank.B have been updated to work around the battery-saving process Doze. Variants display a pop-up message asking the user to
add the threat to the battery optimisations exceptions whitelist. If this technique works, the malware stays connected
to command and control servers even when the device is dormant.
Bypassing Doze
Doze is a power-saving feature in Android 6.0 Marshmallow. When a user doesn’t use an unplugged device for a period of time,
the device enters Doze mode. This allows the OS to conserve battery by restricting apps' access to network and
CPU-intensive services. This feature is a hurdle for banking malware running in the background and connecting to an
attacker’s server to receive commands.
How the whitelisting technique works
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Figure 1 Code responsible for triggering Battery Optimisations exceptions whitelist pop-up
The permission required to fire this intent is REQUEST_IGNORE_BATTERY_OPTIMISATIONS which is classified as normal.
Marshmallow’s dynamic permission model defines permissions as either normal, dangerous, and above dangerous. Permissions
determined as normal are approved automatically and cannot be disabled through appinfo permissions.
The intent causes a pop-up message to appear, as shown in Figure 2. Users may be tricked into allowing the threat to
bypass Doze’s restrictions if the malware poses as a legitimate app.
Figure 2 Malware prompt claims that the app is called “Chrome” and requests whitelisting
Mitigation
Symantec recommends users follow these best practices to stay protected from mobile threats:
• Keep your software up to date
• Do not download apps from unfamiliar sites
• Only install apps from trusted sources
• Pay close attention to the permissions requested by apps
• Install a suitable mobile security app, such as Norton, to protect your device and data
• Make frequent backups of important data
Protection
Symantec and Norton products detect the threat discussed in this blog as Android.Fakebank.B.
For more information visit the Symantec Security Response blog post available here.