To protect Android devices and users, we used Google Play Protect to disable Tizi-infected apps on affected devices and have notified users of all known affected devices. The developers’ accounts have been suspended from Play.
The Google Play Protect team also used information and signals from the Tizi apps to update Google’s on-device security services and the systems that search for PHAs. These enhancements have been enabled for all users of our security services and increases coverage for Google Play users and the rest of the Android ecosystem.
Additionally, there is more technical information below to help the security industry in our collective work against PHAs.
What do I need to do?
Through our investigation, we identified around 1,300 devices affected by Tizi. To reduce the chance of your device being affected by PHAs and other threats, we recommend these 5 basic steps:
Check permissions: Be cautious with apps that request unreasonable permissions. For example, a flashlight app shouldn’t need access to send SMS messages.
Update your device: Keep your device up-to-date with the latest security patches. Tizi exploited older and publicly known security vulnerabilities, so devices that have up-to-date security patches are less exposed to this kind of attack.
Locate your device: Practice finding your device, because you are far more likely to lose your device than install a PHA.
How does Tizi work?
The Google Play Protect team had previously classified some samples as spyware or backdoor PHAs without connecting them as a family. The early Tizi variants didn’t have rooting capabilities or obfuscation, but later variants did.
After gaining root, Tizi steals sensitive data from popular social media apps like Facebook, Twitter, WhatsApp, Viber, Skype, LinkedIn, and Telegram. It usually first contacts its command-and-control servers by sending an SMS with the device’s GPS coordinates to a specific number. Subsequent command-and-control communications are normally performed over regular HTTPS, though in some specific versions, Tizi uses the MQTT messaging protocol with a custom server. The backdoor contains various capabilities common to commercial spyware, such as recording calls from WhatsApp, Viber, and Skype; sending and receiving SMS messages; and accessing calendar events, call log, contacts, photos, Wi-Fi encryption keys, and a list of all installed apps. Tizi apps can also record ambient audio and take pictures without displaying the image on the device’s screen.
Tizi can root the device by exploiting one of the following local vulnerabilities:
Most of these vulnerabilities target older chipsets, devices, and Android versions. All of the listed vulnerabilities are fixed on devices with a security patch level of April 2016 or later, and most of them were patched considerably prior to this date. Devices with this patch level or later are far less exposed to Tizi’s capabilities. If a Tizi app is unable to take control of a device because the vulnerabilities it tries to use are are all patched, it will still attempt to perform some actions through the high level of permissions it asks the user to grant to it, mainly around reading and sending SMS messages and monitoring, redirecting, and preventing outgoing phone calls.
Samples uploaded to VirusTotal
To encourage further research in the security community, here are some sample applications embedding Tizi that were already on VirusTotal.