The vulnerability called Time-of-Check to Time-of-Use (TOCTTOU) was discovered by Palo Alto in January last year. In simple words, it hijacks your device while the installation of an application and installs malware instead of the application.
The malware has been linked to people who frequent and download often from third party application stores that download an application you want to install, in the local storage area of your phone, rather than the protected area where the Play Store downloads and installs its applications from.
Google's security team was informed of the vulnerability a month after it was found by Palo Alto. It can be used by hackers to exploit an android running device in various manners, with credit card information of users also being at risk.
The vulnerability has existed for an year according to Palo Alto's Disclosure Timeline and measures like vulnerability scanners have been put in place to mitigate this vulnerability.