Race condition in the bindBackupAgent method in the ActivityManagerService in Android 4.4.4 allows local users with adb shell access to execute arbitrary code or any valid package as system by running "pm install" with the target apk, and simultaneously running a crafted script to process logcat's output looking for a dexopt line, which once found should execute bindBackupAgent with the uid member of the ApplicationInfo parameter set to 1000.
https://android.googlesource.com/platform/frameworks/base/+/a8f6d1b%5E%21/
http://www.securityfocus.com/bid/74213
http://www.securityfocus.com/archive/1/535296/100/1100/threaded