Telephony in Android 5.0.x before 5.0.2, 5.1.x before 5.1.1, 6.x before 2016-09-01, and 7.0 before 2016-09-01 allows attackers to cause a denial of service (loss of locked-screen 911 TTY functionality) via a crafted application that modifies the TTY mode by broadcasting an intent, aka internal bug 29832693.