The vulnerability affects all Android 4.x firmware versions on Google Galaxy Nexus, Nexus 4 and Nexus 5. The problem is with how the phones handle a special type of text message, known as a flash SMS. By sending around 30 Flash SMS messages to Nexus phones an attacker can cause the phone to malfunction. Google is aware of the situation, and says that it’s investigating things. Until the fix from Google lands, users can use the free Class0Firewall app to prevent such situations.
Source: https://thehackernews.com/2013/11/Flash-sms-dos-attack-Google-Nexus.html