A new and previously undetected critical vulnerability in SIM cards could allow remote attackers to compromise targeted mobile phones and spy on victims just by sending an SMS. The vulnerability resides in a piece of software, called the(a dynamic SIM toolkit), embedded on most SIM cards that is widely being used by mobile operators in at least 30 countries. A specific private company that works with governments is actively exploiting the SimJacker vulnerability from at least the last two years to conduct targeted surveillance on mobile phone users across several countries.
Source: https://thehackernews.com/2019/09/simjacker-mobile-hacking.html