A newly-discovered vulnerability in iOS Mail can be used to attack an iPhone remotely using a malicious e-mail message, even if you’re running the latest version of iOS (13.44.1) The way the attack works is that the threat actor sends an email message designed to cause a buffer overflow in Mail (or maild) A buffer overflow is a bug in code that allows an attack to happen if the attacker is able to fill a block of memory beyond its capacity. Once an attack is successful, the attacker would presumably use access to the Mail app to delete these messages.”]
Source: https://blog.malwarebytes.com/mac/2020/04/ios-mail-bug-allows-remote-zero-click-attacks/