A variant of Mac No. 1 threat Shlayer since January already has been exploiting the vulnerability, which allows payloads to go unchecked through key OS security features. The vulnerability is particularly perilous to Mac users because it allows an attacker to very easily craft a macOS payload that goes unchecked by the strict security features built into the OS to keep malware out. Apple patched a zero-day vulnerability in its MacOS that can bypass critical anti-malware capabilities and which a variant of the notorious Mac threat has already been exploiting for several months.
Source: https://threatpost.com/apple-patches-macos-bug-bypass-defenses/165611/