CVE-2020-9885
An issue existed in the handling of iMessage tapbacks. The issue was resolved with additional verification. This issue is fixed in iOS 13.6 and iPadOS 13.6, macOS Catalina 10.15.6, tvOS 13.4.8, watchOS 6.2.8. A user that is removed from an iMessage group could rejoin the group.
Source: CVE-2020-9885