The value of a security vulnerability drops significantly the moment it gets patched but the bad guys will keep exploiting it for as long as they can find victims that are worth the effort. Some of the most exploited security bugs in the first quarter of 2019 were well-known, old problems, some of them patched almost a decade ago. The most prevalent are the following: CVE-2017-8570 – “Composite Moniker”” remote code execution in Microsoft Excel/Word used in operation “”Red October”” exploit.”
Source: https://www.bleepingcomputer.com/news/security/old-vulnerabilities-are-still-good-tricks-for-todays-attacks/