A privilege escalation vulnerability, nicknamed Dirty Cow and present in Linux since 2007, has been used in public attacks against web-facing Linux servers. Red Hat Security Strategist Josh Bressers said the vulnerability is serious but since it is not remotely exploitable, it s less critical than Heartbleed and other Internet-wide bugs admins have dealt with in the last two-plus years. The bug has been in the Linux kernel since version 2.6.22, released in 2007.
Source: https://threatpost.com/serious-dirty-cow-linux-vulnerability-under-attack/121448/