On October 21, 2016, a privilege escalation vulnerability in the Linux kernel was disclosed. The bug is nicknamed Dirty COW because the underlying issue was a race condition in the way kernel handles copy-on-write (COW). Exploiting this bug means that a regular, unprivileged user on your server can gain write access to any file they can read, and can therefore increase their privileges on the system. This tutorial explains how to protect your server from this vulnerability.