Shellshock allowed an unauthorized user to gain access to a server. It affected many Internet-facing services, which OS did it not directly affect?

Correct answer is: Linux

Shellshock (a.k.a. Bashdoor, Bash Bug, and CVE-2014-6271) is a security vulnerability discovered in September of 2014 that affected the Unix Bash shell found in most versions of Linux and Unix operating systems, including Mac OS X.