Perhaps unsurprisingly, a lot has been written about targeted attacks on Windows systems. Windows is, due to its popularity, the platform for which we discover most APT attack tools. At the same time, there’s a widely held opinion that Linux is a secure-by-default operating system that isn’t susceptible to malicious code. It’s certainly true that Linux hasn’t faced the deluge of viruses, worms and Trojans faced by those running Windows systems over the years. However, there is certainly malware for Linux – including PHP backdoors, rootkits and exploit code. Moreover, numbers can be misleading.
The strategic importance of servers running Linux makes them an attractive target for attackers of all kinds. If an attacker is able to compromise a server running Linux, they not only gain access to data stored on the server but can also target endpoints connected to it running Windows or macOS – for example, through a drive-by download. Furthermore, Linux computers are more likely to be left unprotected, so that such a compromise might well go unnoticed. When the Heartbleed and Shellshock vulnerabilities were first reported in 2014, two major concerns were that compromised Linux servers could become an attacker’s gateway into a corporate network and could give an attacker access to sensitive corporate data.