First announced almost a month ago, Shellshock continues to endanger un-patched web servers and Linux devices. So what is it? How can you tell if you’re vulnerable? And how can it be addressed?
What Is Shellshock?
Shellshock is a vulnerability in the bash software program. Bash is a shell, installed to Linux and other operating systems in the Unix family. A shell is a software component that is deeply integrated into the operating system, which is what makes this vulnerability so insidious.
The Shellshock vulnerability is a bug in the parser. It was first introduced more than 20 years ago when a feature to allow exporting functions was added. The danger is that an attacker who could control the content of an environment variable could potentially execute arbitrary code on a vulnerable system. Remote code execution (RCE) vulnerabilities (also called “arbitrary code execution” vulnerabilities) are among the most dangerous. Paired with privilege escalation vulnerabilities or poor security practices (e.g. allowing web servers to run as privileged users), unaddressed arbitrary code execution vulnerabilities can lead to the complete takeover of vulnerable systems.