Monday, March 28, 2016

What is ShellShock ?

ShellShock is a security vulnerability which affects many versions of Unix like Operating Systems like Linux and results in allowing attackers to gain control over a system illegitimately.

ShellShock Vulnerability

In Unix, Shell is a command processor using which commands are executed in the Opetating Systems. Bash is one such command processor. It is mainly used in text windows, but many applications also can use it to execute required commands.

Environment Variables are variables whose values are used to affect the way the running processes will behave in the computer. For example, an application process may prefer to store temporary files in a folder. For that purpose, the running process will check the value of the Environment Variable called TEMP and store the files there.

Using ShellShock vulnerability, an attacker can attach malicious code to some Environment Variable in Bash and run it to gain control over the system.


Many a times Web Servers use Bash to execute commands. So, the attackers can exploit this vulnerability to execute malicious commands in a Web Server. And, the results of that may be as serious as exposing sensitive files like password files to the attackers or downloading malicious files to the Web Servers.

Even other devices like Linux based routers that use CGI for Web Interfaces are vulnerable to tthis attack. Attackers can exploit ShellShock vulnerability and use CGI to execute malicious commands in those devices.

IoT (Internet of Things) devices also may be vulnerable to this attack if they are using Bash.

OpenSSH Servers are also vulnerable to this attack. Attackers can gain unrestricted shell access of the server exploiting ShellShock.

Other than that, Computers running Mac OS X, DHCP Clients, Qmail Server and IBM HMC restricted shell are also vulnerable to this attack.


There are a number of reports of exploitation of this vulnerability by the attackers. But, the good news is that a number of Operating Systems vendors who are affected by this vulnerability have already issued patches. Website owners and business owners should apply those latest security patches to their Operating Systems to avoid ShellShock Attack.

However, users are also advised to apply recent security patches for their web enabled devices like routers, IoT devices and embedded devices etc to prevent this attack.

So, beware of various security vulnerabilities, so that you can protect yourself in a better way. And, stay safe, stay secured.

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