SHELL-SHOCK (BASH-DOOR)

Shell-shock, also known as Bash-door,  is a family of security bugs in the Unix Bash shell, the first of which was disclosed on 24 September 2014. Shell-shock could enable an attacker to cause Bash to execute arbitrary commands and gain unauthorized access to many Internet-facing services, such as web servers, that use Bash to process requests.


What is Shell-shock / Bash Bug / Bash Door?

To understand the bug, we need to look at what ‘BASH’ is. Bash (Bourne Again Shell) is a Unix Shell. Brian Fox wrote it as a part of GNU project to replace Bourne shell. While most users don’t come in contact with Bash, programmers know that Bash can be used to issue commands to a UNIX-based computer using text inputs in a text window. More importantly, Bash acts a command interpreter and runs commands passed to it by applications.

There is a loophole in Bash that hackers can potentially exploit to gain control over a target computer. As the vulnerability affects Bash, the bug is also known as Bash Bug or Bash Door. After the first bug was uncovered, several other bugs from the same family have also been discovered.

How can hackers exploit this bug?

Exploiting the loophole, hackers can inject commands in the systems without authentication. This can help malicious users get a foothold in the system. After initial access the hacker can set environment variables to get more privileges and could theoretically even gain root access. Symantec’s graphic shows how it works: