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Shellshock is an [[arbitrary code execution]] vulnerability that offers a way for users of a system to execute commands that should be unavailable to them. This happens through Bash's "function export" feature, whereby one Bash [[process (computing)|process]] can share command scripts with other Bash processes that it executes.<ref>{{cite web|url=https://www.gnu.org/software/bash/manual/bash.html#Shell-Functions|title= Bash Reference Manual: Shell Functions |access-date= 2 October 2014}}</ref> This feature is implemented by encoding the scripts in a table that is shared between the processes, known as the [[environment variable]] list. Each new Bash process scans this table for encoded scripts, assembles each one into a command that defines that script in the new process, and executes that command.<ref name="exported-function">{{cite web|url= http://git.savannah.gnu.org/cgit/bash.git/tree/variables.c?id=ac50fbac377e32b98d2de396f016ea81e8ee9961#n315 |title=Bash 4.3 source code, file variables.c, lines 315-388 |access-date= 2 October 2014}}</ref> The new process assumes that the scripts found in the list come from another Bash process, but it cannot verify this, nor can it verify that the command that it has built is a properly formed script definition. Therefore, an attacker can execute arbitrary commands on the system or exploit other bugs that may exist in Bash's command interpreter, if the attacker has a way to manipulate the environment variable list and then cause Bash to run. At the time the bug was discovered, Bash was installed on [[macOS]] and many [[Linux]] operating systems as the main command interpreter, so that any program that used the <code>system</code> function to run any other program would use Bash to do so.
The presence of the bug was announced to the public on 2014-09-24, when Bash updates with the fix were ready for distribution,<ref name="seclist-q3-666"
==Reports of attacks==
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