In the bash shell was discovered a critical vulnerability

Existed for 22 years flaw allows to remote code execution. 
In the command shell bash, which is  popular in Linux sphere, was discovered a critical vulnerability that allows to remote code execution. According to the scale of the National Institute of Standards and Technology (NIST) it got 10 points.

Vulnerability CVE-2014-6271 is related to incorrect processing of environment variables and function definitions. It is worth noting that in the currently used versions of bash environment variable name and function is the same. In this case, the function definition begins with the characters () {.

Gap arises due to the fact that, after processing, shell does not stop and continues to parse the code and execute further commands of bash. This allows an attacker to use an environment variable with an arbitrary name for the delivery teams on the victim system.

Existed for 22 years CVE-2014-6271 was discovered last week by  IB-expert Stephane Chazelas, but the details were disclosed only now. The vulnerability is present in all versions of bash prior to 4.3. Corrections were released on Wednesday, 24-th of September.

Vulnerabilities allow to remote user to execute arbitrary code on the target system.

The vulnerability is caused due to an error processing the input data during parsing code. This can be exploited to execute arbitrary commands on the target system. The vulnerability is caused due to an error processing the input data during parsing code. This can be exploited to execute arbitrary commands on the target system.

 How the vulnerability can affect the user?

Bash and OS maintain a list of environment variables that describe the current user, the path to applications on the hard drive and other features. Created an environment variable with a particular structure, an attacker could execute arbitrary code on the victim's PC next time you will start bash. Create variable  environment you can in such way:

Establish a remote connection via SSH and try to log in. Picking a specific username or hostname, you can create an environment variable with the specific data;

· Forcing the user to create their own environment by himself;

· Forcing certain programs set the desired value of the environment variable. For example, the user is running a web-server and a script which installs its own environment variable. Even despite the fact that the work of the script does not change the system environment variables, the OS is already vulnerable.

Set your own environment variable, hackers will be able to execute arbitrary code on the user's device when you are going to start bash. The situation can become even more dangerous when you use sudo -s, triggering bash with its root privileges.

Note that some programs use bash to commit its own operations. Even if the user does not use bash, his PC may already have  been vulnerable.

Checking

In order to check whether the system is vulnerable, you must run in a terminal command:

env x = '() {:;}; echo vulnerable 'bash -c' echo hello '

If the system is protected by the user, bash returns the following message:

bash: warning: x: ignoring function definition attempt

bash: error importing function definition for `x '

hello

If the user's system is vulnerable, bash returns the following message:

vulnerable

hello

Correction

Developers Bash released an urgent fix for this vulnerability. All users of the operating system Linux (especially Ubuntu distributions and Debian) are advised to download the latest updates for this software.

Source : securitylab.ru