Fix remote exploit vulnerability in bash

Written by on

If you're using Prestashop / Magento / Opencart for your bussiness, i know you need ( and maybe you have ) a server for your business. Redhat, CentOS, Ubuntu...,hmm, something like that.

But now, a remotely exploitable vulnerability has been discovered in bash on Linux and it is unpleasant. This affects Debian as well as other Linux distributions. You will need to patch ASAP.

 An attacker could inject and subsequently execute arbitrary shell commands in applications or services that call bash. The major attack vectors that have been identified in this case are HTTP requests and CGI scripts. Certain services and applications allow remote unauthenticated attackers to provide environment variables, allowing them to exploit this issue.

How to Fix

To test if your version of Bash is vulnerable to this issue, run the following command:

$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"

If the output of the above command looks as follows:

vulnerable
this is a test

That means you are using a vulnerable version of Bash. The patch used to fix this issue ensures that no code is allowed after the end of a Bash function.

Thus, if you run the above example with the patched version of Bash, you should get an output similar to:

$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
this is a test

Fix this bug now :

$ apt-get update
$ apt-get --only-upgrade install bash

You should check once again to make sure everything is ok :))