Hot to check if your Linux server is vulnerable regarding the BASH bug?
Just type this command in your SSH shell
$ env x='() { :;}; echo vulnerable' bash -c 'echo hello'
If you got this output then you are safe:
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
hello
If you got this output then you are vulnerable and need to update:
vulnerable
Here is the tutorial how to do it:
https://brew.sh/