[ALUG] Critical bug in bash: remote code execution

[Andreas Tauscher]

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A critical bug [1] allows to execute any code. Anything an attacker
has to do is setting a special environment variable.
All major distributions have already released updates.

To take advantage of the bug access to bash is needed. For example if
the ssh access is limited this limitations can be bypassed.
Also webservers using bash scripts as CGI are vulnerable.

Form the RedHat blog [2] is this short script to test if your version
of bash is vulnerable:
env x='() { :;}; echo OOPS' bash -c /bin/true

How is this working:
The attacker is defining within the variable x a function. Ok, nothing
serious. But bash does after this definition not stop to parse code.

On a vulnerable bash you will get the output OOPS
A fixed bash will quit with an error:
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'

Andreas

[1] https://access.redhat.com/security/cve/CVE-2014-6271
[2]
http://community.redhat.com/blog/2014/09/critical-bash-security-vulnerability-update-your-systems-today/

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