"The vulnerability looks pretty awful at first glance, but most systems with
Bash installed will NOT be remotely exploitable as a result of this issue,"
Ellis writes. "In order to exploit this flaw, an attacker would need the
ability to send a malicious environment variable to a program interacting with
the network and this program would have to be implemented in Bash, or spawn a
sub-command using Bash."
How to tell if you're vulnerable
Beyond Linux-based systems, Graham and Ars Technica report that Mac OS X
Mavericks contains a vulnerable version of Bash.
To test if your version of Bash is vulnerable to this issue, Red Hat says to
run this command:
$ env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
If the system responds with the following, then you're running a vulnerable
version of Bash and you should apply any available updates immediately:
vulnerable
this is a test
"The patch used to fix this issue ensures that no code is allowed after the end
of a Bash function," Red Hat reports. So rather than spitting out "Vulnerable,"
a protected version of Bash will spit out the following when you run the
aforementioned command:
$ 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
--
Cowboy
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