Ars reports that a new bug has been found in GNU Bash allows remote attackers to execute arbitrary code by setting the process trailing strings after function definitions in the values of environment variables.
This bug is reported to be present in RHEL (ver 4 through 7), Fedora, CentOS (ver 5 through 7), Ubuntu (ver 10.04 LTS, 12.04 LTS, and 14.04 LTS), Debian, and even OS X Mavericks.
This bug is exploitable through Apache servers with mod_cgi and mod_cgid loaded, OpenSSH, malicious DHCP servers in a compromised wireless access point through dhclient, as well as the CUPS printing system.
The Ars also includes a simple single liner that will test your setup for the newly found discovery:
env x='() { :;}; echo vulnerable' bash -c "echo this is a test"
A vulnerable system will output the following:
vulnerable
this is a test
While a patched or unaffected system outputs:
bash: warning: x: ignoring function definition attempt
bash: error importing function definition for `x'
this is a test
A patch is already out, so administrators are advised to update Bash.
Editor's Update: Security Engineer Tavis Ormandy has said "The bash patch seems incomplete to me, function parsing is still brittle".
$ env X='() { (a)=>\' sh -c "echo date"; cat echo
(Score: 2) by fnj on Friday September 26 2014, @09:39AM
We'll quit dissing no-account cowards when the lazy bums get off their ass and sign up for an account, and then put their fragile egos on the line by making signed posts.
P.S., I do read cowards because I don't want to hide safely behind mommy's apron. But I will never quit making fun of the sniveling lightweights.