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Comment by claudius | Hacker News Reader

The second test there

  env X='() { (a)=>\' sh -c "echo date"; cat echo

calls sh rather than bash, which is likely not linked to bash on Debian-y systems.

Furthermore, keep in mind http://thejh.net/misc/website-terminal-copy-paste and use C-x C-e.

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Pales in comparison to

    curl https://shellshocker.net/fixbash | sh

Are you vulnerable to giving attackers shell access on your computers? Pipe this into your shell and find out!

OK so I'm not the only person deeply troubled by their generous offer to remotely test my servers for vulnerability. Thank god they included the safe 'at-home' test kit

Not only that, but it's going to ask for your sudo password too. No reason to be leary of that ;-)

Also...

Are you in doubt if your server is vulnerable? just create this simple bash CGI file, and then get it called by us!

Just in case your apache did not have any bash CGI as usual :)

Good grief.

What could possibly go wrong.

(I had a rubber stamp made up with this saying. It is part of my black bag.)

If it's not bash it shouldn't run that. It's not about detecting bash, but the vulnerability.

But if your login shell isn't bash, and the test itself doesn't run bash, at what point are you actually testing bash (the software that is known to have at least once contained this vulnerability)?

It doesn't matter. If you find another shell that is vulnerable it's still a problem. Apparently it's only bash though.

sh will run whatever is pointed by the symlink. It's a good idea to try that than relying on bash being in its place and that an attacher hasn't masked it. Apache and other daemons will run sh, so that's what you want to try.

If you have bash installed, but it isn't the system bash (/bin/sh), and none of your scripts explicitly call bash or have a bash shebang, then you aren't vulnerable. However, if bash is your /bin/sh, then even a script that appears to have nothing to do with bash but happens to call something like system() will invoke bash.

But that line was intended to test whether your installed version of Bash is vulnerable to this attack. You don’t do that by solely calling /bin/sh.

Of course, you can also check /bin/sh explicitly if you are worried about extra copies of Bash hiding there.

If the test works, you are using bash and it's still vulnerable. That's all you need to know. By changing the call you make the test less effective for the reasons explained above.

it could be a bug in the sh compatibility mode

okay, let me make this little table. "VULN" denotes the test above (with sh rather than bash) detecting a vulnerable situation, "OK" means the test detects no vulnerability.

  sh → bash | bash vulnerable | VULN
  sh → bash | bash fixed      | OK
  sh → dash | bash vulnerable | OK
  sh → dash | bash fixed      | OK

Why do you want to only test the first but not the third case? You can perfectly well have /bin/sh linked to dash and still be vulnerable, because e.g. dhclient calls a Bash script.

It's not that you shouldn't test other things, but as one single test this was much better than calling directly to bash.

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