A Bash vulnerability has just been announced, rated 10 on a scale of 10. The vulnerability is Network Exploitable. Patch Now.

GNU Bash through 4.3 incorrectly handle trailing strings after function definitions in the values of environment variables. An attacker could use this issue to bypass environment restrictions, such as SSH forced command environments, and execute arbitrary code.

You need to patch your systems now.

Update: If you already patched your system. Check it again. You may have to patch again due to a previous incomplete fixes. See CVE-2014-7169, Incomplete fix for CVE-2014-6271