October 2014 – “Shellshock” Vulnerability

October 2014 – “Shellshock” Vulnerability

From the US-CERT Release:

Systems Affected

  • GNU Bash through 4.3.
  • Linux and Mac OS X systems, on which Bash is part of the base operating system.
  • Any BSD or UNIX system on which GNU Bash has been installed as an add-on.
  • Any UNIX-like operating system on which the /bin/sh interface is implemented as GNU Bash.


A critical vulnerability has been reported in the GNU Bourne-Again Shell (Bash), the common command-line shell used in many Linux/UNIX operating systems and Apple’s Mac OS X. The flaw could allow an attacker to remotely execute shell commands by attaching malicious code in environment variables used by the operating system. The United States Department of Homeland Security (DHS) is releasing this Technical Alert to provide further information about the GNU Bash vulnerability.


GNU Bash versions 1.14 through 4.3 contain a flaw that processes commands placed after function definitions in the added environment variable, allowing remote attackers to execute arbitrary code via a crafted environment which enables network-based exploitation.

Critical instances where the vulnerability may be exposed include:

  • Apache HTTP Server using mod_cgi or mod_cgid scripts either written in bash, or spawn GNU Bash subshells, or on any system where the /bin/sh interface is implemented using GNU Bash.
  • Override or Bypass ForceCommand feature in OpenSSH sshd and limited protection for some Git and Subversion deployments used to restrict shells and allows arbitrary command execution capabilities. This data path is vulnerable on systems where the /bin/sh interface is implemented using GNU Bash.
  • Allow arbitrary commands to run on a DHCP client machine.


The Survalent SCADA Server (and Client WorldStation) run on Microsoft Windows and are not subject to this vulnerability.