CVE-2014-6271

GNU Bash through version 4.3 improperly processes trailing strings that follow function definitions inside environment variable values, allowing injected commands to run (CWE-78, OS command injection); this flaw is widely known as 'Shellshock'. An attacker triggers it by supplying a crafted environment variable to any service that invokes Bash, most notably CGI web handlers but also SSH, DHCP clients, and other software that sets variables and spawns the shell. Successful exploitation yields arbitrary code execution with the privileges of the Bash process on the target host. Any Linux, Unix, or similar system running an unpatched Bash through 4.3 is affected, including web servers, appliances, and embedded devices that ship the shell. Exploitation is confirmed in the wild: the flaw is in CISA's KEV (added 2022-01-28) with a required action to apply vendor updates, and EPSS assigns it a 100% probability of exploitation within 30 days, so patching is urgent.

What to do: Apply Bash updates per your OS vendor's instructions, as required by the CISA KEV listing, ensuring the installed shell is a patched build newer than the unpatched 4.3-era code. Prioritize internet-exposed systems that pass environment variables to Bash, especially CGI-based web servers, and audit embedded appliances and other Linux/Unix hosts that may have been missed by standard patching.