A security flaw was found in bash, which could be exploited remotely via applications which parse untrusted user scripts via bash. This flaw is different from CVE-2014-6277, CVE-2014-7169 and CVE-2014-7186.

Bash before 4.4 allows local users to execute arbitrary commands with root privileges via crafted SHELLOPTS and PS4 environment variables.

A heap-based buffer overflow exists in GNU Bash before 4.3 when wide characters, not supported by the current locale set in the LCCTYPE environment variable, are printed through the echo built-in function. A local attacker, who can provide data to print through the "echo -e" built-in function, may use this flaw to crash a script or execute code with the privileges of the bash process. This occurs because ansicstr() in lib/sh/strtrans.c mishandles u32cconv().

A vulnerability was found in a way bash expands the $HOSTNAME. Injecting the hostname with malicious code would cause it to run each time bash expanded \h in the prompt string.

References:

http://seclists.org/oss-sec/2016/q3/528

Ubuntu bug:

https://bugs.launchpad.net/ubuntu/+source/bash/+bug/1507025