Published: 27 September 2014
GNU Bash through 4.3 bash43-026 does not properly parse function definitions in the values of environment variables, which allows remote attackers to execute arbitrary code or cause a denial of service (uninitialized memory access, and untrusted-pointer read and write operations) via a crafted environment, as demonstrated by vectors involving the ForceCommand feature in OpenSSH sshd, the mod_cgi and mod_cgid modules in the Apache HTTP Server, scripts executed by unspecified DHCP clients, and other situations in which setting the environment occurs across a privilege boundary from Bash execution. NOTE: this vulnerability exists because of an incomplete fix for CVE-2014-6271 and CVE-2014-7169.
this issue is mitigated by Florian Weimer's prefix-suffix patch that is included in https://ubuntu.com/security/notices/USN-2364-1 since bash parser vulnerabilities are now limited to specially named environment variables, and as such are no longer directly exposed to CGI scripts, SSH, etc. Once an upstream patch is made available, we will release bash updates, but we don't consider this to be a critical issue requiring immediate attention.