Recently, a vulnerability was discovered in the shell program Bash which could allow a remote attacker to execute any code he likes on the remote server. It has a
CVSS severity of 10 on a scale from 1 to 10, so it is very serious. A vulnerable version of Bash is included with YubiRADIUS.
The problem is described in this link from NIST and references CVE-2014-6271 -
http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2014-6271. This link also contains links to external sites where you can manually download and apply patches to fix the vulnerability in the OS used in YubiRADIUS.
However, you can also upgrade to
GreenRADIUS - Yubico Edition, the next generation of YubiRADIUS. GreenRADIUS -Yubico Edition is a fully maintained open source RADIUS server built by the same team that developed YubiRADIUS. Due to severity of the latest vulnerabilities, Green Rocket Security,
a Yubico partner, is offering a free upgrade to GreenRADIUS - Yubico Edition, which has the Shellshock fixes applied and tested, a hardened virtual appliance, and many more fixes (e.g. for the serious Heartbleed SSL vulnerability). Find out more about GreenRADIUS - Yubico Edition
here.