Ubuntu Security Notice 511-2 – USN-511-1 fixed vulnerabilities in krb5 and librpcsecgss. The fixes were incomplete, and only reduced the scope of the vulnerability, without fully solving it. It was discovered that the libraries handling RPCSEC_GSS did not correctly validate the size of certain packet structures. An unauthenticated remote user could send a specially crafted request and execute arbitrary code with root privileges.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/59175/USN-511-2.txt
Source: https://packetstormsecurity.com/files/59175/Ubuntu-Security-Notice-511-2.html