Ubuntu Security Notice USN-705-1 – It was discovered that NTP did not properly perform signature verification. A remote attacker could exploit this to bypass certificate validation via a malformed SSL/TLS signature.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/73683/USN-705-1.txt
Source: https://packetstormsecurity.com/files/73683/Ubuntu-Security-Notice-705-1.html