Snort log : Attempted User Privilege Gain

[Steve Williams]

PROTOCOL-DNS Microsoft SMTP excessive answer records buffer overflow attempt

Just Curious what this is and how to stop it in snort, I first thought someone was trying to get in but now I am not so sure as I changed my external IP and it happened straight away
on the new External IP. From what I can gather its something to do with a vunerability in dns but at a loss where to start, if its not an issue then fine but its happening a lot.