The remote host is vulnerable to a Denial of Service (Dos) attack.
According to its banner, the version of Squid proxy caching server installed on the remote host is 2.x or 3.x earlier than 3.0.STABLE23 or 18.104.22.168. Such versions reportedly use incorrect data validation when processing specially crafted DNS packets. An attacker, exploiting this flaw, could cause a short term denial of service.
Either upgrade to Squid version 3.0.STABLE23 or 22.214.171.124 or later, or apply the patch referenced in the project's advisory above.