This script is Copyright (C) 2004-2013 Tenable Network Security, Inc.
The remote FreeBSD host is missing a security-related update.
According to the SpamAssassin 2.64 release announcement :
Security fix prevents a denial of service attack open to certain
malformed messages; this DoS affects all SpamAssassin 2.5x and 2.6x
versions to date.
The issue appears to be triggered by overly long message headers.
See also :
Update the affected package.
Risk factor :
Medium / CVSS Base Score : 5.0
CVSS Temporal Score : 3.7
Public Exploit Available : false