Posted by Lee on May 01

crypto isakmp aggressive-mode disable
should be the counter-measure.

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/security/a1/sec-a1-cr-book/sec-cr-c4.html#wp7822516900
To block all Internet Security Association and Key Management
Protocol (ISAKMP)
aggressive mode requests to and from a device, use the
crypto isakmp aggressive-mode disable
command in global configuration mode.

Regards,
Lee