This indicates an attack attempt against a Zero-Day vulnerability discovered by the FortiGuard Global Security Research Team. This signature should help mitigate the Zero-Day threat proactively - both prior to, and after an official fix is available from the vendor. Once this official fix is available, further details about our discovery will be made available in an advisory on our FortiGuard Center (http://www.fortiguard.com). This signature and description will also be updated at this point in time.
This is a Zero-Day (unpatched) vulnerability that has been discovered by the FortiGuard Global Security Research Team.
Any Zero-Day vulnerabilities can have a large impact due to the fact that they remain unpatched, making exploit attempts more effective since the given attack vector remains open.