This indicates an attack attempt to exploit a Cross Domain Policy Bypass vulnerability in Adobe Flash Player.
The vulnerability is due to insufficient sanitizing of cross domain policy in the application. A remote attacker can exploit this to bypass cross domain policy and upload arbitrary files onto vulnerability system.
Adobe Flash Player 22.214.171.1245 and earlier versions
Adobe Flash Player 126.96.36.1999 and earlier 13.x versions
Adobe Flash Player 188.8.131.522 and earlier 11.x versions
Security Bypass: Remote attackers can bypass security checks of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.