This indicates an attack attempt to exploit a Security Bypass vulnerability in Adobe Flash Player.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted HTTP Request. A remote attacker may be able to exploit this to security mechanism of the application via a crafted HTTP request.
Adobe Flash Player Desktop Runtime 188.8.131.52 and earlier on Windows and Macintosh
Adobe Flash Player for Google Chrome 184.108.40.206 and earlier on Windows, Macintosh and Linux
Adobe Flash Player for Microsoft Edge and Internet Explorer 11 220.127.116.11 and earlier
Adobe Flash Player for Linux 18.104.22.1686 and earlier on Linux
AIR Desktop Runtime 22.214.171.124 and earlier on Windows and Macintosh
AIR SDK 126.96.36.199 and earlier on Windows, Macintosh, Android and iOS
AIR SDK & Compiler 188.8.131.52 and earlier on Windows, Macintosh, Android and iOS
Security Bypass: Remote attackers can bypass security mechanism of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.