This indicates an attack attempt to exploit an Information Disclosure vulnerability in Adobe Flash Player.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted MP4 file. An attacker can exploit this by tricking an unsuspecting user into visiting a malicious webpage, and obtain information on the targeted user's system.
Adobe Flash Player Desktop Runtime 126.96.36.199 and earlier on Windows and Macintosh
Adobe Flash Player Extended Support Release 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 on Windows 10
Adobe Flash Player for Internet Explorer 10 and 11 18.104.22.168 and earlier on Windows 8.0 and 8.1
Adobe Flash Player for Linux 22.214.171.1248 and earlier on Linux
AIR Desktop Runtime 126.96.36.199 and earlier on Windows and Macintosh
AIR SDK 188.8.131.52 and earlier on Windows, Macintosh, Android and iOS
AIR SDK & Compiler 184.108.40.206 and earlier on Windows, Macintosh, Android and iOS
AIR for Android 220.127.116.11 and earlier
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.