Use-after-free vulnerability in the ByteArray class in the ActionScript 3 (AS3) implementation in Adobe Flash Player 13.x through 13.0.0.296 and 14.x through 18.0.0.194 on Windows and OS X and 11.x through 11.2.202.468 on Linux allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption) via crafted Flash content that overrides a valueOf function, as exploited in the wild in July 2015.

Adobe Security Bulletin APSB15-14 for Adobe Flash Player describes a flaw that can possibly lead to code execution when Flash Player is used to play a specially crafted SWF file.

Quoting from the APSB15-14:

Adobe has released security updates for Adobe Flash Player for Windows, Macintosh and Linux. These updates address a critical vulnerability (CVE-2015-3113) that could potentially allow an attacker to take control of the affected system.

Adobe is aware of reports that CVE-2015-3113 is being actively exploited in the wild via limited, targeted attacks. Systems running Internet Explorer for Windows 7 and below, as well as Firefox on Windows XP, are known targets.

External References:

https://helpx.adobe.com/security/products/flash-player/apsb15-14.html