A security feature bypass vulnerability exists when Lync for Mac 2011 fails to properly sanitize specially crafted messages. An attacker who successfully exploited this vulnerability could cause a targeted Lync for Mac 2011 user's system to browse to an attacker-specified website or automatically download file types on the operating system's safe file type list.
For an attacker to exploit the vulnerability, a specially crafted message needs to be sent to a targeted user. The targeted user does not need to take any actions after receiving the message.
Microsoft is not planning on fixing this vulnerability in Microsoft Lync for Mac 2011. Microsoft recommends upgrading to Skype for Business on Mac.