The security fix rectifies an unloading bug that can, under some circumstances, let ASP.NET applications misbehave and return the source code (.aspx) of the application or any other file in the web application directory. The Mono Project blog notes:

We strongly advise every Mono 2.8.xx user to upgrade to Mono 2.8.2 if they host web applications with it

The other changes are:

• Backport ParallelFx improvements from master (jlaval)
• Fix state check for short-circuiting with SupportRecursion in ReaderWriterLockSlim #655361 (jlaval)
• Increment Count even on single-processor in SpinWait. Fix #624849. (jlaval)
• Update ThreadLocal to use default(T) for initialization with parameterless ctor. Fix #658689. (jlaval)

Related article: Mono 2.8