The change is a small one, but it prevents dangerous attacks that previously worked on most supported version of Windows. The technique that Microsoft fixed on Tuesday was demonstrated by a researcher at this year s CanSecWest conference. The two main exploit mitigations in Windows now are ASLR (Address Space Layout Randomization) and DEP (Data Execution Prevention) They re meant to defeat memory corruption attacks in most cases, and techniques that can bypass both are relatively rare and valuable.
Source: https://threatpost.com/microsoft-fixes-aslrdep-bypass-bug/101983/