As a cumulative update, 4.0.3 rolled up numerous "hotfixes." It addressed common issues in:
In the long history of the .NET ecosystem, version 4.0.3 is often overlooked. Sandwiched between the revolutionary .NET 4.0 and the feature-rich 4.5, version 4.0.3 wasn't a flashy release. It didn't bring new languages or radical API changes. Instead, it represented the "plumbing" work that keeps the software world running. .net framework 4.0.3