A few hours ago we released a Microsoft Security Advisory about a security vulnerability in ASP.NET. This vulnerability exists in all versions of ASP.NET.
This vulnerability was publically disclosed late Friday at a security conference. We recommend that all customers immediately apply a workaround (described below) to prevent attackers from using this vulnerability against your ASP.NET applications.
What does the vulnerability enable?
An attacker using this vulnerability can request and download files within an ASP.NET Application like the web.config file (which often contains sensitive data).
At attacker exploiting this vulnerability can also decrypt data sent to the client in an encrypted state (like ViewState data within a page).