Note that this is not just limited to SharePoint. It impacts anything running ASP.NET except for 1.1 SP3.
Out of Band Release to Address Microsoft Security Advisory 2416728
This security update is rated Important for all supported editions of ASP.NET except Microsoft .NET Framework 1.0 Service Pack 3.
See here for versions and details: http://www.microsoft.com/technet/security/bulletin/MS10-070.mspx
SharePoint developers and server administrators need to follow up on this Microsoft Security Advisory.
Read this ASAP!
“This vulnerability affects Microsoft SharePoint 2010 and Microsoft SharePoint Foundation 2010. The vulnerability is in ASP.NET. We recommend that all SharePoint 2010 customers apply the workaround as soon as possible”