Hi,
Unfortunately, we currently do not have document of the default permissions for IIS7.0. But the default permissions for IIS7.0 is similar to the IIS6.0’s. With IIS7.0, the IIS_IUSRS built-in group replaces the IIS_WPG group and the IUSR built-in account replaces the IUSR_MachineName account.
Below are the articles about IIS6.0 default permissions and IIS7.0 built-in account changes:
Default permissions and user rights for IIS 6.0
http://support.microsoft.com/kb/812614
Understanding the Built-In User and Group Accounts in IIS 7.0
http://learn.iis.net/page.aspx/140/understanding-the-built-in-user-and-group-accounts-in-iis-70/
I hope this information helpful for you.