Securing SharePoint’s People Picker for Extranet use
About People Picker
One of the often used features of SharePoint (WSS 3.0 and MOSS 2007) is People Picker. This is the component responsible for providing a fancy user interface for finding users when provisioning access:
By default, which in this context means - “I did a full installation of MOSS 2007 with mostly default settings and didn’t pay particular attention to securing anything” – People Picker is not secure.
Main issue with People Picker is that it’s accessible for regular users of a given site. Thus by accessing /_layouts/aclinv.aspx">http://<portal>/_layouts/aclinv.aspx anyone with basic access to the site can list and view existing users of the system:
By typing 'a' as the user and hitting search one can review a list of accounts that match this search term. Obviously this isn't a big issue in intranets and similar closed systems where trust is already given for that particular user performing the search. For anonymous sites (public WCM-sites mostly) lockdown mode should resolve most issues related to /_layouts/ application pages. See this article for more details: http://technet.microsoft.com/en-us/library/cc263468.aspx#section6.
What additional approaches can you take to secure People Picker?
Modifying People Picker behavior with stsadm.exe
Stsadm.exe (with SP1) enables you to control People Picker with the following properties:
These are well documented here: http://technet.microsoft.com/en-us/library/cc263318.aspx.
Deny access to /_layouts/aclinv.aspx
It would also be a good idea to deny access to /_layouts/aclinv.aspx. For some reason SharePoint doesn't have a built-in security authorization for this given application page like it has for settings.aspx. A proper approach would be to filter access to this given application page on the border firewall.
Alternatively, brewing your own HTTP Handler to filter out requests is also a viable option. See this article for more details: http://msdn.microsoft.com/en-us/library/bb457204.aspx
You should know that modifying anything underneath /_layouts/ probably breaks any support, so proceed with caution.
Modifying aclinv.aspx has its advantages too. This is the control from aclinv.aspx that renders People Picker:
Several properties exist that can help in securing People Picker functionality:
- ValidatorEnabled [true, false]: Set to false to disable validation of user accounts
- Rows [#]: Set to 1 to prevent multiple user access
- ShowButtons [true, false]: Set to false to disable the two functional buttons (check names and addressbook)
- ValidateResolvedEntity [true, false]: Set to false to prevent validation of resolved entity
- UrlZone [Custom, Intranet, Extranet, Internet, Default]: Specify with zone (AAM) to use for this control. Might be handy to set this to Intranet only
Hope this helps :)