IPC$ share and null session behavior in Windows

Applies to: Windows Server 2008 R2 DatacenterWindows Server 2008 R2 EnterpriseWindows Server 2008 R2 Standard

This article describes the inter-process communication share (IPC$) and null session behavior in Windows 7, Windows Server 2008 R2, Windows Vista, Windows Server 2008, Windows XP, and Windows Server 2003.

About IPC$ share

The IPC$ share is also known as a null session connection. By using this session, Windows lets anonymous users perform certain activities, such as enumerating the names of domain accounts and network shares.

The IPC$ share is created by the Windows Server service. This special share exists to allow for subsequent named pipe connections to the server. The server's named pipes are created by built-in operating system components and by any applications or services that are installed on the system. When the named pipe is being created, the process specifies the security that is associated with the pipe, and then makes sure that access is only granted to the specified users or groups.

Configure anonymous access by using network access policy settings in Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2

In Windows Server 2003, Windows Server 2008, or Windows Server 2008 R2, the IPC$ share cannot be managed or restricted. However, an administrator has controls over any named pipes that were enabled so that they can be accessed anonymously by using the Network access: Named Pipes that can be accessed anonymously security policy setting. If the policy setting is configured to have no entries (such as a Null value), no named pipes can be accessed anonymously, and you have to make sure that no applications or services in the environment rely on anonymous access to any named pipes on the server.

Although Windows Server 2003 no longer prevents anonymous access to IPC$ share, there is a Network access: Let Everyone permissions apply to anonymous users security policy setting that defines whether the Everyone group is added to an anonymous session. If this setting is disabled, the only resources that can be accessed by an anonymous user are those that are specifically granted to the Anonymous Logon group.

Additionally, in Windows Server 2012 or a later Windows Server-based operating system, there is a feature to determine whether anonymous sessions should be enabled on file servers. It is determined by checking if any pipes or shares are marked for remote access.