XCLN: Able to Log On with Incorrect Windows NT Credentials

CAUSE

The behavior described above will only occur if all of the following conditions are met:

• You physically log on to the Windows NT domain at the Exchange Server computer where your mailbox resides.
• The account with which you log on to the domain is the Primary Windows NT account of the mailbox being accessed.
• The ncalrpc protocol, which refers to the Local RPC protocol, is listed in the RPC_Binding_Order value of the following Registry key:

        HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Exchange\Exchange Provider

• The Exchange Windows client uses Local RPC communication to resolve the connection to the Exchange Server computer.

For example, you log on to the Exchange Server computer and create a profile with the Use Network Security During Logon option disabled. When attempting to log on to your mailbox, you are prompted to enter the appropriate Windows NT credentials. Even if you enter the wrong user name, domain name, or password, you will still be connected to your mailbox. This is because, like the Named Pipes protocol, Local RPC caches your logon credentials. These credentials override any credentials entered manually by you. This behavior is by design.

It is important to note that users will not be able to access another user's mailbox. If an attempt is made to do so with invalid Windows NT credentials, the user will be denied access to the mailbox, as expected. Also, local RPC communication is only used when Exchange Client is running on the same computer as the RPC target (in this case the server).