To determine if you have support for RPC over HTTP enabled on servers running Windows Server 2003, follow these steps:
- In Control Panel, click Add/Remove Programs
- Click Add/Remove Windows Components
This will start the Windows Components Wizard
- Click Networking Services, and then click
DCOM is a protocol that can be used on top of the RPC protocol by client / server applications. By default, a server running Windows Server that is configured to support RPC over HTTP will also accept DCOM requests using this protocol. These DCOM requests are then sent to a local port on the server implementing RPC over HTTP (TCP port 593).
Security best practices recommend disabling or removing all nonessential components and services.
If DCOM support is not required on your RPC over HTTP servers, you can remove DCOM support by modifying the registry. To use RPC over HTTP to remove DCOM support, follow these steps:WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
- Click Start, click Run, type Regedit.exe, and then click
- Locate the following registry entry:HKEY_LOCAL_MACHINE\Software\Microsoft\Rpc\RpcProxy
Note Entries in the "ValidPorts" REG_SZ string value are separated by a semicolon. By default, Windows Server 2003 has the following entry:<Local_server_name>:100-5000This entry allows RPC over HTTP to use ports 100-5000.
- Change the default entry that is listed in the note in step 2 to the following: <Local_server_name>:100-592;<Local_server_name>:594-5000
Doing this disables support for DCOM.
- Remove any entries or any other port ranges that explicitly contain “:593”. For example, remove the following entry: <servername>:593
- Remove any entries or any other port ranges that implicitly contain "593". For example, remove the following entry: <servername>:100-2000 and replace it with:<Local_server_name>:100-592;<Local_server_name>:594-2000.
When you use RPC over HTTP to remove DCOM support, you can help mitigate the vulnerabilities that are addressed in security bulletin MS03-026 for servers that expose RPC services over HTTP ports 80,443.
Article ID: 826382 - Last Review: Jun 16, 2009 - Revision: 1