Named Pipe Port Install Additional Drivers

Virtual serial ports can output to physical serial ports, files, or named pipes.

You can also use virtual ports to send debugging data from a virtual machine to the host system or to another virtual machine.

Named Pipe Port Install Additional Drivers

You do not need to install additional drivers in the virtual machine.

Either locate an existing output file or browse to a directory and type a filename to create a new output file.

If the serial port in the guest operating system is being used in polled mode rather than interrupt mode, you might notice performance issues.

This option forces the virtual machine to yield processor time if the only task it is trying to do is poll the virtual serial port.

Repeat this procedure for the second virtual machine, but set it up as the client by selecting This end is the client when you configure the named pipe.

For example, in a simple application a specific sequence of information could be exchanged between the server and the client (a handshake) before any actual data is exchanged.

Processes often talk to each other and many software packages contain multiple components which need to exchange data to run properly.

Named pipes are one of the many forms of IPC in use today and are extensively used on the Windows platform as a means to exchange data between running processes in a semi-persistent manner.

The NPFS is a hidden partition which functions just like any other; files are written, read and deleted using the same mechanisms as a standard Windows file system.

So named pipes are actually just files on a hard drive which persist until there are no remaining handles to the file, at which point the file is deleted by Windows.

For example, the Service Control Manager (SCM) of Windows was discovered to be vulnerable to race conditions related to Named Pipes in 2000, more recently, a predictable named pipe used by Google Chrome could be exploited to help escape from the browser sandbox.

This means that the user needs to know the name of the pipe before the vulnerable service is started and then wait for a client to connect.

Ideal targets are services which run at administrator or SYSTEM level privileges, for the obvious reasons.

If impersonation is allowed, the server can use the impersonation token to act on the clients behalf.

The client specifies a security quality of service (SQOS) when connecting to the server.

The level of impersonation provided to the server by the SQOS can be one of the following four flags, which in the case of named pipes are provided as part of the connection process when calling the CreateFile function.

From here it is just a matter of calling the CreateProcessAsUser() function to spawn a process (lets say cmd.exe) using the new primary token which has the security context of the client.

For example, the getsystem module in Metasploit makes use of named pipes to escalate to SYSTEM level privileges from Administrator.

The first one works by starting a named pipe server and then using administrator privileges to schedule a service to run as SYSTEM.

This service connects as a named pipe client to the recently created server.

Therefore, the most important element is to ensure that the named pipe server is indeed the correct server.

In other words, it can give an indication as to whether another process has already created a named pipe server with this name and can allow for corrective action.

This could be in the form of creating the server with an alternate name or stopping execution entirely.It is also a good idea that any intended clients are also made aware, if possible, that the server instance is not valid or has been changed so that they do not attempt to connect.

This is an approach the Google Chrome browser uses to help thwart unintended processes from creating the named pipe servers it uses for communication.

If the maximum number of potential clients which will connect is known, a hard figure should be set to ensure that no further clients can connect.

The flag which defines the maximum number of concurrent pipe instances is set as an integer value between 1 and 255 at invocation.

To allow unlimited connections, the flag is set to PIPEUNLIMITEDINSTANCES.

The easiest and most direct way to prevent a named pipe client from being impersonated is disallow pipe impersonation when connecting to a server.

This can be achieved by setting the SECURITYIDENTIFICATION flag or the SECURITYANONYMOUS flag when calling the CreateFile() function as part of the client connection process.