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{% endhint %}
## Introduction
Handles in a process allow to **access** different **Windows resources**:
.png>)
There have been already several **privilege escalation** cases where a **privileged process** with **open and inheritable handles** have **run** an **unprivileged process** giving it **access to all those handles**.
For example, imagine that **a process running as SYSTEM open a new process** (`OpenProcess()`) with **full access**. The same process **also creates a new process** (`CreateProcess()`) **with low privileges but inheriting all the open handles of the main process**.\
Then, if you have **full access to the low privileged process**, you can grab the **open handle to the privileged process created** with `OpenProcess()` and **inject a shellcode**.
## **Interesting Handles**
### **Process**
As you read on the initial example if an **unprivileged process inherits a process handle** of a **privileged process** with enough permissions it will be able to execute **arbitrary code on it**.
In [**this excellent article**](http://dronesec.pw/blog/2019/08/22/exploiting-leaked-process-and-thread-handles/) you can see how to exploit any process handle that has any of the following permissions:
* PROCESS\_ALL\_ACCESS
* PROCESS\_CREATE\_PROCESS
* PROCESS\_CREATE\_THREAD
* PROCESS\_DUP\_HANDLE
* PROCESS\_VM\_WRITE
### Thread
Similar to the process handles, if an **unprivileged process inherits a thread handle** of a **privileged process** with enough permissions it will be able to execute **arbitrary code on it**.
In [**this excellent article**](http://dronesec.pw/blog/2019/08/22/exploiting-leaked-process-and-thread-handles/) you can also see how to exploit any process handle that has any of the following permissions:
* THREAD\_ALL\_ACCESS
* THREAD\_DIRECT\_IMPERSONATION
* THREAD\_SET\_CONTEXT
### File, Key & Section Handles
If an **unprivileged process inherits** a **handle** with **write** equivalent **permissions** over a **privileged file or registry**, it will be able to **overwrite** the file/registry (and with a lot of **luck**, **escalate privileged**).
**Section Handles** are similar to file handles, the common name of this kinds of [objects is **"File Mapping"**](https://docs.microsoft.com/en-us/windows/win32/memory/file-mapping). They are used to work with **big files without keeping the entire** file in memory. That makes the exploitation kind of "similar" to the exploitation of a File Handle.
## How to see handles of processes
### Process Hacker
[**Process Hacker**](https://github.com/processhacker/processhacker) is a tool you can download for free. It has several amazing options to inspect processes and one of them is the **capability to see the handles of each process**.
Note that in order to **see all the handles of all the processes, the SeDebugPrivilege is needed** (so you need to run Process Hacker as administrator).
To see the handles of a process, right click in the process and select Handles:
.png>)
You can then right click on the handle and **check the permissions**:
.png>)
### Sysinternals Handles
The [**Handles** ](https://docs.microsoft.com/en-us/sysinternals/downloads/handle)binary from Sysinternals will also list the handles per process in the console:
.png>)
### LeakedHandlesFinder
[**This tool**](https://github.com/lab52io/LeakedHandlesFinder) allows you to **monitor** leaked **handles** and even **autoexploit** them to escalate privileges.
### Methodology
Now that you know how to find handles of processes what you need to check is if any **unprivileged process is having access to privileged handles**. In that case, the user of the process could be able to obtain the handle and abuse it to escalate privileges.
{% hint style="warning" %}
It was mentioned before that you need the SeDebugPrivilege to access all the handles. But a **user can still access the handles of his processes**, so it might be useful if you want to privesc just from that user to **execute the tools with the user regular permissions**.
For example, the following code belongs to a **Windows service** that would be vulnerable. The vulnerable code of this service binary is located inside the **`Exploit`** function. This function is starts **creating a new handle process with full access**. Then, it's **creating a low privileged process** (by copying the low privileged token of _explorer.exe_) executing _C:\users\username\desktop\client.exe_. The **vulnerability resides in the fact it's creating the low privileged process with `bInheritHandles` as `TRUE`**.
Therefore, this low privileges process is able to grab the handle of the high privileged process crated first and inject and execute a shellcode (see next section).
In a real scenario you probably **won't be able to control the binary** that is going to be executed by the vulnerable code (_C:\users\username\desktop\client.exe_ in this case). Probably you will **compromise a process and you will need to look if you can access any vulnerable handle of any privileged process**.
{% endhint %}
In this example you can find the code of a possible exploit for _C:\users\username\desktop\client.exe_.\
The most interesting part of this code is located in `GetVulnProcHandle`. This function will **start fetching all the handles**, then it will **check if any of them belongs to the same PID** and if the handle belongs to a **process**. If all these requirements are completed (an accessible open process handle is found) , it try to **inject and execute a shellcode abusing the handle of the process**.\
The injection of the shellcode is done inside the **`Inject`** function and it will just **write the shellcode inside the privileged process and create a thread inside the same process** to execute the shellcode).
```c
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <wincrypt.h>
#include <psapi.h>
#include <tchar.h>
#include <tlhelp32.h>
#include "client.h"
#pragma comment (lib, "crypt32.lib")
#pragma comment (lib, "advapi32")
#pragma comment (lib, "kernel32")
int AESDecrypt(char * payload, unsigned int payload_len, char * key, size_t keylen) {
HCRYPTPROV hProv;
HCRYPTHASH hHash;
HCRYPTKEY hKey;
if (!CryptAcquireContextW(&hProv, NULL, NULL, PROV_RSA_AES, CRYPT_VERIFYCONTEXT)){
return -1;
}
if (!CryptCreateHash(hProv, CALG_SHA_256, 0, 0, &hHash)){
return -1;
}
if (!CryptHashData(hHash, (BYTE*)key, (DWORD)keylen, 0)){
return -1;
}
if (!CryptDeriveKey(hProv, CALG_AES_256, hHash, 0,&hKey)){
return -1;
}
if (!CryptDecrypt(hKey, (HCRYPTHASH) NULL, 0, 0, payload, &payload_len)){
// Inject and run the payload in the privileged context
Inject(hProc, payload, payload_len);
printf("done.\n");
}
getchar();
return 0;
}
```
### Exploit Example 2
{% hint style="info" %}
In a real scenario you probably **won't be able to control the binary** that is going to be executed by the vulnerable code (_C:\users\username\desktop\client.exe_ in this case). Probably you will **compromise a process and you will need to look if you can access any vulnerable handle of any privileged process**.
{% endhint %}
In this example, **instead of abusing the open handle to inject** and execute a shellcode, it's going to be **used the token of the privileged open handle process to create a new one**. This is done in lines from 138 to 148.
Note how the **function `UpdateProcThreadAttribute`** is used with the **attribute `PROC_THREAD_ATTRIBUTE_PARENT_PROCESS` and the handle to the open privileged process**. This means that the **created process thread executing \_cmd.exe**\_\*\* will have the same token privilege as the open handle process\*\*.
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