# !epthook (hidden hook with EPT - stealth breakpoints)

### Command

> !epthook

### Syntax

> !epthook \[Address (hex)] \[pid ProcessId (hex)] \[core CoreId (hex)] \[imm IsImmediate (yesno)] \[buffer PreAllocatedBuffer (hex)] \[script { Script (string) }] \[asm condition { Condition (assembly/hex) }] \[asm code { Code (assembly/hex) }] \[output {OutputName (string)}]

### Description

Puts a hidden breakpoint (0xcc) on the target function in user-mode and kernel-mode without modifying the content of memory in the case of reading/writing.

{% hint style="info" %}
This implementation of the hidden hook causes vm-exit when it triggers. A faster implementation of EPT hidden hooks is [!epthook2](https://docs.hyperdbg.org/commands/extension-commands/epthook2), which is without vm-exits. Still, it has some limitations, as described in the documentation.
{% endhint %}

{% hint style="danger" %}
If you want to keep the current context without continuing the debuggee, you should use the '[bp](https://docs.hyperdbg.org/commands/debugging-commands/bp)' command instead.
{% endhint %}

### Parameters

**\[Address (hex)]**

The **Virtual** address of where we want to put the hook.

**\[pid ProcessId (hex)] (optional)**

Optional value to trigger the event in just a specific process. Add `pid xx` to your command; thus, the command will be executed if the process id is equal to `xx`. If you don't specify this option, then by default, you receive events on all processes.

Still, in the case of user-mode debugging, HyperDbg will apply it only to the current active debugging process (not all the processes). In that case, you can specify `pid all` to intercept events from the entire system.

**\[core CoreId (hex)] (optional)**

Optional value to trigger the event in just a specific core. Add `core xx` to your command thus command will be executed if core id is equal to `xx`. If you don't specify this option, then by default, you receive events on all cores.

**\[imm IsImmediate (yesno)] (optional)**

Optional value in which `yes` means the results (printed texts in scripts) should be delivered immediately to the debugger. `no` means that the results can be accumulated and delivered as a couple of messages when the buffer is full; thus, it's substantially faster, but it's not real-time. By default, this value is set to `yes`.

**\[buffer PreAllocatedBuffer (hex)] (optional)**

Optional value which reserves a safe [pre-allocated buffer](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action#pre-allocated-buffers) to be accessed within the event codes.

**\[script { Script (string) }] (optional)**

A HyperDbg [script](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action#script) will be executed each time the event is triggered.

**\[asm condition { Condition (assembly/hex) }] (optional)**

Optional assembly codes which check for [conditions](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-a-condition) in assembly.

**\[asm code { Code (assembly/hex) }] (optional)**

Optional [assembly codes](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action#custom-codes) will be executed each time the event is triggered.

**\[output {OutputName (string)}] (optional)**

Optional output resource name for [forwarding events](https://docs.hyperdbg.org/tips-and-tricks/misc/event-forwarding).

### Context

As the **Context** (`$context` pseudo-register in the event's script, `r8` in custom code, and `rdx` in condition code register) to the event trigger, **HyperDbg** sends the **virtual address** of where put the hidden hook's breakpoint.

### Short-circuiting

This event does not support **'**[**event short-circuiting**](https://docs.hyperdbg.org/tips-and-tricks/misc/event-short-circuiting)', as this mechanism won't make sense for the function hooks. If you want to change the execution path (e.g., ignoring a function call), you can directly manipulate the **RIP** register.

<pre class="language-clike"><code class="lang-clike">!epthook nt!ExAllocatePoolWithTag script {
<strong>    @rip = poi(@rsp); // return to the stack
</strong>    @rsp = @rsp + 8; // pop from the stack
<strong>    printf("ignoring calls to the target function\n");
</strong>}
</code></pre>

### Calling Stages

This event does not support [calling stages](https://docs.hyperdbg.org/tips-and-tricks/misc/event-short-circuiting). Due to the nature of function hooking implementing calling stages in this context wouldn't be meaningful.

### Debugger

This event supports three debugging mechanisms.

* Break
* Script
* Custom Code

{% hint style="info" %}
Please read "[How to create a condition?](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-a-condition)" if you need a conditional event, a conditional event can be used in all "**Break**", "**Script**", and "**Custom Code**".
{% endhint %}

#### Break

Imagine we want to put a hook on ``fffff800`4ed6f010``, this will break into the debugger when the target address hits and gives the control back to you.

```c
HyperDbg> !epthook fffff800`4ed6f010
```

Alternatively, you can use `nt!ExAllocatePoolWithTag` too.

```c
HyperDbg> !epthook nt!ExAllocatePoolWithTag
```

You can also use an expression like `nt!ExAllocatePoolWithTag+@rcx+5` too.

```c
HyperDbg> !epthook nt!ExAllocatePoolWithTag+@rcx+5
```

#### Script

Using the following command, you can use HyperDbg's Script Engine. You should replace the string between braces (`HyperDbg Script Here`) with your script. You can find script examples [here](https://docs.hyperdbg.org/commands/scripting-language/examples).

```
HyperDbg> !epthook fffff800`4ed6f010 script { HyperDbg Script Here }
```

The above command when messages don't need to be delivered immediately.

```
HyperDbg> !epthook fffff800`4ed6f010 script { HyperDbg Script Here } imm no
```

**Script (From File)**

If you saved your script into a file, then you can add `file:` instead of a script and append the file path to it. For example, the following examples show how you can run a script from `file:c:\users\sina\desktop\script.txt`.

```
HyperDbg> !epthook fffff800`4ed6f010 script {file:c:\users\sina\desktop\script.txt}
```

{% hint style="success" %}
You can use [**event forwarding**](https://docs.hyperdbg.org/tips-and-tricks/misc/event-forwarding) to forward the event monitoring results from this event and other events to an external source, e.g., **File**, **NamedPipe**, or **TCP Socket**. This way, you can use **HyperDbg** as a monitoring tool and gather your target system's behavior and use it later or analyze it on other systems.
{% endhint %}

### Custom Code

Please read "[How to create an action?](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action)" to get an idea about running a custom buffer code in **HyperDbg**.

{% hint style="warning" %}
Your custom code will be executed in vmx-root mode. Take a look at [this topic](https://docs.hyperdbg.org/tips-and-tricks/considerations/vmx-root-mode-vs-vmx-non-root-mode) for more information. Running code in vmx-root is considered "[unsafe](https://docs.hyperdbg.org/tips-and-tricks/considerations/the-unsafe-behavior)".
{% endhint %}

**Run Custom Code (Unconditional)**

Putting a hook on `fffff801deadbeef` and run 3 nops whenever the hook is triggered. Take a look at [Run Custom Code](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action#run-custom-codes) for more information.

```c
HyperDbg> !epthook fffff801deadbeef code {90 90 90}
```

Or if you want to use assembly codes directly, you can add an `asm` before the `code`.

```clike
HyperDbg> !epthook fffff801deadbeef asm code {nop; nop; nop}
```

**Run Custom Code (Conditional)**

Putting a hook on `fffff801deadbeef` and run 3 nops whenever the hook is triggered and also 3 nops condition. Take a look at [Run Custom Code](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-an-action#run-custom-codes) and [how to create a condition](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/how-to-create-a-condition) for more information.

```c
HyperDbg> !epthook fffff801deadbeef code {90 90 90} condition {90 90 90}
```

Or if you want to use assembly codes directly, you can add an `asm` before the `condition` and also before the `code`.

```clike
HyperDbg> !epthook fffff801deadbeef asm code {nop; nop; nop} asm condition {nop; nop; nop}
```

{% hint style="success" %}
Keep in mind that a conditional event can be used in **Breaking to Debugger** and **Running Script** too.
{% endhint %}

### IOCTL

This command uses the same method to [send IOCTL for regular events](https://docs.hyperdbg.org/using-hyperdbg/sdk/ioctl/event-registration).

Use `HIDDEN_HOOK_EXEC_CC` as **EventType**, and send the address of where you want to hook in `OptionalParam1`in `DEBUGGER_GENERAL_EVENT_DETAIL`.

### Design

Take a look at "[Design of !epthook](https://docs.hyperdbg.org/design/features/vmm-module/design-of-epthook)" to see how does it work.

### Remarks

This command is much slower than **!epthook2**, because it causes vm-exits, but on the other hand, this implementation doesn't have any limitation. For example, you can use this command for hooking user-mode while you can't use **!epthook2** on user-mode.

{% hint style="danger" %}
You shouldn't use any of **!monitor**, **!epthook**, and **!epthook2** commands on the same page (4KB) simultaneously. For example, when you put a hidden hook (**!epthook2**) on **0x10000005**, you shouldn't use any of **!monitor** or **!epthook** commands on the address starting from **0x10000000** to **0x10000fff**.

You can use **!epthook** (just ***!epthook*** not **!epthook2** and not **!monitor**) on two or more addresses on the same page (means that you can use the **!epthook** multiple times for addresses between a single page or putting multiple hidden breakpoints on a single page). But you can't use **!monitor** or **!epthook2** twice on the same page.
{% endhint %}

This command creates an [event](https://docs.hyperdbg.org/design/debugger-internals/events). Starting from HyperDbg **v0.7**, events are guaranteed to keep the debuggee in a halt state (in the [Debugger Mode](https://docs.hyperdbg.org/using-hyperdbg/prerequisites/operation-modes#debugger-mode)); thus, nothing will change during its execution and the context (registers and memory) remain untouched. You can visit [instant events](https://docs.hyperdbg.org/tips-and-tricks/misc/instant-events) for more information.

### Requirements

Post-Nehalem Processor (EPT)

Processor with Execute-only Pages Support

### Related

[bp (set breakpoint)](https://docs.hyperdbg.org/commands/debugging-commands/bp)

[!epthook2 (hidden hook with EPT - detours)](https://docs.hyperdbg.org/commands/extension-commands/epthook2)


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