!epthook (hidden hook with EPT - stealth breakpoints)
Description of the '!epthook' command in HyperDbg.
!epthook
!epthook [Address (hex)] [pid ProcessId (hex)] [core CoreId (hex)] [imm IsImmediate (yesno)] [buffer PreAllocatedBuffer (hex)] [script { Script (string) }] [condition { Condition (hex) }] [code { Code (hex) }]
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.
This implementation of the hidden hook causes vm-exit when it triggers. A faster implementation of EPT hidden hooks is !epthook2, which is without vm-exits. Still, it has some limitations, as described in the documentation.
If you want to keep the current context without continuing the debuggee, you should use the 'bp' command instead.
[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)
[script { Script (string) }] (optional)
[condition { Condition (hex) }] (optional)
[code { Code (hex) }] (optional)
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.This event does not support '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.
!epthook nt!ExAllocatePoolWithTag script {
@rip = poi(@rsp); // return to the stack
@rsp = @rsp + 8; // pop from the stack
printf("ignoring calls to the target function\n");
}
This event does not support calling stages. Due to the nature of function hooking implementing calling stages in this context wouldn't be meaningful.
This event supports three debugging mechanisms.
- Break
- Script
- Custom Code
Please read "How to create a condition?" if you need a conditional event, a conditional event can be used in all "Break", "Script", and "Custom Code".
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.HyperDbg> !epthook fffff800`4ed6f010
Alternatively, you can use
nt!ExAllocatePoolWithTag too.HyperDbg> !epthook nt!ExAllocatePoolWithTag
You can also use an expression like
nt!ExAllocatePoolWithTag+@rcx+5 too.HyperDbg> !epthook nt!ExAllocatePoolWithTag+@rcx+5
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.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}
You can use 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.
Please read "How to create an action?" to get an idea about running a custom buffer code in HyperDbg.
Your custom code will be executed in vmx-root mode. Take a look at this topic for more information. Running code in vmx-root is considered "unsafe".
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 for more information.HyperDbg> !epthook fffff801deadbeef code {90 90 90}
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 and how to create a condition for more information.HyperDbg> !epthook fffff801deadbeef code {90 90 90} condition {90 90 90}
Keep in mind that a conditional event can be used in Breaking to Debugger and Running Script too.
Use
HIDDEN_HOOK_EXEC_CC as EventType, and send the address of where you want to hook in OptionalParam1in DEBUGGER_GENERAL_EVENT_DETAIL.This command is much slower than !epthook2, because it cause 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.
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.
This is an event command, but in the current version of HyperDbg (in Debugger Mode), this command will continue the debuggee for some time; however, you can use this trick to make sure you won't lose any event.
Post-Nehalem Processor (EPT)
Processor with Execute-only Pages Support