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What is ntdll Hooking? ntdll.dll is a key system file in Windows that handles low-level functions like memory and system calls. ntdll hooking is when a program changes or intercepts these functions to control or monitor how they work. By doing this, the program can modify system behavior, hide its actions, or bypass security measures. This is often used in malware or debugging tools. So what are some ways of bypassing this ntdll hooks? Generally there are 4 ways of doing so : 1.Direct Syscalling 2.Indirect Syscalling 3.Ntdll Remapping 4.Blocking non-mirosoft dlls from loading in your process 1.Direct Syscalling Direct syscalling is a technique used to bypass hooks or other monitoring mechanisms by calling system functions directly, without going through the usual API layers like ntdll.dll. Normally, when programs need to interact with the operating system, they call functions in ntdll.dll, which then communicate with the kernel. However, if ntdll.dll functions are hooked or modified, these calls might be intercepted or altered. By direct syscalling, a program can skip over the hooked functions and directly invoke system calls in the kernel. This allows it to execute actions without being monitored or interfered with by the hook, providing a way to perform operations stealthily. 2.Indirect Syscalling Indirect syscall is a technique where a program makes a system call by going through an intermediate layer, rather than directly calling the kernel. Unlike direct syscalling, where system calls bypass standard APIs (like ntdll.dll), indirect syscalling involves using other functions or libraries that may not be hooked or modified. This technique can be useful for bypassing certain security measures, since the call doesn't directly interact with the normally monitored or hooked functions. By using indirect methods, a program can still perform operations like memory management or interacting with hardware without triggering hooks or other detection mechanisms. 3.ntdll Remapping ntdll remapping is a technique where the ntdll.dll file itself is modified or replaced with a different version to avoid detection or bypass hooks. In this approach, instead of hooking individual functions in ntdll.dll, attackers or advanced users replace or alter the ntdll.dll library that the system loads, effectively changing how system calls are handled. This can be done by mapping a custom version of ntdll.dll into memory. The modified version could have the hooks removed or altered, allowing the program to make system calls without interference. This method can be used to evade security software that relies on detecting modifications to ntdll.dll or to hide the actions of malicious programs. 4.Blocking Non-Microsoft DLLs from Loading Blocking non-Microsoft DLLs from loading in a process is a technique used to restrict which dynamic link libraries (DLLs) a program can load, specifically preventing non-Microsoft or unauthorized DLLs from being injected or loaded into a process. This is often done for security reasons, such as protecting against malware or ensuring that only trusted, signed libraries are used. When a program starts, the operating system loads necessary DLLs into memory to provide functions or services. By blocking non-Microsoft DLLs, you ensure that only known, signed libraries (usually from Microsoft or trusted sources) are allowed. This is typically done by monitoring the DLL loading process and checking the file signature, path, or origin of each DLL before it is loaded into the program’s memory space. Also here is my personal comment on each of them: Direct syscalling is kindda risky and can trigger some alerts and hence i would not recommend it , also the same applies to indirect syscalling its a little bit better than direct one but still it is risky. Ntdll remapping is also suspicious like why would a process would want to remap its ntdll? There is a way to work this way through but i will mention it on later posts. Finnaly blocking non-microsoft dlls is also kindda suspicoius.