Adversaries may interact with the native OS application programming interface (API) to execute behaviors. Native APIs provide a controlled means of calling low-level OS services within the kernel, such as those involving hardware/devices, memory, and processes.(Citation: NT API Windows)(Citation: Linux Kernel API) These native APIs are leveraged by the OS during system boot (when other system components are not yet initialized) as well as carrying out tasks and requests during routine operations.

Adversaries may abuse these OS API functions as a means of executing behaviors. Similar to [Command and Scripting Interpreter](https://attack.mitre.org/techniques/T1059), the native API and its hierarchy of interfaces provide mechanisms to interact with and utilize various components of a victimized system.

Native API functions (such as <code>NtCreateProcess</code>) may be directed invoked via system calls / syscalls, but these features are also often exposed to user-mode applications via interfaces and libraries.(Citation: OutFlank System Calls)(Citation: CyberBit System Calls)(Citation: MDSec System Calls) For example, functions such as the Windows API <code>CreateProcess()</code> or GNU <code>fork()</code> will allow programs and scripts to start other processes.(Citation: Microsoft CreateProcess)(Citation: GNU Fork) This may allow API callers to execute a binary, run a CLI command, load modules, etc. as thousands of similar API functions exist for various system operations.(Citation: Microsoft Win32)(Citation: LIBC)(Citation: GLIBC)

Higher level software frameworks, such as Microsoft .NET and macOS Cocoa, are also available to interact with native APIs. These frameworks typically provide language wrappers/abstractions to API functionalities and are designed for ease-of-use/portability of code.(Citation: Microsoft NET)(Citation: Apple Core Services)(Citation: MACOS Cocoa)(Citation: macOS Foundation)

Adversaries may use assembly to directly or in-directly invoke syscalls in an attempt to subvert defensive sensors and detection signatures such as user mode API-hooks.(Citation: Redops Syscalls) Adversaries may also attempt to tamper with sensors and defensive tools associated with API monitoring, such as unhooking monitored functions via [Disable or Modify Tools](https://attack.mitre.org/techniques/T1562/001).
Native API
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1106  external_id: T1106     source_name: MACOS Cocoa  description: Apple. (2015, September 16). Cocoa Application Layer. Retrieved June 25, 2020.  url: https://developer.apple.com/library/archive/documentation/MacOSX/Conceptual/OSX_Technology_Overview/CocoaApplicationLayer/CocoaApplicationLayer.html#//apple_ref/doc/uid/TP40001067-CH274-SW1     source_name: Apple Core Services  description: Apple. (n.d.). Core Services. Retrieved June 25, 2020.  url: https://developer.apple.com/documentation/coreservices     source_name: macOS Foundation  description: Apple. (n.d.). Foundation. Retrieved July 1, 2020.  url: https://developer.apple.com/documentation/foundation     source_name: OutFlank System Calls  description: de Plaa, C. (2019, June 19). Red Team Tactics: Combining Direct System Calls and sRDI to bypass AV/EDR. Retrieved September 29, 2021.  url: https://outflank.nl/blog/2019/06/19/red-team-tactics-combining-direct-system-calls-and-srdi-to-bypass-av-edr/     source_name: Redops Syscalls  description: Feichter, D. (2023, June 30). Direct Syscalls vs Indirect Syscalls. Retrieved September 27, 2023.  url: https://redops.at/en/blog/direct-syscalls-vs-indirect-syscalls     source_name: GNU Fork  description: Free Software Foundation, Inc.. (2020, June 18). Creating a Process. Retrieved June 25, 2020.  url: https://www.gnu.org/software/libc/manual/html_node/Creating-a-Process.html     source_name: CyberBit System Calls  description: Gavriel, H. (2018, November 27). Malware Mitigation when Direct System Calls are Used. Retrieved September 29, 2021.  url: https://www.cyberbit.com/blog/endpoint-security/malware-mitigation-when-direct-system-calls-are-used/     source_name: GLIBC  description: glibc developer community. (2020, February 1). The GNU C Library (glibc). Retrieved June 25, 2020.  url: https://www.gnu.org/software/libc/     source_name: LIBC  description: Kerrisk, M. (2016, December 12). libc(7) — Linux manual page. Retrieved June 25, 2020.  url: https://man7.org/linux/man-pages//man7/libc.7.html     source_name: Linux Kernel API  description: Linux Kernel Organization, Inc. (n.d.). The Linux Kernel API. Retrieved June 25, 2020.  url: https://www.kernel.org/doc/html/v4.12/core-api/kernel-api.html     source_name: MDSec System Calls  description: MDSec Research. (2020, December). Bypassing User-Mode Hooks and Direct Invocation of System Calls for Red Teams. Retrieved September 29, 2021.  url: https://www.mdsec.co.uk/2020/12/bypassing-user-mode-hooks-and-direct-invocation-of-system-calls-for-red-teams/     source_name: Microsoft CreateProcess  description: Microsoft. (n.d.). CreateProcess function. Retrieved December 5, 2014.  url: http://msdn.microsoft.com/en-us/library/ms682425     source_name: Microsoft Win32  description: Microsoft. (n.d.). Programming reference for the Win32 API. Retrieved March 15, 2020.  url: https://docs.microsoft.com/en-us/windows/win32/api/     source_name: Microsoft NET  description: Microsoft. (n.d.). What is .NET Framework?. Retrieved March 15, 2020.  url: https://dotnet.microsoft.com/learn/dotnet/what-is-dotnet-framework     source_name: NT API Windows  description: The NTinterlnals.net team. (n.d.). Nowak, T. Retrieved June 25, 2020.  url: https://undocumented.ntinternals.net/     