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|Data Sources||Process: OS API Execution|
|Asset||Control Server, Data Historian, Field Controller/RTU/PLC/IED, Human-Machine Interface, Input/Output Server, Safety Instrumented System/Protection Relay|
Adversaries may directly interact with the native OS application programming interface (API) to access system functions. Native APIs provide a controlled means of calling low-level OS services within the kernel, such as those involving hardware/devices, memory, and processes.1 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.
Functionality provided by native APIs are often also exposed to user-mode applications via interfaces and libraries. For example, functions such as memcpy and direct operations on memory registers can be used to modify user and system memory space.
- PLC-Blaster uses the system function blocks TCON and TDISCON to initiate and destroy TCP connections to arbitrary systems. Buffers may be sent and received on these connections with TRCV und TSEND system function blocks.2
- Stuxnet calls system function blocks which are part of the operating system running on the PLC. They’re used to execute system tasks, such as reading the system clock (SFC1) and generating data blocks on the fly.3
- Triton's imain.bin payload takes commands from the TsHi.ExplReadRam(Ex), TsHi.ExplWriteRam(Ex) and TsHi.ExplExec functions to perform operations on controller memory and registers using syscalls written in PowerPC shellcode.4
- Execution Prevention - Minimize the exposure of API calls that allow the execution of code.