Adversaries may inject malicious code into suspended and hollowed processes in order to evade process-based defenses. Process hollowing is a method of executing arbitrary code in the address space of a separate live process.
Process hollowing is commonly performed by creating a process in a suspended state then unmapping/hollowing its memory, which can then be replaced with malicious code. A victim process can be created with native Windows API calls such as
CreateProcess, which includes a flag to suspend the processes primary thread. At this point the process can be unmapped using APIs calls such as
NtUnmapViewOfSection before being written to, realigned to the injected code, and resumed via
This is very similar to Thread Local Storage but creates a new process rather than targeting an existing process. This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process hollowing may also evade detection from security products since the execution is masked under a legitimate process.
|M1040||Behavior Prevention on Endpoint||
Some endpoint security solutions can be configured to block some types of process injection based on common sequences of behavior that occur during the injection process.
|ID||Data Source||Data Component|
|DS0009||Process||OS API Execution|
Monitoring Windows API calls indicative of the various types of code injection may generate a significant amount of data and may not be directly useful for defense unless collected under specific circumstances for known bad sequences of calls, since benign use of API functions may be common and difficult to distinguish from malicious behavior. Windows API calls such as
ResumeThread, and those that can be used to modify memory within another process, such as
WriteProcessMemory, may be used for this technique.
Analyze process behavior to determine if a process is performing actions it usually does not, such as opening network connections, reading files, or other suspicious actions that could relate to post-compromise behavior.