The Rise of In-Memory PE Loaders: A New Threat to EDR Systems
A burgeoning technique enables cyber adversaries to execute malicious code directly within memory, posing formidable challenges for contemporary Endpoint Detection and Response (EDR) frameworks.
This strategy, which employs an in-memory Portable Executable (PE) loader, allows malevolent actors to run executable files inside a trusted process, effectively evading security measures that primarily scrutinize write operations to disk. Loading PE in Memory
As reported by a source known as G3tSyst3m, this tactic exposes critical vulnerabilities within various security paradigms, facilitating the covert deployment of secondary payloads subsequent to initial system infiltration.
This “fileless” attack modality is particularly insidious, operating beneath the radar. An EDR solution may initially validate a legitimate application, deeming it secure for execution.
Yet, once the trusted process is active, it can be exploited to reconfigure and execute another PE file—such as a remote access trojan or information-stealer—entirely within its own memory space.
Because the nefarious executable never interacts with the file system, conventional antivirus and EDR mechanisms, reliant on file scanning and disk-based heuristics, may remain oblivious to this threat.
The Mechanism of In-Memory PE Loaders
The attack initiates by leveraging an authentic process to retrieve a PE file from a remote avenue, such as a GitHub repository.
Utilizing standard Windows APIs like InternetOpenUrlA InternetReadFileThis code extracts the executable and stores it in a volatile memory buffer.
This primary operation often masquerades as benign network activity, allowing the payload to seamlessly infiltrate the target system without triggering alerts. Once the PE file resides in memory as a byte array, the loader systematically reconstructs it for execution. Putty downloaded using PE
This reconstruction meticulously emulates the functionalities of the Windows operating system’s loader. Principally, the loader performs several vital operations:
- Parses PE Headers: It examines the DOS and NT headers of the retrieved file to ascertain its structure, including sections and dependencies.
- Allocates Memory: It employs
VirtualAllocto reserve a segment of memory within the host process for mapping the executable image. - Maps Sections: The loader transfers the PE headers and sections (like
.textfor executable code and.datafor static variables) from the buffer into the newly allocated memory regions in accordance with their virtual addresses. - Resolves Imports: It loads necessary Dynamic-Link Libraries (DLLs) and resolves the addresses of external functions required for the PE to execute, using
LoadLibraryAandGetProcAddress. - Applies Relocations: It modifies any hardcoded addresses in the code to ensure they are correctly aligned within memory.
Upon successful mapping of the PE file and resolution of its dependencies, the concluding steps involve adjusting memory permissions and initiating execution, as explicated by G3tSyst3m.
The loader utilizes VirtualProtect to establish the appropriate permissions for each section; for example, designating the code section as executable while marking the data sector as readable and writable.
This mimics the operations of a legitimately loaded program and is critical for ensuring the code functions without disrupting the process. Once the memory is adequately configured, the loader invokes the PE file’s entry point, executing the malicious code.
This technique has demonstrated efficacy in red team engagements, successfully bypassing prominent EDR solutions such as Microsoft Defender for Endpoint (XDR) and Sophos XDR.
While not infallible—especially against advanced AI and machine learning-driven detection that can identify anomalous process behavior over time—custom-designed PE loaders remain a potent means of evading oversight.
This approach illustrates the pressing necessity for security solutions capable of conducting comprehensive memory inspections and behavioral analyses, moving beyond a mere reliance on file-based threat intelligence.
Source link: Cybersecuritynews.com.
