Query: Suspicious Hidden File System execution detected on endpoint
Matching passage: T1564.005 Hidden File System. Tactics: stealth. Description: Adversaries may use a hidden file system to conceal malicious activity from users and security tools. File systems provide a structure to store and access data from physical storage. Typically, a user engages with a file system through applications that allow them to access files and directories, which are an abstraction from their physical location (ex: disk sector). Standard file systems include FAT, NTFS, ext4, and APFS. File systems can also contain other structures, such as the Volume Boot Record (VBR) and Master File Table (MFT) in NTFS.(Citation: MalwareTech VFS Nov 2014) Adversaries may use their own abstracted file system, separate from the standard file system present on the infected system. In doing so, adversaries can hide the presence of malicious components and file input/output from security tools. Hidden file systems, sometimes referred to as virtual file systems, can be implemented in numerous ways. One implementation would be to store a file system in reserved disk space unused by disk structures or standard file system partitions.(Citation: MalwareTech VFS Nov 2014)(Citation: FireEye Bootkits) Another implementation could be for an adversary to drop their own portable partition image as a file on top of the standard file system.(Citation: ESET ComRAT May 2020) Adversaries may also fragment files across the existing file system structure in non-standard ways.(Citation: Kaspersky Equation QA)
Near-miss passage: T1564.010 Process Argument Spoofing. Tactics: stealth. Description: Adversaries may attempt to hide process command-line arguments by overwriting process memory. Process command-line arguments are stored in the process environment block (PEB), a data structure used by Windows to store various information about/used by a process. The PEB includes the process command-line arguments that are referenced when executing the process. When a process is created, defensive tools/sensors that monitor process creations may retrieve the process arguments from the PEB.(Citation: Microsoft PEB 2021)(Citation: Xpn Argue Like Cobalt 2019) Adversaries may manipulate a process PEB to evade defenses. For example, [Process Hollowing](https://attack.mitre.org/techniques/T1055/012) can be abused to spawn a process in a suspended state with benign arguments. After the process is spawned and the PEB is initialized (and process information is potentially logged by tools/sensors), adversaries may override the PEB to modify the command-line arguments (ex: using the [Native API](https://attack.mitre.org/techniques/T1106) <code>WriteProcessMemory()</code> function) then resume process execution with malicious arguments.(Citation: Cobalt Strike Arguments 2019)(Citation: Xpn Argue Like Cobalt 2019)(Citation: Nviso Spoof Command Line 2020) Adversaries may also execute a process with malicious command-line arguments then patch the memory with benign arguments that may bypass subsequent process memory analysis.(Citation: FireEye FiveHands April 2021) This behavior may also be combined with other tricks (such as [Parent PID Spoofing](https://attack.mitre.org/techniques/T1134/004)) to manipulate or further evade process-based detections.