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T1564.005 Hidden File System

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.1

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.12 Another implementation could be for an adversary to drop their own portable partition image as a file on top of the standard file system.3 Adversaries may also fragment files across the existing file system structure in non-standard ways.4

Item Value
ID T1564.005
Sub-techniques T1564.001, T1564.002, T1564.003, T1564.004, T1564.005, T1564.006, T1564.007, T1564.008, T1564.009, T1564.010
Tactics TA0005
Platforms Linux, Windows, macOS
Permissions required Administrator, User
Version 1.0
Created 28 June 2020
Last Modified 29 June 2020

Procedure Examples

ID Name Description
S0114 BOOTRASH BOOTRASH has used unallocated disk space between partitions for a hidden file system that stores components of the Nemesis bootkit.2
S0126 ComRAT ComRAT has used a portable FAT16 partition image placed in %TEMP% as a hidden file system.3
G0020 Equation Equation has used an encrypted virtual file system stored in the Windows Registry.4
S0019 Regin Regin has used a hidden file system to store some of its components.5
G0041 Strider Strider has used a hidden file system that is stored as a file on disk.6

Detection

ID Data Source Data Component
DS0022 File File Modification
DS0001 Firmware Firmware Modification
DS0024 Windows Registry Windows Registry Key Modification

References

  1. Hutchins, M. (2014, November 28). Virtual File Systems for Beginners. Retrieved June 22, 2020. ↩↩

  2. Andonov, D., et al. (2015, December 7). Thriving Beyond The Operating System: Financial Threat Group Targets Volume Boot Record. Retrieved May 13, 2016. ↩↩

  3. Faou, M. (2020, May). From Agent.btz to ComRAT v4: A ten-year journey. Retrieved June 15, 2020. ↩↩

  4. Kaspersky Lab’s Global Research and Analysis Team. (2015, February). Equation Group: Questions and Answers. Retrieved December 21, 2015. ↩↩

  5. Kaspersky Lab’s Global Research and Analysis Team. (2014, November 24). THE REGIN PLATFORM NATION-STATE OWNAGE OF GSM NETWORKS. Retrieved December 1, 2014. ↩

  6. Kaspersky Lab’s Global Research & Analysis Team. (2016, August 9). The ProjectSauron APT. Retrieved August 17, 2016. ↩