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NTFS File Attributes

Every New Technology File System (NTFS) formatted partition contains a Master File Table (MFT) that maintains a record for every file/directory on the partition. [1] Within MFT entries are file attributes, [2] such as Extended Attributes (EA) and Data [known as Alternate Data Streams (ADSs) when more than one Data attribute is present], that can be used to store arbitrary data (and even complete files). [1] [3] [4] [5]

Adversaries may store malicious data or binaries in file attribute metadata instead of directly in files. This may be done to evade some defenses, such as static indicator scanning tools and anti-virus. [6] [4]

ID: T1096

Tactic: Defense Evasion

Platform:  Windows

Data Sources:  File monitoring, Kernel drivers, API monitoring, Process command-line parameters

Defense Bypassed:  Signature-based detection, Host forensic analysis, Anti-virus

Contributors:  Red Canary, Oddvar Moe

Version: 1.0

Examples

NameDescription
Gazer

Gazer stores configuration items in alternate data streams (ADSs) if the Registry is not accessible.[7]

PowerDuke

PowerDuke hides many of its backdoor payloads in an alternate data stream (ADS).[8]

POWERSOURCE

If the victim is using PowerShell 3.0 or later, POWERSOURCE writes its decoded payload to an alternate data stream (ADS) named kernel32.dll that is saved in %PROGRAMDATA%\Windows\.[9]

Regin

The Regin malware platform uses Extended Attributes to store encrypted executables.[10]

Zeroaccess

Some variants of the Zeroaccess Trojan have been known to store data in Extended Attributes.[11]

Mitigation

It may be difficult or inadvisable to block access to EA and ADSs. [5] [12] Efforts should be focused on preventing potentially malicious software from running. Identify and block potentially malicious software that may contain functionality to hide information in EA and ADSs by using whitelisting [13] tools like AppLocker [14] [15] or Software Restriction Policies [16] where appropriate. [17]

Consider adjusting read and write permissions for NTFS EA, though this should be tested to ensure routine OS operations are not impeded. [18]

Detection

Forensic techniques exist to identify information stored in NTFS EA. [6] Monitor calls to the ZwSetEaFile and ZwQueryEaFile Windows API functions as well as binaries used to interact with EA, [19] [20] and consider regularly scanning for the presence of modified information. [1]

There are many ways to create and interact with ADSs using Windows utilities. Monitor for operations (execution, copies, etc.) with file names that contain colons. This syntax (ex: file.ext:ads[.ext]) is commonly associated with ADSs. [5] [19] [20] For a more exhaustive list of utilities that can be used to execute and create ADSs, see https://gist.github.com/api0cradle/cdd2d0d0ec9abb686f0e89306e277b8f.

The Streams tool of Sysinternals can be used to uncover files with ADSs. The dir /r command can also be used to display ADSs. [12] Many PowerShell commands (such as Get-Item, Set-Item, Remove-Item, and Get-ChildItem) can also accept a -stream parameter to interact with ADSs. [4] [5]

References