As a red team member, having various tools and techniques is essential for achieving your objectives. One technique that can be extremely useful for red teams is the ability to hide data on a Windows NTFS file system using alternate data streams. This technique can conceal sensitive information from network defenders and blue teams. In this article, we will explore alternate data streams, how they can be used to hide data, some examples of their use, and how to detect them.

What are Alternate Data Streams?

Alternate data streams (ADS) are a feature of the Windows NTFS file system that allows additional data to be attached to a file without changing the file’s primary data stream. This feature was initially intended to support compatibility with the Macintosh Hierarchical File System (HFS), which also allowed for alternate data streams. However, this feature has since been used for other purposes, including hiding data from prying eyes.

How to Hide Data Using Alternate Data Streams

Hiding data using alternate data streams can be accomplished using built-in Windows tools or third-party software. The simplest way to create an alternate data stream is to use the command-line utility type. To do this, the user can use the type command to redirect content into an alternate stream of an existing file using the : delimiter syntax.

For example, to hide a password in a file called “example.txt”, the user could use the following command:

type password.txt >> example.txt:hidden.txt

This writes the contents of “password.txt” into the alternate data stream named “hidden.txt” attached to “example.txt”, without modifying the visible content of “example.txt”.

Alternate data streams can also be used to hide data in non-text files, such as images or executables. However, the technique is limited to NTFS volumes and is not supported on FAT32 or exFAT file systems.

Detecting Alternate Data Streams

Detecting alternate data streams can be challenging, as they are not visible in Windows Explorer or other file managers. However, several tools and techniques can be used to detect them.

One way to detect alternate data streams is to use the command line utility, dir, with the /r flag. This will display any alternate data streams that are associated with a file. For example, to display the alternate data streams related to a file called “example.txt”, the user could use the following command:

dir /r example.txt

Another tool for detecting alternate data streams is streams.exe. This is a command-line utility from Microsoft’s Sysinternals suite that can help identify and remove alternate data streams. The user can use the streams.exe command to display the alternate data streams associated with a file and then use other tools to extract or analyze the data.

Implications of Using Alternate Data Streams to Hide Data

While using alternate data streams to hide data can be an effective way to keep sensitive information hidden from prying eyes, several implications should be considered before using this technique. One of the main implications is that this technique may be illegal in some jurisdictions, as it can be used to hide unlawful content, such as child pornography or stolen intellectual property. Additionally, using alternate data streams to hide data can violate user trust and may be a breach of ethical standards.

Another implication of using alternate data streams to hide data is that it may not be as secure as it seems. While alternate data streams can effectively hide data from casual users, they may not withstand a determined attacker. A knowledgeable attacker may be able to detect the presence of an alternate data stream on a file and extract the hidden data. Additionally, using alternate data streams to hide data may be detected by anti-virus software, which can lead to false positives and may alert network defenders to suspicious activity.

Conclusion

The ability to hide data on a Windows NTFS file system using alternate data streams is a valuable technique that red teams can use to conceal sensitive information from prying eyes. While this technique can be useful in certain red team scenarios, it may be illegal or unethical depending on the context and jurisdiction. Additionally, using alternate data streams to hide data may not be as secure as it seems and may be detected by anti-virus software or a determined attacker. As with any technique, weighing its risks and benefits is essential.