UserAssist

UserAssist is a feature of the Windows operating system that keeps track of the programs that are launched on a user's profile. This information is stored in the registry, a database that contains configuration settings for the operating system and other software. In this blog post, we'll explore what UserAssist is, its normal use cases, and how it can be abused by malicious actors.

Normal Use Cases

UserAssist is designed to provide a quick and convenient way for users to launch their frequently used programs. Whenever a user launches a program, Windows stores the information in the UserAssist registry key. This information is then used to generate a list of recently used programs that can be accessed through the Start menu or the Run dialog box.

The UserAssist key is a registry key within the Windows operating system that stores information about a user's activity on the system. The key is stored within the registry, which is a hierarchical database that contains configuration information for the operating system and its applications. The UserAssist key is located under the following path in the registry:

NTUSER.DAT\Software\Microsoft\Windows\CurrentVersion\Explorer\UserAssist\

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\UserAssist

This key contains several subkeys, each of which correspond to a different type of user activity, such as running applications, opening files, and using the Start menu. The information stored within the UserAssist key is encoded, but can be decoded to reveal the specific applications, files, and other items that the user has interacted with.

In this example I have used CyberChef to decode the ROT13. However there are other tools that will do this automagically for you. Two of the fan favorites would probably be:

Access Data - Registry Viewer
EricZimmerman - Registry Explorer

The UserAssist key is an important part of the Windows operating system and can be a valuable resource for digital forensics investigations, as it can provide information on a user's activity on the system, including the applications and files they have used, as well as the frequency and timing of their usage. This information can be used to help determine the user's intent, establish a timeline of events, and identify any malicious activity.

One of the primary benefits of UserAssist is that it makes it easier for users to find and launch programs that they use frequently. This can be especially useful for users who have a lot of programs installed on their computer. With UserAssist, users can launch their most frequently used programs with just a few clicks, rather than having to search through the Start menu or the list of installed programs.

Another use case for UserAssist is to keep track of programs that are launched automatically at startup. For example, if a user wants to ensure that a particular program launches every time they log in to their computer, they can add the program to the UserAssist registry key. This makes it easy for users to keep track of which programs are launching automatically and to modify the list if necessary.

Malicious Use Cases

While UserAssist can be a helpful tool for users, it can also be abused by malicious actors. One way that UserAssist can be used for malicious purposes is to track the programs that a user launches. This information can then be used to build a profile of the user's behavior and habits, which can be used for malicious purposes such as targeted advertising or identity theft.

Another way that UserAssist can be abused is through the creation of malicious registry keys. Attackers can create registry keys that are designed to launch malicious programs or to execute malicious code. These registry keys can be disguised as legitimate programs, making it difficult for users to detect the presence of malicious activity on their computer.

For example, an attacker could create a registry key that launches a malicious program whenever a user launches a commonly used program such as Microsoft Word. This would allow the attacker to execute their malicious code every time the user launches the program, potentially stealing sensitive information or causing other harm to the user's computer.

Conclusion

UserAssist is a useful feature of the Windows operating system that provides a convenient way for users to launch their frequently used programs. However, it can also be abused by malicious actors for malicious purposes. Users can protect themselves by being aware of the potential risks associated with UserAssist and by using security software to detect and prevent malicious activity.

In summary, UserAssist can be a valuable tool for users, but it's important to be mindful of the potential risks associated with its use. By understanding both the normal and malicious use cases for UserAssist, users can make informed decisions about how they use this feature and protect their computers from malicious activity.

Extra Guide:

The SANS Institute is a well-known organization that provides information security training and research. While I couldn't find a specific SANS poster on UserAssist, they do have a resource called the SANS Forensics Poster, which provides a comprehensive overview of the Windows registry and how it can be used in digital forensics investigations.

This poster provides a detailed visualization of the Windows registry, including the UserAssist key. It also provides information on how to use the registry in digital forensics investigations, including how to determine when a program was last executed and how to identify malicious activity.

https://www.sans.org/posters/windows-forensic-analysis/

Additional resources:

Microsoft Developer Network (MSDN) documentation: This official Microsoft website provides information on the UserAssist registry key, including its structure and how to use it. The page can be found at:

Microsoft Docs: UserAssist