Startup

The Start Menu's Startup folders in Windows play a crucial role in the operating system's functionality by allowing programs to launch automatically upon a user's login. This feature is designed to enhance productivity by initiating essential applications without manual intervention. However, it can also be exploited by threat actors to establish persistence and execute malicious payloads stealthily upon every system start or user login.

Overview

Locations

• For All Users: C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup

• For Current User: C:\Users\[Username]\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup

These directories can contain shortcuts, scripts, or executable files that Windows will automatically execute at user login.

Malicious Use

Malware authors commonly place malicious executables or scripts in these folders to ensure their payload runs each time the user logs in. This technique provides an easy and effective method for achieving persistence, making it a popular choice among various types of malware, including spyware, ransomware, and backdoors.

Identifying Malicious Entries

1. Unusual or Unknown Applications: Any unfamiliar application or script within these folders should be investigated. Malicious entries often have non-descriptive names or mimic legitimate software names to avoid detection.

2. Verification of Digital Signatures: Check if the executable or script is digitally signed by a reputable publisher. Unsigned or poorly signed applications in the Startup folder may indicate malicious intent.

3. Location and Properties Analysis: Analyzing the file path and properties of the startup items can provide clues. Malicious files may reside in unusual directories or have suspicious attributes, such as hidden or read-only flags.

4. System Performance and Behavior: An unexpected decline in system performance or unusual network activity at startup can be indicative of malicious processes executing from the Startup folders.

Finding Additions in Logs or System Files

1. Windows Event Logs: Use Event Viewer to check for events related to software installation or errors reported by applications at startup. While direct creation of startup items might not be logged, related events can provide context or indicate unauthorized changes.

2. Prefetch Files: Windows creates prefetch files (*.pf) in C:\Windows\Prefetch to speed up the loading of applications. These files can be analyzed to determine recently added applications that are executed at startup.

3. Scheduled Tasks: Check the Task Scheduler for tasks configured to run at user logon. Malicious actors might use scheduled tasks in conjunction with or instead of Startup folder items for persistence.

4. Registry: The Registry also manages autostart locations, including but not limited to:

   • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

   • HKCU\Software\Microsoft\Windows\CurrentVersion\Run

   Monitoring these keys for new or modified entries can help identify unauthorized autostart applications.

Tools and Techniques for Analysis

• Sysinternals Autoruns: This tool provides the most comprehensive analysis of autostart locations, including Startup folders. It can identify and help disable suspicious or unnecessary autostart entries.

• Antivirus and Antimalware Scanners: Regular scans with updated security software can detect and remove malicious files from Startup folders.

• File Integrity Monitoring: Implementing file integrity monitoring on the Startup folders can alert administrators to unauthorized changes.

• Security Information and Event Management (SIEM): A SIEM system can aggregate logs from various sources, including Event Viewer, to help identify patterns indicative of malicious activity, such as the repeated failure of a startup item pointing to a malware infection.

Best Practices for Security

• Regularly audit the contents of the Startup folders for all users.

• Maintain up-to-date antivirus software to detect and remove malicious entries.

• Employ least privilege principles, restricting write access to these folders for standard users.

• Educate users on the risks of downloading and running unknown applications.