Prefetch

Purpose and Function

Prefetching is a performance enhancement feature integrated into Windows, designed to decrease application startup times. The operating system, through the SysMain service (formerly known as Superfetch), monitors the files and data an application accesses during its initial launch phase (typically the first 10 seconds). It then records this information in a corresponding Prefetch file (.pf). On subsequent launches, Windows uses this data to proactively load necessary resources into memory, aiming for a faster and more efficient startup.

From a Digital Forensics and Incident Response (DFIR) perspective, this performance feature creates one of the most reliable and valuable artifacts for tracking program execution. The creation and modification of .pf files serve as a direct log of application launches on the system.

Location and Naming Convention

Prefetch files are stored in a dedicated system folder, which typically requires administrator privileges to access:

• Location: C:\Windows\Prefetch

Each .pf file corresponds to a specific executable run from a specific location and follows a consistent naming pattern:

EXECUTABLENAME.EXE-HASH.pf

• EXECUTABLENAME.EXE: The name of the executable file that was launched (e.g., NOTEPAD.EXE, VAPE.EXE).

• HASH: An 8-character hexadecimal hash. Crucially, this hash is calculated based on the full path from which the executable was run, not the file's content. This means that running the same executable from two different locations (e.g., C:\Users\Admin\Desktop\cheat.exe vs. C:\Users\Admin\Downloads\cheat.exe) will generate two distinct .pf files with different hashes.

Internal Structure and Stored Metadata

Each .pf file is a binary file containing a wealth of metadata that can be parsed with specialized tools. This metadata provides a detailed record of an application's execution history:

• Executable Name: The filename of the program that was launched.

• Run Count: The total number of times the application has been executed from that specific path.

• Timestamps:

  • Last Execution Time: A high-precision timestamp indicating the exact last time the application was run from that path. Forensically, the Date Modified timestamp of the .pf file itself directly mirrors this value.

  • Previous Execution Times: Up to 8 of the most recent previous execution timestamps are stored within the file, providing a short-term historical view of launches from that specific path.

• Volume Information: Details about the disk volume where the executable resided during its last run, including the volume path (e.g., \Device\HarddiskVolume1), creation date, and serial number. This is vital for tracking executions from removable media like USB drives.

• Referenced Files and Directories: A list of the specific files (including DLLs, configuration files, etc.) and directories that the application accessed during its initial startup. This is a forensically critical piece of information, as it can link a generic host process (like java.exe or rundll32.exe) to a specific malicious payload (like a .jar cheat or an injected .dll).

System Dependencies and Control

The Prefetching mechanism is not standalone; it relies on and is controlled by specific system components:

• SysMain Service: The entire Prefetching functionality is managed by the SysMain service. If this service is stopped or disabled, Windows will cease to create or update .pf files. Its status can be checked via sc query sysmain.

• Registry Control: The operational state of the Prefetcher is configured in the Windows Registry at: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters

  The EnablePrefetcher DWORD value within this key determines its behavior:

  • 0: Disabled

  • 1: Application launch prefetching enabled

  • 2: Boot prefetching enabled

  • 3: Application and Boot prefetching enabled (Default)

A non-default value, especially 0, is a strong indicator of deliberate tampering.

Forensic Value

The forensic value of Prefetch files is immense. They provide a reliable, high-precision timeline of when applications were run on a system. Because they log the full executable name (including extension), referenced files, and are tied to a specific execution path, they are a cornerstone artifact for:

• Confirming the execution of malicious software.

• Establishing a timeline of an attacker's actions.

• Identifying programs run from unusual locations or removable media.

• Discovering attempts to disguise executables by changing their file extensions.

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Reflection points (SS Contest)

For a ScreenSharer, Prefetch is a primary source of high-confidence evidence.

• High-Precision Proof: The "Last Execution Time" is precise enough to prove "in instance" execution, correlating directly with the gameplay session.

• Detecting Evasion: The file naming convention makes evasion techniques obvious. Finding a file like MyCheat.tmp-A1B2C3D4.pf is a clear indicator of a spoofed extension.

• Linking Host Processes: The "Referenced Files" list is the key to connecting the dots. It allows an SSer to definitively prove that a specific javaw.exe process loaded a cheat .jar file, or that rundll32.exe was used to load a specific cheat .dll.

• Evidence of Tampering: An empty Prefetch folder (when the service is running and the registry key is enabled) is strong evidence of clearing. A .pf file with the Read-Only attribute set is a direct attempt to "freeze" the artifact and hide recent activity. Finding the SysMain service stopped or the EnablePrefetcher registry value set to 0 is, in itself, a highly suspicious act of tampering.