In digital forensics and incident response (DFIR), the ability to analyze artifacts efficiently is critical to uncovering malicious activity. One such powerful tool is PECmd, developed by renowned forensic expert Eric Zimmerman. PE (Prefetch) files can provide valuable insights into program execution history on a Windows system, making PECmd an essential tool for forensic investigations.
What is Prefetch Analysis?
Prefetch analysis is the forensic process of examining Windows Prefetch files (.pf) to reconstruct the execution history of programs on a system. These files contain metadata such as:
- Last execution timestamp – When the program was last run.
- Run count – The number of times the program has been executed.
- File paths – The location of the executable and associated files.
- Referenced DLLs – Libraries loaded by the program.
Since Windows Prefetching is designed to optimize system performance by caching frequently used applications, forensic analysts can use Prefetch files to track user activity, detect malicious executions, and analyze malware behavior.
What is PECmd?
PECmd is a forensic command-line tool that parses Windows Prefetch files. Prefetch is a performance optimization feature in Windows, which stores metadata about recently executed programs, including timestamps, file paths, and execution count. This information is invaluable for identifying executed malware, unauthorized programs, and suspicious user activity.
Why is Prefetch Analysis Important for DFIR?
Prefetch files can be a goldmine for incident responders and forensic analysts, providing evidence of program execution even after the binary has been deleted. Prefetch analysis is particularly useful in the following scenarios:
- Incident Response: Quickly identify malware execution and persistence.
- Insider Threat Investigations: Detect unauthorized software or suspicious script executions.
- Timeline Reconstruction: Correlate program execution with other forensic artifacts like event logs and registry changes.
- Anti-Forensics Detection: If Prefetch files are missing, it could indicate deliberate tampering or an attempt to cover tracks.
Key Features of PECmd
- Fast and Efficient Parsing: PEcmd processes large volumes of Prefetch files quickly.
- Detailed Report Generation: It extracts execution timestamps, file paths, and process metadata.
- SQLite and CSV Output: Exports results in various formats for deeper analysis.
- Batch Processing: Analyzes multiple Prefetch files at once.
- Works with Deleted Prefetch Files: Can recover artifacts even from unallocated disk space.
How to Use PEcmd for Forensic Analysis
Installation
PECmd is part of Eric Zimmerman’s suite of forensic tools. You can download it from Eric Zimmerman’s GitHub repository.
Running PEcmd
After downloading, extract the files and navigate to the directory in the command prompt.
Basic Command
PECmd.exe -d C:\Windows\PrefetchThis command will process all Prefetch files in the specified directory.
Exporting to CSV
PECmd.exe -d C:\Windows\Prefetch -csv output.csvThis exports the parsed Prefetch data into a CSV file for further analysis.
Parsing a Single Prefetch File
PECmd.exe -f C:\Windows\Prefetch\notepad.exe-3AE4F9.pfAnalyzes a specific Prefetch file and extracts metadata.
Practical Use Cases in Incident Response
- Malware Execution Tracking:
- Identify whether malicious binaries (e.g., ransomware, droppers) were executed.
- Determine the exact execution time and frequency.
- User Activity Monitoring:
- Track which programs users ran before or during an incident.
- Find evidence of unauthorized tool usage (e.g., hacking tools, PowerShell scripts).
- System Compromise Investigation:
- Detect anomalies in execution patterns.
- Link Prefetch artifacts to other forensic artifacts like event logs and registry entries.
- Identify fileless malware or obfuscated attack techniques that bypass traditional detection.