Open/Save Most Recently Used (MRU)

The Open/Save Most Recently Used (MRU) feature is a key component of the Windows operating system that memorizes the files and directories a user has recently accessed. This mechanism, integrated into the Windows user interface, simplifies file retrieval and enhances user efficiency by reducing the need for extensive navigation through file systems. The MRU system supports a wide range of applications, making it a ubiquitous element of the Windows user experience.

Key Insights:

• Registry Storage:

  • General Path: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\ComDlg32\OpenSavePIDlMRU

  • Windows XP Path: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\ComDlg32\OpenSaveMRU

• Format and Content: The registry contains values named after file extensions or identifiers (like * for all files), with paths stored in binary or string formats. Additionally, individual applications may maintain their own MRU lists in specific registry paths or configuration files.

Deeper Dive

Forensic Importance in Incident Response

• Timeline Analysis: The timestamps associated with MRU entries can be instrumental in constructing a timeline of events, helping to pinpoint when specific files were accessed.

• User Behavior Insight: Analyzing the contents of MRU lists can provide a glimpse into user behavior, including file interactions that might indicate unauthorized access or interest in sensitive information.

• Malware Indicators: MRU paths leading to executable files or documents that are known vectors for malware can serve as indicators of a security breach.

• Evidence Corroboration: Data from MRU entries can corroborate findings from other digital artifacts, providing a more comprehensive understanding of an incident.

User Interface Reflection

• The Open and Save dialog boxes in Windows applications utilize MRU data to display a list of recent documents, streamlining the file access process. Similarly, the Quick Access or Recent Documents sections in File Explorer aggregate MRU data to highlight frequently used files and folders.

• Jump Lists, accessible by right-clicking an application on the taskbar, also draw from MRU entries to present a list of recently opened files associated with that application.

Forensic Relevance

• The convenience features provided by the MRU system, while primarily designed to enhance user efficiency, can also be leveraged in forensic investigations. The data captured by Open/Save MRU entries offers a window into user behavior, revealing patterns that might otherwise remain hidden. This information can be especially valuable in cases involving data breaches, unauthorized file access, or the introduction of malware into a system.

Practical Example

• In investigating a data breach, an analyst might discover MRU entries pointing to unusual file types or locations, such as external drives or network paths not typically accessed by the user. These entries, when analyzed alongside other digital evidence like access logs, can offer vital clues to the methods and pathways utilized in the breach, aiding in the reconstruction of the incident and the identification of potential security lapses.

The Open/Save MRU feature, by keeping a record of recently accessed files and directories, not only simplifies file operations for users but also serves as a significant artifact in digital forensics. Its analysis can reveal a wealth of information about user activities, offering insights that are critical in the context of incident response and investigation.