Zone.Identifer

The Zone.Identifier alternate data stream (ADS) is an integral part of Windows' security framework, tagging files downloaded from the Internet with metadata that includes the file's origin. This functionality, starting from Windows XP SP2, extends through all subsequent Windows versions, applying to files saved on NTFS volumes. It serves as a mechanism for Office applications and other software to prompt users to "Trust" a downloaded file before editing, reflecting its broader implications for both security and forensic analysis.

Key Insights:

• Core Functionality: The Zone.Identifier ADS is added to files downloaded from the Internet, marking them with the MotW. This tagging is performed via the Windows API function IAttachmentExecute, which is utilized by various Internet-facing applications to safely download files.

• ZoneID Values:

  • NoZone = -1

  • MyComputer = 0

  • Intranet = 1

  • Trusted = 2

  • Internet = 3

  • Untrusted = 4 (used when Microsoft SmartScreen flags a file as suspicious)

• Application and Exceptions: While most modern browsers and Internet applications tag downloaded files with this ADS, certain command-line tools like PowerShell and ftp.exe may not. Internet Explorer, for example, has been noted to only tag certain file types.

Deeper Dive

Analytical Value of Zone.Identifier

• The Zone.Identifier ADS provides valuable insights for forensic analysts, offering a method to quickly identify downloaded files and potentially trace their origin. This includes the ZoneID, which categorizes the file's source by trust level, and may also include ReferrerURL or HostURL information, offering clues about the file's initial location on the web.

• Notably, files flagged by Microsoft SmartScreen as suspicious are marked with Untrusted=4, highlighting potential security risks.

Analyzing The Artifact

• To analyze files tagged with the Zone.Identifier ADS, forensic investigators can use tools like FTK Imager to view the ADS contents, revealing the ZoneID and any associated URLs. Tools such as Eric Zimmerman’s mftecmd.exe and The Sleuth Kit’s fls tool can identify alternate data streams within a file system, aiding in the discovery of downloaded files in unexpected locations, like C:\Windows\System32.

• Using istat and icat from The Sleuth Kit, analysts can further inspect the presence of additional data streams for a specific file and extract them for detailed examination.

Tools for Analysis

• FTK Imager: For viewing Zone.Identifier ADS and its contents.

• Eric Zimmerman's mftecmd.exe: Identifies files with ADS in a file system.

• The Sleuth Kit (TSK): fls for listing files with ADS, istat for showing ADS details, and icat for extracting ADS contents.

• Windows Sysinternals: Tools like Streams can also be used to view and manage ADS on Windows files.

The Zone.Identifier ADS is a pivotal element in the forensic analysis of downloaded files, providing essential data for tracing file origins and assessing potential security risks. Its analysis is fundamental in investigations involving downloaded content, offering insights into user behavior, file provenance, and potential malware or untrusted file interactions.