Abuse of NTFS INDEX_ALLOCATION Stream for Directory Obfuscation

This technique involves the abuse of the NTFS filesystem structure, specifically the $INDEX_ALLOCATION attribute. By appending the string "::$INDEX_ALLOCATION" to a directory name during creation, an attacker can create a folder structure that standard Windows APIs and common management tools (such as Windows Explorer or PowerShell) struggle to traverse or list. This effectively hides the directory and its contents from the average user and administrative tools, providing a method for stealthy persistence or data staging. While the data remains accessible via low-level file system calls or specific command-line utilities, this technique is frequently leveraged to bypass automated monitoring and user discovery during the post-exploitation phase. Defenders should be aware that standard EDR process-creation logs may not always capture the full command-line arguments involving alternate data streams, depending on the specific sensor implementation and visibility.

Impact

Successful implementation of this technique results in the creation of hidden directories that effectively bypass traditional file discovery methods. This allows an attacker to conceal malware payloads, exfiltrated data, or persistence mechanisms on an endpoint, reducing the likelihood of detection by security personnel and automated administrative cleanup tasks.

Recommendation

• Deploy the provided Sigma rule to detect the use of "::$index_allocation" in command-line arguments.
• Verify your EDR/telemetry coverage, as many standard Sysmon configurations do not log alternate data stream path components in process-creation events.
• Prioritize auditing file system modifications for directories containing "::$index_allocation" strings.