Potentially Suspicious NTFS Symlink Behavior Modification

testmedium

log source: windows · process_creationauthor frack113, The DFIR Reportdate 2022-03-02

description

What this is, in brief.

Detects the modification of NTFS symbolic link behavior using fsutil, which could be used to enable remote to local or remote to remote symlinks for potential attacks.

rule source (YAML)

title: Potentially Suspicious NTFS Symlink Behavior Modification
id: c0b2768a-dd06-4671-8339-b16ca8d1f27f
status: test
description: |
    Detects the modification of NTFS symbolic link behavior using fsutil, which could be used to enable remote to local or remote to remote symlinks for potential attacks.
references:
    - https://www.cybereason.com/blog/cybereason-vs.-blackcat-ransomware
    - https://learn.microsoft.com/fr-fr/windows-server/administration/windows-commands/fsutil-behavior
    - https://thedfirreport.com/2025/06/30/hide-your-rdp-password-spray-leads-to-ransomhub-deployment/
author: frack113, The DFIR Report
date: 2022-03-02
modified: 2025-11-13
tags:
    - attack.execution
    - attack.defense-impairment
    - attack.t1059
    - attack.t1222.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img_proxy:
        # Note: Example command observed:  cmd.exe /c "fsutil behaviour set SymlinkEvaluation"
        - Image|endswith:
              - '\cmd.exe'
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'Cmd.Exe'
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_fsutil_cli:
        CommandLine|contains|all:
            - 'fsutil'
            - 'behavior'
            - 'set'
            - 'SymlinkEvaluation'
    selection_symlink_params:
        CommandLine|contains:
            - 'R2L:1' # Remote to Local
            - 'R2R:1' # Remote to Remote
            - 'L2L:1' # Local to Local
    condition: all of selection_*
falsepositives:
    - Legitimate usage, investigate the parent process and context to determine if benign.
level: medium
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_fsutil_symlinkevaluation/info.yml

detects techniques (2)

ATT&CK techniques this enables or maps to.

references

External citations — patches, advisories, analysis.