Access To Windows DPAPI Master Keys By Uncommon Applications

Status: test
Severity: medium
Log source: category file_access, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects file access requests to the the Windows Data Protection API Master keys by an uncommon application. This can be a sign of credential stealing. Example case would be usage of mimikatz "dpapi::masterkey" function

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1555.004` Credentials from Password Stores: Windows Credential Manager

Rule body

title: Access To Windows DPAPI Master Keys By Uncommon Applications
id: 46612ae6-86be-4802-bc07-39b59feb1309
status: test
description: |
    Detects file access requests to the the Windows Data Protection API Master keys by an uncommon application.
    This can be a sign of credential stealing. Example case would be usage of mimikatz "dpapi::masterkey" function
references:
    - http://blog.harmj0y.net/redteaming/operational-guidance-for-offensive-user-dpapi-abuse/
    - https://book.hacktricks.xyz/windows-hardening/windows-local-privilege-escalation/dpapi-extracting-passwords
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-10-17
modified: 2026-07-28
tags:
    - attack.credential-access
    - attack.t1555.004
logsource:
    category: file_access
    product: windows
    definition: 'Requirements: Microsoft-Windows-Kernel-File ETW provider'
detection:
    selection:
        FileName|contains:
            - '\Microsoft\Protect\S-1-5-18\' # For System32
            - '\Microsoft\Protect\S-1-5-21-' # For Users
    filter_main_system_folders:
        Image|startswith:
            - 'C:\Program Files\'
            - 'C:\Program Files (x86)\'
            - 'C:\Windows\system32\'
            - 'C:\Windows\SysWOW64\'
    filter_main_explorer:
        Image: 'C:\Windows\explorer.exe'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
# Increase level after false positives filters are good enough
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_*

Stage 1: `selection`

selection:
    FileName|contains:
        - '\Microsoft\Protect\S-1-5-18\'
        - '\Microsoft\Protect\S-1-5-21-'

Stage 2: `not filter_main_*`

filter_main_system_folders:
    Image|startswith:
        - 'C:\Program Files\'
        - 'C:\Program Files (x86)\'
        - 'C:\Windows\system32\'
        - 'C:\Windows\SysWOW64\'
filter_main_explorer:
    Image: 'C:\Windows\explorer.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	eq	`C:\Windows\explorer.exe`	`excludes:Image` `field:"Image" value:"C:\Windows\explorer.exe"`
`Image`	starts_with	`C:\Program Files (x86)\`	`excludes:Image` `field:"Image" value:"C:\Program Files (x86)\"`
`Image`	starts_with	`C:\Program Files\`	`excludes:Image` `field:"Image" value:"C:\Program Files\"`
`Image`	starts_with	`C:\Windows\SysWOW64\`	`excludes:Image` `field:"Image" value:"C:\Windows\SysWOW64\"`
`Image`	starts_with	`C:\Windows\system32\`	`excludes:Image` `field:"Image" value:"C:\Windows\system32\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`FileName`	match	`\Microsoft\Protect\S-1-5-18\` `\Microsoft\Protect\S-1-5-21-`	`field:"file_name" kind:match`