Suspicious Access to Sensitive File Extensions

Description

Detects known sensitive file extensions accessed on a network share

Query · sigma

selection:
  EventID: 5145
  RelativeTargetName|endswith:
  - .bak
  - .dmp
  - .edb
  - .kirbi
  - .msg
  - .nsf
  - .nst
  - .oab
  - .ost
  - .pst
  - .rdp
condition: selection

Known false positives

  • Help Desk operator doing backup or re-imaging end user machine or backup software
  • Users working with these data types or exchanging message files
Raw source Suspicious Access to Sensitive File Extensions · Sigma
Esc
Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: Suspicious Access to Sensitive File Extensions
id: 91c945bc-2ad1-4799-a591-4d00198a1215
related:
    - id: 286b47ed-f6fe-40b3-b3a8-35129acd43bc
      type: similar
status: test
description: Detects known sensitive file extensions accessed on a network share
references:
    - Internal Research
author: Samir Bousseaden
date: 2019-04-03
modified: 2025-10-17
tags:
    - attack.collection
    - attack.t1039
logsource:
    product: windows
    service: security
detection:
    selection:
        EventID: 5145
        RelativeTargetName|endswith:
            - '.bak'
            - '.dmp'
            - '.edb'
            - '.kirbi'
            - '.msg'
            - '.nsf'
            - '.nst'
            - '.oab'
            - '.ost'
            - '.pst'
            - '.rdp'
            # - '\groups.xml'  # Commented out: groups.xml is accessed legitimately by Group Policy processing; high FP rate in enterprise environments
    condition: selection
falsepositives:
    - Help Desk operator doing backup or re-imaging end user machine or backup software
    - Users working with these data types or exchanging message files
level: medium

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