Suspicious Access to Sensitive File Extensions - Zeek

Description

Detects known sensitive file extensions via Zeek

Query · sigma

selection:
  name|endswith:
  - .pst
  - .ost
  - .msg
  - .nst
  - .oab
  - .edb
  - .nsf
  - .bak
  - .dmp
  - .kirbi
  - .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 - Zeek · Sigma
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Published by SigmaHQ/sigma ↗, licensed under Detection Rule License 1.1 ↗. Reproduced here unmodified. 
title: Suspicious Access to Sensitive File Extensions - Zeek
id: 286b47ed-f6fe-40b3-b3a8-35129acd43bc
related:
    - id: 91c945bc-2ad1-4799-a591-4d00198a1215
      type: derived
status: test
description: Detects known sensitive file extensions via Zeek
references:
    - Internal Research
author: Samir Bousseaden, @neu5ron
date: 2020-04-02
modified: 2025-10-17
tags:
    - attack.collection
logsource:
    product: zeek
    service: smb_files
detection:
    selection:
        name|endswith:
            - '.pst'
            - '.ost'
            - '.msg'
            - '.nst'
            - '.oab'
            - '.edb'
            - '.nsf'
            - '.bak'
            - '.dmp'
            - '.kirbi'
            # - '\groups.xml'  # Commented out: groups.xml is accessed legitimately by Group Policy processing; high FP rate in enterprise environments
            - '.rdp'
    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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