Suspicious Access to Sensitive File Extensions — Sigma Rule

Rule metadata and linked tags

Author: Samir Bousseaden. Source status: test; severity: medium. Source dates: 2019-04-03 / 2025-10-17.

{
  "product": "windows",
  "service": "security"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: a1276123a079fe5816edfa54c7cfda5183bb9058534a5b6fb9fa1c4673ec375c

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

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

Original YAML and metadata in JSON

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

Source references

• Internal Research (source note; no public URL supplied)