macOS ESF Sensitive File Access

Status: experimental
Severity: high
Log source: product macos, service endpointsecurity
Author: Eric Brown - Nebulock, Inc.
Source: github.com/Nebulock-Inc/macos-coresigma

Detect access to sensitive system files via ESF OPEN notifications. More suspicious when non-root users access these files.

Known false positives

legitimate administrative tasks (e.g., configuration management)
root user administrative access

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	No specific technique

Rule body

title: macOS ESF Sensitive File Access
id: 3c9e1ec5-6f6c-4c9d-bb3a-1b7cf0b9a1df
status: experimental
description: Detect access to sensitive system files via ESF OPEN notifications. More suspicious when non-root users access these files.
author: Eric Brown - Nebulock, Inc.
date: 2025-10-29
logsource:
  product: macos
  service: endpointsecurity
level: high
detection:
  selection_event:
    esf.event_type: 10
    event.action: open
  selection_path:
    TargetFilename|startswith:
    - /etc/hosts
    - /etc/sudoers
    - /Library/Preferences/com.apple.TCC.plist
  selection_root:
    UserId: 0
  condition: selection_event and selection_path and not selection_root
falsepositives:
- legitimate administrative tasks (e.g., configuration management)
- root user administrative access
tags:
- attack.discovery
modified: 2025/01/15

Stages and Predicates

Stage 0: `condition`

selection_event and selection_path and not selection_root

Stage 1: `selection_event`

selection_event:
  esf.event_type: 10
  event.action: open

Stage 2: `selection_path`

selection_path:
  TargetFilename|startswith:
  - /etc/hosts
  - /etc/sudoers
  - /Library/Preferences/com.apple.TCC.plist

Stage 3: `not selection_root`

selection_root:
  UserId: 0

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`UserId`	eq	`0`	`excludes:UserId` `field:"UserId" value:"0"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`TargetFilename`	starts_with	`/Library/Preferences/com.apple.TCC.plist` `/etc/hosts` `/etc/sudoers`	`field:"TargetFilename" kind:starts_with`
`esf.event_type`	eq	`10`	`field:"esf.event_type" kind:eq value:"10"`
`event.action`	eq	`open`	`field:"EventType" kind:eq value:"open"`