New File Exclusion Added To Time Machine Via Tmutil - MacOS

Status: test
Severity: medium
Log source: category process_creation, product macos
Author: Pratinav Chandra
Source: github.com/SigmaHQ/sigma

Detects the addition of a new file or path exclusion to MacOS Time Machine via the "tmutil" utility. An adversary could exclude a path from Time Machine backups to prevent certain files from being backed up.

Known false positives

Legitimate administrator activity

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1490` Inhibit System Recovery

Telemetry coverage

Platform	Record / event type
macOS	ESF event `exec` (NOTIFY): Fires after execve(2) or posix_spawn(2) succeeds, delivering a post-fact record of the new process.

Rule body

title: New File Exclusion Added To Time Machine Via Tmutil - MacOS
id: 9acf45ed-3a26-4062-bf08-56857613eb52
status: test
description: |
    Detects the addition of a new file or path exclusion to MacOS Time Machine via the "tmutil" utility.
    An adversary could exclude a path from Time Machine backups to prevent certain files from being backed up.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1490/T1490.md#atomic-test-12---disable-time-machine
    - https://www.loobins.io/binaries/tmutil/
author: Pratinav Chandra
date: 2024-05-29
tags:
    - attack.impact
    - attack.t1490
logsource:
    category: process_creation
    product: macos
detection:
    selection_img:
        - Image|endswith: '/tmutil'
        - CommandLine|contains: 'tmutil'
    selection_cmd:
        CommandLine|contains: 'addexclusion'
    condition: all of selection_*
falsepositives:
    - Legitimate administrator activity
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '/tmutil'
    - CommandLine|contains: 'tmutil'

Stage 2: `selection_cmd`

selection_cmd:
    CommandLine|contains: 'addexclusion'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`addexclusion` `tmutil`	`field:"CommandLine" kind:match`
`Image`	ends_with	`/tmutil`	`field:"Image" kind:ends_with value:"/tmutil"`