macOS Encryption Tool Usage

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

Detects execution of encryption tools (openssl, gpg, diskutil) which may indicate ransomware activity or data encryption for impact. Adversaries encrypt data to deny availability and extort victims. Also monitors disk encryption operations.

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1486` Data Encrypted for Impact, `T1565.001` Data Manipulation: Stored Data Manipulation

Rule body yaml

title: macOS Encryption Tool Usage
id: f2a3b4c5-d6e7-4f8a-9b0c-1d2e3f4a5b6c
status: experimental
description: 'Detects execution of encryption tools (openssl, gpg, diskutil) which
  may indicate

  ransomware activity or data encryption for impact. Adversaries encrypt data to

  deny availability and extort victims. Also monitors disk encryption operations.

  '
author: Eric Brown - Nebulock, Inc.
date: 2025/10/31
modified: 2025/10/31
references:
- https://attack.mitre.org/techniques/T1486/
- https://attack.mitre.org/techniques/T1565/001/
logsource:
  product: macos
  service: endpointsecurity
detection:
  selection_event:
    esf.event_type: 9
    event.action: exec
  selection_process:
    Image|endswith:
    - /openssl
    - /gpg
    - /gpg2
    - /diskutil
  selection_encryption:
    CommandLine|contains:
    - 'enc '
    - encrypt
    - aes
    - --cipher
    - apfs encryptVolume
    - coreStorage convert
  condition: selection_event and selection_process and selection_encryption
falsepositives:
- Legitimate data encryption for security
- FileVault and disk encryption setup
- Secure file transfer preparations
- Development and testing of encryption features
fields:
- Image
- CommandLine
- ProcessId
- ParentProcessId
- User
tags:
- attack.impact
- attack.t1486
- attack.t1565.001
level: medium

Stages and Predicates

Stage 0: `condition`

selection_event and selection_process and selection_encryption

Stage 1: `selection_event`

selection_event:
  esf.event_type: 9
  event.action: exec

Stage 2: `selection_process`

selection_process:
  Image|endswith:
  - /openssl
  - /gpg
  - /gpg2
  - /diskutil

Stage 3: `selection_encryption`

selection_encryption:
  CommandLine|contains:
  - 'enc '
  - encrypt
  - aes
  - --cipher
  - apfs encryptVolume
  - coreStorage convert

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`CommandLine`	match	`--cipher` `aes` `apfs encryptVolume` `coreStorage convert` `enc` `encrypt`
`Image`	ends_with	`/diskutil` `/gpg` `/gpg2` `/openssl`
`esf.event_type`	eq	`9`
`event.action`	eq	`exec`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

macOS Encryption Tool Usage

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_event`

Stage 2: `selection_process`

Stage 3: `selection_encryption`

Indicators

Keyboard shortcuts

Search operators

macOS Encryption Tool Usage

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_event

Stage 2: selection_process

Stage 3: selection_encryption

Indicators

Stage 0: `condition`

Stage 1: `selection_event`

Stage 2: `selection_process`

Stage 3: `selection_encryption`