macOS Screen Sharing Session

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

Detects screen sharing session attachment and detachment events. Screen sharing can be used for legitimate remote administration or by attackers for initial access and lateral movement. Monitor for unexpected or unauthorized sessions.

MITRE ATT&CK coverage

Tactic	Techniques
Lateral Movement	`T1021.005` Remote Services: VNC, `T1563` Remote Service Session Hijacking

Rule body yaml

title: macOS Screen Sharing Session
id: 1684f3e3-d701-477f-be1b-7169dba38f91
status: experimental
description: 'Detects screen sharing session attachment and detachment events. Screen
  sharing

  can be used for legitimate remote administration or by attackers for initial

  access and lateral movement. Monitor for unexpected or unauthorized sessions.

  '
author: Eric Brown - Nebulock, Inc.
date: 2025/10/31
modified: 2025/10/31
references:
- https://attack.mitre.org/techniques/T1021/005/
- https://attack.mitre.org/techniques/T1563/
logsource:
  product: macos
  service: endpointsecurity
detection:
  selection_attach:
    esf.event_type: 135
    event.action: screensharing_attach
  selection_detach:
    esf.event_type: 136
    event.action: screensharing_detach
  condition: selection_attach or selection_detach
falsepositives:
- Legitimate IT support and remote administration
- User-initiated screen sharing for collaboration
- Automated management tools
fields:
- event_type
- event_name
- User
- source_ip
- session_id
tags:
- attack.initial_access
- attack.t1021.005
- attack.lateral_movement
- attack.t1563
level: medium

Stages and Predicates

Stage 0: `condition`

selection_attach or selection_detach

Stage 1: `selection_attach`

selection_attach:
  esf.event_type: 135
  event.action: screensharing_attach

Stage 2: `selection_detach`

selection_detach:
  esf.event_type: 136
  event.action: screensharing_detach

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
`esf.event_type`	eq	`135` `136`
`event.action`	eq	`screensharing_attach` `screensharing_detach`

`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 Screen Sharing Session

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_attach`

Stage 2: `selection_detach`

Indicators

Keyboard shortcuts

Search operators

macOS Screen Sharing Session

MITRE ATT&CK coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_attach

Stage 2: selection_detach

Indicators

Stage 0: `condition`

Stage 1: `selection_attach`

Stage 2: `selection_detach`