Suspicious Browser Child Process - MacOS

Status: test
Severity: medium
Log source: product macos, category process_creation
Author: Sohan G (D4rkCiph3r)
Source: github.com/SigmaHQ/sigma

Detects suspicious child processes spawned from browsers. This could be a result of a potential web browser exploitation.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1189` Drive-by Compromise
Execution	`T1059` Command and Scripting Interpreter, `T1203` Exploitation for Client Execution

Event coverage

Provider	Event	Title
ESF	exec	Process Execution (Notify)

Rule body yaml

title: Suspicious Browser Child Process - MacOS
id: 0250638a-2b28-4541-86fc-ea4c558fa0c6
status: test
description: Detects suspicious child processes spawned from browsers. This could be a result of a potential web browser exploitation.
references:
    - https://fr.slideshare.net/codeblue_jp/cb19-recent-apt-attack-on-crypto-exchange-employees-by-heungsoo-kang
    - https://github.com/elastic/detection-rules/blob/4312d8c9583be524578a14fe6295c3370b9a9307/rules/macos/execution_initial_access_suspicious_browser_childproc.toml
author: Sohan G (D4rkCiph3r)
date: 2023-04-05
tags:
    - attack.initial-access
    - attack.execution
    - attack.t1189
    - attack.t1203
    - attack.t1059
logsource:
    category: process_creation
    product: macos
detection:
    selection:
        ParentImage|contains:
            - 'com.apple.WebKit.WebContent'
            - 'firefox'
            - 'Google Chrome Helper'
            - 'Google Chrome'
            - 'Microsoft Edge'
            - 'Opera'
            - 'Safari'
            - 'Tor Browser'
        Image|endswith:
            - '/bash'
            - '/curl'
            - '/dash'
            - '/ksh'
            - '/osascript'
            - '/perl'
            - '/php'
            - '/pwsh'
            - '/python'
            - '/sh'
            - '/tcsh'
            - '/wget'
            - '/zsh'
    filter_main_generic:
        CommandLine|contains: '--defaults-torrc' # Informs tor to use default config file
    filter_main_ms_autoupdate:
        CommandLine|contains: '/Library/Application Support/Microsoft/MAU*/Microsoft AutoUpdate.app/Contents/MacOS/msupdate' # Microsoft AutoUpdate utility
    filter_main_chrome:
        ParentImage|contains:
            - 'Google Chrome Helper'
            - 'Google Chrome'
        CommandLine|contains:
            - '/Volumes/Google Chrome/Google Chrome.app/Contents/Frameworks/*/Resources/install.sh' # Install the Google Chrome browser
            - '/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_preflight.sh' # Updates the Google Chrome branding configuration files
            - '/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_postflight.sh' # Script that performs the post-installation tasks
    filter_main_ms_edge:
        ParentImage|contains: 'Microsoft Edge'
        CommandLine|contains:
            - 'IOPlatformExpertDevice' # Retrieves the IOPlatformUUID (parent process - Microsoft Edge)
            - 'hw.model' # Retrieves model name of the computer's hardware (parent process - Microsoft Edge)
    filter_main_chromerecovery:
        ParentImage|contains:
            - 'Google Chrome Helper'
            - 'Google Chrome'
        CommandLine|contains|all:
            - '/Users/'
            - '/Library/Application Support/Google/Chrome/recovery/'
            - '/ChromeRecovery'
    filter_optional_null:
        # Aoids alerting for the events which do not have command-line arguments
        CommandLine: null
    filter_optional_empty:
        # Aoids alerting for the events which do not have command-line arguments
        CommandLine: ''
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Legitimate browser install, update and recovery scripts
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_main_* and not 1 of filter_optional_*

Stage 1: `selection`

selection:
    ParentImage|contains:
        - 'com.apple.WebKit.WebContent'
        - 'firefox'
        - 'Google Chrome Helper'
        - 'Google Chrome'
        - 'Microsoft Edge'
        - 'Opera'
        - 'Safari'
        - 'Tor Browser'
    Image|endswith:
        - '/bash'
        - '/curl'
        - '/dash'
        - '/ksh'
        - '/osascript'
        - '/perl'
        - '/php'
        - '/pwsh'
        - '/python'
        - '/sh'
        - '/tcsh'
        - '/wget'
        - '/zsh'

Stage 2: `not filter_main_*`

filter_main_generic:
    CommandLine|contains: '--defaults-torrc'
filter_main_ms_autoupdate:
    CommandLine|contains: '/Library/Application Support/Microsoft/MAU*/Microsoft AutoUpdate.app/Contents/MacOS/msupdate'
filter_main_chrome:
    ParentImage|contains:
        - 'Google Chrome Helper'
        - 'Google Chrome'
    CommandLine|contains:
        - '/Volumes/Google Chrome/Google Chrome.app/Contents/Frameworks/*/Resources/install.sh'
        - '/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_preflight.sh'
        - '/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_postflight.sh'
filter_main_ms_edge:
    ParentImage|contains: 'Microsoft Edge'
    CommandLine|contains:
        - 'IOPlatformExpertDevice'
        - 'hw.model'
filter_main_chromerecovery:
    ParentImage|contains:
        - 'Google Chrome Helper'
        - 'Google Chrome'
    CommandLine|contains|all:
        - '/Users/'
        - '/Library/Application Support/Google/Chrome/recovery/'
        - '/ChromeRecovery'

Stage 3: `not filter_optional_*`

filter_optional_null:
    CommandLine: null
filter_optional_empty:
    CommandLine: ''

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`CommandLine`	match	`/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_postflight.sh`
`CommandLine`	match	`/Applications/Google Chrome.app/Contents/Frameworks/Google Chrome Framework.framework/*/Resources/keystone_promote_preflight.sh`
`CommandLine`	match	`/Volumes/Google Chrome/Google Chrome.app/Contents/Frameworks/*/Resources/install.sh`
`ParentImage`	match	`Google Chrome Helper`
`ParentImage`	match	`Google Chrome`
`CommandLine`	match	`IOPlatformExpertDevice`
`CommandLine`	match	`hw.model`
`ParentImage`	match	`Microsoft Edge`
`ParentImage`	match	`Google Chrome Helper`
`ParentImage`	match	`Google Chrome`
`CommandLine`	match	`/ChromeRecovery`
`CommandLine`	match	`/Library/Application Support/Google/Chrome/recovery/`
`CommandLine`	match	`/Users/`
`CommandLine`	match	`--defaults-torrc`
`CommandLine`	match	`/Library/Application Support/Microsoft/MAU*/Microsoft AutoUpdate.app/Contents/MacOS/msupdate`
`CommandLine`	is_null	(no value, null check)

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
`Image`	ends_with	`/bash` `/curl` `/dash` `/ksh` `/osascript` `/perl` `/php` `/pwsh` `/python` `/sh` `/tcsh` `/wget` `/zsh`
`ParentImage`	match	`Google Chrome` `Google Chrome Helper` `Microsoft Edge` `Opera` `Safari` `Tor Browser` `com.apple.WebKit.WebContent` `firefox`

`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)

Suspicious Browser Child Process - MacOS

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Suspicious Browser Child Process - MacOS

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_main_*

Stage 3: not filter_optional_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_main_*`

Stage 3: `not filter_optional_*`