Uncommon Assistive Technology Applications Execution Via AtBroker.EXE

Status: test
Severity: medium
Log source: product windows, category process_creation
Author: Mateusz Wydra, oscd.community
Source: github.com/SigmaHQ/sigma

Detects the start of a non built-in assistive technology applications via "Atbroker.EXE".

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation

Rule body yaml

title: Uncommon  Assistive Technology Applications Execution Via AtBroker.EXE
id: f24bcaea-0cd1-11eb-adc1-0242ac120002
status: test
description: Detects the start of a non built-in assistive technology applications via "Atbroker.EXE".
references:
    - http://www.hexacorn.com/blog/2016/07/22/beyond-good-ol-run-key-part-42/
    - https://lolbas-project.github.io/lolbas/Binaries/Atbroker/
author: Mateusz Wydra, oscd.community
date: 2020-10-12
modified: 2024-03-06
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\AtBroker.exe'
        - OriginalFileName: 'AtBroker.exe'
    selection_cli:
        CommandLine|contains: 'start'
    filter_main_builtin:
        CommandLine|contains:
            - 'animations'
            - 'audiodescription'
            - 'caretbrowsing'
            - 'caretwidth'
            - 'colorfiltering'
            - 'cursorindicator'
            - 'cursorscheme'
            - 'filterkeys'
            - 'focusborderheight'
            - 'focusborderwidth'
            - 'highcontrast'
            - 'keyboardcues'
            - 'keyboardpref'
            - 'livecaptions'
            - 'magnifierpane'
            - 'messageduration'
            - 'minimumhitradius'
            - 'mousekeys'
            - 'Narrator'
            - 'osk'
            - 'overlappedcontent'
            - 'showsounds'
            - 'soundsentry'
            - 'speechreco'
            - 'stickykeys'
            - 'togglekeys'
            - 'voiceaccess'
            - 'windowarranging'
            - 'windowtracking'
            - 'windowtrackingtimeout'
            - 'windowtrackingzorder'
    filter_optional_java:
        CommandLine|contains: 'Oracle_JavaAccessBridge'
    condition: all of selection_* and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Legitimate, non-default assistive technology applications execution
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_* and not 1 of filter_main_* and not 1 of filter_optional_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\AtBroker.exe'
    - OriginalFileName: 'AtBroker.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains: 'start'

Stage 3: `not filter_main_builtin`

filter_main_builtin:
    CommandLine|contains:
        - 'animations'
        - 'audiodescription'
        - 'caretbrowsing'
        - 'caretwidth'
        - 'colorfiltering'
        - 'cursorindicator'
        - 'cursorscheme'
        - 'filterkeys'
        - 'focusborderheight'
        - 'focusborderwidth'
        - 'highcontrast'
        - 'keyboardcues'
        - 'keyboardpref'
        - 'livecaptions'
        - 'magnifierpane'
        - 'messageduration'
        - 'minimumhitradius'
        - 'mousekeys'
        - 'Narrator'
        - 'osk'
        - 'overlappedcontent'
        - 'showsounds'
        - 'soundsentry'
        - 'speechreco'
        - 'stickykeys'
        - 'togglekeys'
        - 'voiceaccess'
        - 'windowarranging'
        - 'windowtracking'
        - 'windowtrackingtimeout'
        - 'windowtrackingzorder'

Stage 4: `not filter_optional_java`

filter_optional_java:
    CommandLine|contains: 'Oracle_JavaAccessBridge'

Exclusions

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

Field	Kind	Excluded values
`CommandLine`	match	`Narrator`
`CommandLine`	match	`animations`
`CommandLine`	match	`audiodescription`
`CommandLine`	match	`caretbrowsing`
`CommandLine`	match	`caretwidth`
`CommandLine`	match	`colorfiltering`
`CommandLine`	match	`cursorindicator`
`CommandLine`	match	`cursorscheme`
`CommandLine`	match	`filterkeys`
`CommandLine`	match	`focusborderheight`
`CommandLine`	match	`focusborderwidth`
`CommandLine`	match	`highcontrast`
`CommandLine`	match	`keyboardcues`
`CommandLine`	match	`keyboardpref`
`CommandLine`	match	`livecaptions`
`CommandLine`	match	`magnifierpane`
`CommandLine`	match	`messageduration`
`CommandLine`	match	`minimumhitradius`
`CommandLine`	match	`mousekeys`
`CommandLine`	match	`osk`
`CommandLine`	match	`overlappedcontent`
`CommandLine`	match	`showsounds`
`CommandLine`	match	`soundsentry`
`CommandLine`	match	`speechreco`
`CommandLine`	match	`stickykeys`
`CommandLine`	match	`togglekeys`
`CommandLine`	match	`voiceaccess`
`CommandLine`	match	`windowarranging`
`CommandLine`	match	`windowtracking`
`CommandLine`	match	`windowtrackingtimeout`
`CommandLine`	match	`windowtrackingzorder`
`CommandLine`	match	`Oracle_JavaAccessBridge`

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	`start` corpus 13 (sigma 11, splunk 2)
`Image`	ends_with	`\AtBroker.exe` corpus 2 (sigma 2)
`OriginalFileName`	eq	`AtBroker.exe`

`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)

Uncommon Assistive Technology Applications Execution Via AtBroker.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Stage 3: `not filter_main_builtin`

Stage 4: `not filter_optional_java`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Uncommon Assistive Technology Applications Execution Via AtBroker.EXE

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Stage 3: not filter_main_builtin

Stage 4: not filter_optional_java

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`

Stage 3: `not filter_main_builtin`

Stage 4: `not filter_optional_java`