Atbroker Registry Change

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

Detects creation/modification of Assistive Technology applications and persistence with usage of 'at'

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1547` Boot or Logon Autostart Execution
Privilege Escalation	`T1547` Boot or Logon Autostart Execution
Stealth	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event	Title
Sysmon	Event ID 12	RegistryEvent (Object create and delete)
Sysmon	Event ID 13	RegistryEvent (Value Set)
Sysmon	Event ID 14	RegistryEvent (Key and Value Rename)

Rule body yaml

title: Atbroker Registry Change
id: 9577edbb-851f-4243-8c91-1d5b50c1a39b
status: test
description: Detects creation/modification of Assistive Technology applications and persistence with usage of 'at'
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: 2020-10-13
modified: 2023-01-19
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1218
    - attack.persistence
    - attack.t1547
logsource:
    category: registry_event
    product: windows
detection:
    selection:
        TargetObject|contains:
            - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'
            - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'
    filter_atbroker:
        Image: 'C:\Windows\system32\atbroker.exe'
        TargetObject|contains: '\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'
        Details: '(Empty)'
    filter_uninstallers:
        Image|startswith: 'C:\Windows\Installer\MSI'
        TargetObject|contains: 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'
    condition: selection and not 1 of filter_*
falsepositives:
    - Creation of non-default, legitimate at usage
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not 1 of filter_*

Stage 1: `selection`

selection:
    TargetObject|contains:
        - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'
        - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'

Stage 2: `not filter_*`

filter_atbroker:
    Image: 'C:\Windows\system32\atbroker.exe'
    TargetObject|contains: '\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'
    Details: '(Empty)'
filter_uninstallers:
    Image|startswith: 'C:\Windows\Installer\MSI'
    TargetObject|contains: 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'

Exclusions

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

Field	Kind	Excluded values
`Details`	eq	`(Empty)`
`Image`	eq	`C:\Windows\system32\atbroker.exe`
`TargetObject`	match	`\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration`
`Image`	starts_with	`C:\Windows\Installer\MSI`
`TargetObject`	match	`Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs`

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
`TargetObject`	match	`Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs` `Software\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration`

`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)

Atbroker Registry Change

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_*`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Atbroker Registry Change

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: not filter_*

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `not filter_*`