Windows AD GPO New CSE Addition

Status: production
Severity: medium
Group by: LogonId, ObjectClass, ObjectDN, OpCorrelationID, user
Author: Dean Luxton
Source: github.com/splunk/security_content

This detection identifies when a a new client side extension is added to an Active Directory Group Policy using the Group Policy Management Console.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1484.001` Domain or Tenant Policy Modification: Group Policy Modification
Defense Impairment	`T1222.001` File and Directory Permissions Modification: Windows Permissions, `T1484.001` Domain or Tenant Policy Modification: Group Policy Modification

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 5136	A directory service object was modified.

Rule body splunk

name: Windows AD GPO New CSE Addition
id: 700c11d1-da09-47b2-81aa-358c143c7986
version: 10
creation_date: '2024-07-01'
modification_date: '2026-05-13'
author: Dean Luxton
status: production
type: TTP
description: This detection identifies when a a new client side extension is added to an Active Directory Group Policy using the Group Policy Management Console.
data_source:
    - Windows Event Log Security 5136
search: |-
    `wineventlog_security` EventCode=5136 ObjectClass=groupPolicyContainer AttributeLDAPDisplayName=gPCMachineExtensionNames
      | stats min(_time) as _time values(eval(if(OperationType=="%%14675",AttributeValue,null))) as old_value values(eval(if(OperationType=="%%14674",AttributeValue,null))) as new_value values(OperationType) as OperationType values(dest) as dest
        BY ObjectClass ObjectDN OpCorrelationID
           src_user SubjectLogonId
      | rex field=old_value max_match=10000 "(?P<old_values>\{.*?\})"
      | rex field=new_value max_match=10000 "(?P<new_values>\{.*?\})"
      | rex field=ObjectDN max_match=10000 "CN=(?P<policy_guid>\{.*?\})"
      | mvexpand new_values
      | where NOT new_values IN (old_values,"{00000000-0000-0000-0000-000000000000}",policy_guid) AND match(new_values, "^\{[A-Z
      | \d]+\-[A-Z
      | \d]+\-[A-Z
      | \d]+\-[A-Z
      | \d]+\-[A-Z
      | \d]+\}")
      | lookup msad_guid_lookup guid as new_values OUTPUTNEW displayName as policyType
      | eval newPolicy=if(policyType like "%",policyType,new_values)
      | join ObjectDN  [
      | search `admon` objectCategory="CN=Group-Policy-Container*" admonEventType=Update
      | stats latest(displayName) as displayName
        BY distinguishedName
      | eval ObjectDN=upper(distinguishedName)]
      | stats values(OpCorrelationID) as OpCorrelationID values(src_user) as src_user values(SubjectLogonId) as SubjectLogonId values(newPolicy) as newPolicy values(displayName) as policyName
        BY ObjectDN
      | `windows_ad_gpo_new_cse_addition_filter`
how_to_implement: Ensure you are ingesting Active Directory audit logs - specifically event 5136, admon data is also used to display the display name of the GPO. See lantern article in references for further on how to onboard AD audit data. Ensure the wineventlog_security and admon macros are configured with the correct indexes.
known_false_positives: General usage of group policy will trigger this detection, also please not GPOs modified using tools such as SharpGPOAbuse will not generate the AD audit events which enable this detection.
references:
    - https://wald0.com/?p=179
    - https://learn.microsoft.com/en-gb/archive/blogs/mempson/group-policy-client-side-extension-list
    - https://lantern.splunk.com/Security/Product_Tips/Enterprise_Security/Enabling_an_audit_trail_from_Active_Directory
    - https://github.com/FSecureLABS/SharpGPOAbuse
drilldown_searches:
    - name: View the detection results for - "$src_user$"
      search: '%original_detection_search% | search  src_user = "$src_user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$src_user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$src_user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
finding:
    title: $src_user$ has added new GPO Client Side Extensions $newPolicy$ to the policy $policyName$
    entity:
        field: src_user
        type: user
        score: 50
analytic_story:
    - Sneaky Active Directory Persistence Tricks
asset_type: Endpoint
mitre_attack_id:
    - T1222.001
    - T1484.001
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1484.001/group_policy_new_cse/windows-security.log
          source: XmlWinEventLog:Security
          sourcetype: XmlWinEventLog
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1484.001/group_policy_new_cse/windows-admon.log
          source: ActiveDirectory
          sourcetype: ActiveDirectory
      test_type: unit

Stages and Predicates

Stage 1: `search`

`wineventlog_security` EventCode=5136 ObjectClass=groupPolicyContainer AttributeLDAPDisplayName=gPCMachineExtensionNames

Stage 2: `stats`

| stats min(_time) as _time values(eval(if(OperationType=="%%14675",AttributeValue,null))) as old_value values(eval(if(OperationType=="%%14674",AttributeValue,null))) as new_value values(OperationType) as OperationType values(dest) as dest
    BY ObjectClass ObjectDN OpCorrelationID
       src_user SubjectLogonId

Stage 3: `rex`

| rex field=old_value max_match=10000 "(?P<old_values>\{.*?\})"

Stage 4: `rex`

| rex field=new_value max_match=10000 "(?P<new_values>\{.*?\})"

Stage 5: `rex`

| rex field=ObjectDN max_match=10000 "CN=(?P<policy_guid>\{.*?\})"

Stage 6: `mvexpand`

| mvexpand new_values

Stage 7: `where`

| where NOT new_values IN (old_values,"{00000000-0000-0000-0000-000000000000}",policy_guid) AND match(new_values, "^\{[A-Z
  | \d]+\-[A-Z
  | \d]+\-[A-Z
  | \d]+\-[A-Z
  | \d]+\-[A-Z
  | \d]+\}")

Stage 8: `lookup`

| lookup msad_guid_lookup guid as new_values OUTPUTNEW displayName as policyType

Lookup table: msad_guid_lookup
Key field: guid as new_values
Output columns: ['displayName', 'policyType']

Stage 9: `eval`

| eval newPolicy=if(policyType like "%",policyType,new_values)

newPolicy =

iflike(policyType, "%")policyType

elsenew_values

Stage 10: `join`

| join ObjectDN  [
  | search `admon` objectCategory="CN=Group-Policy-Container*" admonEventType=Update
  | stats latest(displayName) as displayName
    BY distinguishedName
  | eval ObjectDN=upper(distinguishedName)]

Stage 11: `stats`

| stats values(OpCorrelationID) as OpCorrelationID values(src_user) as src_user values(SubjectLogonId) as SubjectLogonId values(newPolicy) as newPolicy values(displayName) as policyName
    BY ObjectDN

Stage 12: `search`

| `windows_ad_gpo_new_cse_addition_filter`

Exclusions

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

Field	Kind	Excluded values
`new_values`	in	`"{00000000-0000-0000-0000-000000000000}"`, `old_values`, `policy_guid`

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
`AttributeLDAPDisplayName`	eq	`gPCMachineExtensionNames` corpus 7 (sigma 3, elastic 3, splunk 1)
`EventCode`	eq	`5136` corpus 30 (splunk 24, kusto 5, elastic 1)
`ObjectClass`	eq	`groupPolicyContainer` corpus 6 (sigma 3, splunk 3)
`admonEventType`	eq	`Update` corpus 5 (splunk 5)
`new_values`	match	`"^\{[A-Z \| \d]+\-[A-Z \| \d]+\-[A-Z \| \d]+\-[A-Z \| \d]+\-[A-Z \| \d]+\}"`
`objectCategory`	eq	`"CN=Group-Policy-Container*"` corpus 3 (splunk 3)

`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)

Windows AD GPO New CSE Addition

MITRE ATT&CK coverage

Event coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `stats`

Stage 3: `rex`

Stage 4: `rex`

Stage 5: `rex`

Stage 6: `mvexpand`

Stage 7: `where`

Stage 8: `lookup`

Stage 9: `eval`

Stage 10: `join`

Stage 11: `stats`

Stage 12: `search`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Windows AD GPO New CSE Addition

MITRE ATT&CK coverage

Event coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: stats

Stage 3: rex

Stage 4: rex

Stage 5: rex

Stage 6: mvexpand

Stage 7: where

Stage 8: lookup

Stage 9: eval

Stage 10: join

Stage 11: stats

Stage 12: search

Exclusions

Indicators

Stage 1: `search`

Stage 2: `stats`

Stage 3: `rex`

Stage 4: `rex`

Stage 5: `rex`

Stage 6: `mvexpand`

Stage 7: `where`

Stage 8: `lookup`

Stage 9: `eval`

Stage 10: `join`

Stage 11: `stats`

Stage 12: `search`