Startup/Logon Script added to Group Policy Object

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Startup/Logon Script added to Group Policy Object

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Detects the modification of Group Policy Objects (GPO) to add a startup/logon script to users or computer objects.

Rule type: query

Rule indices:

winlogbeat-*
logs-system.*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: None (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Elastic
Host
Windows
Threat Detection
Privilege Escalation
Active Directory

Version: 4

Rule authors:

Elastic

Rule license: Elastic License v2

Investigation guide

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## Triage and analysis

### Investigating Scheduled Task Execution at Scale via GPO

Group Policy Objects (GPOs) can be used by attackers to instruct arbitrarily large groups of
clients to execute specified commands at startup, logon, shutdown, and logoff. This is done by creating or modifying the
`scripts.ini` or `psscripts.ini` files. The scripts are stored in the following path: `<GPOPath>\Machine\Scripts\`,
`<GPOPath>\User\Scripts\`

#### Possible investigation steps

- This attack abuses a legitimate mechanism of Active Directory, so it is important to determine whether the activity
is legitimate and the administrator is authorized to perform this operation.
- Retrieve the contents of the `ScheduledTasks.xml` file, and check the `<Command>` and `<Arguments>` XML tags for any
potentially malicious commands or binaries.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Scope which objects may be compromised by retrieving information about which objects are controlled by the GPO.

### False positive analysis

- Verify if the execution is legitimately authorized and executed under a change management process.

### Related rules

- Group Policy Abuse for Privilege Addition - b9554892-5e0e-424b-83a0-5aef95aa43bf
- Scheduled Task Execution at Scale via GPO - 15a8ba77-1c13-4274-88fe-6bd14133861e

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- The investigation and containment must be performed in every computer controlled by the GPO, where necessary.
- Remove the script from the GPO.
- Check if other GPOs have suspicious scripts attached.
- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
- Using the incident response data, update logging and audit policies to improve the mean time to detect (MTTD) and the
mean time to respond (MTTR).

## Config

The 'Audit Detailed File Share' audit policy must be configured (Success Failure).
Steps to implement the logging policy with with Advanced Audit Configuration:

```
Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
Object Access >
Audit Detailed File Share (Success,Failure)
```

The 'Audit Directory Service Changes' audit policy must be configured (Success Failure).
Steps to implement the logging policy with with Advanced Audit Configuration:

```
Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
DS Access >
Audit Directory Service Changes (Success,Failure)
```

Rule query

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(
 event.code:5136 and winlog.event_data.AttributeLDAPDisplayName:(gPCMachineExtensionNames or gPCUserExtensionNames) and
   winlog.event_data.AttributeValue:(*42B5FAAE-6536-11D2-AE5A-0000F87571E3* and
                                      (*40B66650-4972-11D1-A7CA-0000F87571E3* or *40B6664F-4972-11D1-A7CA-0000F87571E3*))
)
or
(
 event.code:5145 and winlog.event_data.ShareName:\\\\*\\SYSVOL and
   winlog.event_data.RelativeTargetName:(*\\scripts.ini or *\\psscripts.ini) and
   (message:WriteData or winlog.event_data.AccessList:*%%4417*)
)

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Privilege Escalation
- ID: TA0004
- Reference URL: https://attack.mitre.org/tactics/TA0004/
Technique:
- Name: Boot or Logon Autostart Execution
- ID: T1547
- Reference URL: https://attack.mitre.org/techniques/T1547/
Technique:
- Name: Domain Policy Modification
- ID: T1484
- Reference URL: https://attack.mitre.org/techniques/T1484/
Sub-technique:
- Name: Group Policy Modification
- ID: T1484.001
- Reference URL: https://attack.mitre.org/techniques/T1484/001/

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