Detection: Windows AppCertDLL Modification Via Command Line

Description

This analytic detects attempts to modify AppCertDLL registry keys via some command line utility. Values under this key are used to specify DLLs loaded by the Windows Session Manager. Such modifications can be abused by attackers to load malicious code early in the system startup process, enabling persistent malware execution with high privileges. If confirmed malicious, this behavior may lead to system compromise, persistence, and the evasion of security controls.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8Processes.process="*\\Control\\Session Manager\\AppCertDLLs*"
 9
10by Processes.process Processes.vendor_product Processes.user_id
11   Processes.process_hash Processes.parent_process_name
12   Processes.parent_process_exec Processes.action Processes.dest
13   Processes.process_current_directory Processes.process_path
14   Processes.process_integrity_level Processes.original_file_name
15   Processes.parent_process Processes.parent_process_path
16   Processes.parent_process_guid Processes.parent_process_id
17   Processes.process_guid Processes.process_id
18   Processes.user Processes.process_name
19
20
21| `drop_dm_object_name(Processes)`
22
23| `security_content_ctime(firstTime)`
24
25| `security_content_ctime(lastTime)`
26
27| `windows_appcertdll_modification_via_command_line_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'XmlWinEventLog'	'XmlWinEventLog:Security'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Modifications to AppCertDLL keys may be made by legitimate software updates or trusted system management tools. Review changes to ensure they are from approved sources.

Associated Analytic Story

• Windows Persistence Techniques

• Windows Privilege Escalation

Risk Based Analytics (RBA)

Risk Message:

Potential AppCertDLL modification activity observed on $dest$ via $process$.

Detection Testing

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 1