Windows AppCertDLL Modification Via Registry

Name:Windows AppCertDLL Modification Via Registry
id:547d98dd-6d6e-4aa4-be91-a1a119f48df3
version:1
date:None
author:Nasreddine Bencherchali, Splunk
status:production
type:Anomaly
Description:This analytic detects attempts to modify AppCertDLL registry entries. Values under this registry entry 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.
Data_source:

• -Sysmon EventID 13

search:| tstats `security_content_summariesonly`
count min(_time) as firstTime
max(_time) as lastTime

FROM datamodel=Endpoint.Registry WHERE

Registry.action = "modified"
Registry.registry_path= "*\\Control\\Session Manager\\AppCertDLLs\\*"
Registry.registry_value_data = "*"

by Registry.action Registry.dest Registry.process_guid Registry.process_id
Registry.registry_hive Registry.registry_path Registry.registry_key_name
Registry.registry_value_data Registry.registry_value_name
Registry.registry_value_type Registry.status
Registry.user Registry.vendor_product

| `drop_dm_object_name(Registry)`
| where isnotnull(registry_value_data)
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `windows_appcertdll_modification_via_registry_filter`

how_to_implement:To successfully implement this search, you need to be ingesting logs with the registry value name, registry path, and registry value data from your endpoints. If you are using Sysmon, you must have at least version 2.0 of the official Sysmon TA. https://splunkbase.splunk.com/app/5709
known_false_positives:Modifications to AppCertDLL entries may be made by legitimate software updates or trusted system management tools. Review changes to ensure they are from approved sources.
References:
  -https://www.hexacorn.com/blog/2013/01/19/beyond-good-ol-run-key-part-3/
drilldown_searches:
 name:'View the detection results for - "$dest$"'
 search:'%original_detection_search% | search dest = "$dest$"'
 earliest_offset:'$info_min_time$'
 latest_offset:'$info_max_time$'
 name:'View risk events for the last 7 days for - "$dest$"'
 search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | 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'
analytic_story:['Windows Persistence Techniques', 'Windows Privilege Escalation']

asset_type:Endpoint

mitre_attack_id:['T1546.009']

product:['Splunk Enterprise', 'Splunk Enterprise Security', 'Splunk Cloud']

category:endpoint

security_domain:endpoint

tags:

tests:
 name:'True Positive Test'
 attack_data:
  data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1546.009/snapattack/registry.log
  source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
  sourcetype: XmlWinEventLog
 test_type:'unit'
manual_test:None