Windows AppCertDLL Modification Via Registry

name: Windows AppCertDLL Modification Via Registry
id: 547d98dd-6d6e-4aa4-be91-a1a119f48df3
version: 1
creation_date: '2026-07-27'
modification_date: '2026-07-27'
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"
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Potential AppCertDLL modification with value [$registry_value_data$] activity observed on [$dest$]
threat_objects:
    - field: registry_value_data
      type: registry_value_text
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
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