Detect AppInit DLLs in CrowdStrike LogScale
Adversaries may establish persistence and/or elevate privileges by executing malicious content triggered by AppInit DLLs loaded into processes. Dynamic-link libraries (DLLs) that are specified in the AppInit_DLLs value in the Registry keys HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Windows or HKEY_LOCAL_MACHINE\Software\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll. In practice, this is nearly every desktop process (GUI applications). This Registry-based injection mechanism has been used by multiple APT groups and crimeware families including Flame, FinFisher, and others.
MITRE ATT&CK
- Tactic
- Privilege Escalation Persistence
- Technique
- T1546 Event Triggered Execution
- Sub-technique
- T1546.010 AppInit DLLs
- Canonical reference
- https://attack.mitre.org/techniques/T1546/010/
LogScale Detection Query
#event_simpleName in ("RegGenericValueUpdate", "AsepValueUpdate", "RegStringValueUpdate")
| RegObjectName = /(?i)(SOFTWARE\\(Wow6432Node\\)?Microsoft\\Windows NT\\CurrentVersion\\Windows)$/
| RegValueName = /(?i)^(AppInit_DLLs|LoadAppInit_DLLs|RequireSignedAppInit_DLLs)$/
| case {
RegValueName = /(?i)^AppInit_DLLs$/
AND NOT RegStringValue = /(?i)(system32|syswow64)/
AND RegStringValue != ""
| DetectionType := "APPINIT_SUSPICIOUS_DLL_PATH" ;
RegValueName = /(?i)^LoadAppInit_DLLs$/ AND RegStringValue = "1"
| DetectionType := "APPINIT_LOADING_ENABLED" ;
RegValueName = /(?i)^RequireSignedAppInit_DLLs$/ AND RegStringValue = "0"
| DetectionType := "APPINIT_SIGNATURE_DISABLED" ;
*
| DetectionType := "APPINIT_KEY_MODIFIED"
}
| table([timestamp, ComputerName, UserName, DetectionType, RegObjectName, RegValueName, RegStringValue, FileName, CommandLine])
| sort(timestamp, order=desc)Detects T1546.010 AppInit DLL persistence by monitoring CrowdStrike Falcon registry write events for modifications to AppInit_DLLs registry keys. Classifies events into four detection types: suspicious non-system DLL paths, enabling AppInit loading, disabling signature enforcement, and general key modification. Covers both RegGenericValueUpdate and AsepValueUpdate Falcon event types.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike or other EDR vendor sensor updates that temporarily modify AppInit_DLLs-adjacent registry areas during kernel hook management — filter by known vendor process hashes
- Windows in-place upgrade or feature update processes that re-write CurrentVersion registry keys including AppInit_DLLs as part of Windows component servicing
- Legitimate pen testing or red team exercises conducted by internal security teams — correlate with change management tickets and authorized testing windows
Other platforms for T1546.010
Testing Methodology
Validate this detection against 3 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Register DLL in AppInit_DLLs and Enable Loading
Expected signal: Three Sysmon Event ID 13 records: (1) AppInit_DLLs set to C:\Users\Public\argus_appinit.dll, (2) LoadAppInit_DLLs set to 1, (3) RequireSignedAppInit_DLLs set to 0. The combination of all three changes in a short time window is a high-confidence indicator.
- Test 2Enable AppInit Loading Without DLL Path
Expected signal: Sysmon Event ID 13: TargetObject contains Windows NT\CurrentVersion\Windows\LoadAppInit_DLLs, Details=1. This single-value change is an intermediate persistence indicator.
- Test 3Audit Current AppInit_DLLs State
Expected signal: Process creation for reg.exe (multiple times) querying AppInit keys. Read-only — no modifications. Use this as a scheduled hunt query to detect pre-existing AppInit DLL registrations.
References (5)
- https://attack.mitre.org/techniques/T1546/010/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1546.010/T1546.010.md
- https://support.microsoft.com/en-us/topic/description-of-the-appinit-dlls-feature-in-windows-7-and-windows-server-2008-r2-aabbf40f-3e10-eadd-6260-79df3d753b5f
- https://www.mandiant.com/resources/blog/likely-iranian-threat-actor-conducts-politically-motivated-disruptive-activity-against-israel
- https://pentestlab.blog/2019/12/12/persistence-appinit-dlls/
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