New DLL Added to AppInit_DLLs Registry Key

Severity: medium
Author: Ilyas Ochkov, oscd.community, Tim Shelton
Source: upstream

DLLs that are specified in the AppInit_DLLs value in the Registry key HKLM\Software\Microsoft\Windows NT\CurrentVersion\Windows are loaded by user32.dll into every process that loads user32.dll

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1546.010` Event Triggered Execution: AppInit DLLs
Privilege Escalation	`T1546.010` Event Triggered Execution: AppInit DLLs

Event coverage

Provider	Event ID	Title
Sysmon	12	RegistryEvent (Object create and delete)
Sysmon	13	RegistryEvent (Value Set)
Sysmon	14	RegistryEvent (Key and Value Rename)

Stages and Predicates

Stage 1: `selection`

or:
NewName|endswith: '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
NewName|endswith: '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
TargetObject|endswith: '\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'
TargetObject|endswith: '\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls'

Stage 2: `not filter`

Details: '(Empty)'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Details`	eq	`(Empty)` corpus 24 (sigma 24)
`NewName`	ends_with	`\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls` `\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls`
`TargetObject`	ends_with	`\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls` `\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Windows\AppInit_Dlls`