Shell32 DLL Execution in Suspicious Directory

Severity: high
Author: Christian Burkard (Nextron Systems)
Source: upstream

Detects shell32.dll executing a DLL in a suspicious directory

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218.011` System Binary Proxy Execution: Rundll32

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\rundll32.exe'
OriginalFileName: RUNDLL32.EXE

Stage 2: `all of selection_cli`

or:
CommandLine|contains: '%AppData%'
CommandLine|contains: '%LocalAppData%'
CommandLine|contains: '%Temp%'
CommandLine|contains: '%tmp%'
CommandLine|contains: '\AppData\'
CommandLine|contains: '\Temp\'
CommandLine|contains: '\Users\Public\'
CommandLine|contains: Control_RunDLL
CommandLine|contains: shell32.dll

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
`CommandLine`	match	`%AppData%` corpus 7 (sigma 7) `%LocalAppData%` `%Temp%` corpus 4 (sigma 4) `%tmp%` corpus 9 (sigma 9) `Control_RunDLL` corpus 2 (sigma 2) `\AppData\` corpus 8 (sigma 8) `\Temp\` corpus 7 (sigma 7) `\Users\Public\` corpus 17 (sigma 17) `shell32.dll` corpus 2 (sigma 2)
`Image`	ends_with	`\rundll32.exe` corpus 76 (sigma 76)
`OriginalFileName`	eq	`RUNDLL32.EXE` corpus 28 (sigma 25, splunk 3)