Detect Rundll32 in Splunk
Adversaries may abuse rundll32.exe to proxy execution of malicious code. Using rundll32.exe avoids triggering security tools that allowlist it or ignore it due to high noise. Rundll32 can execute DLL payloads, Control Panel items (.cpl via Control_RunDLL), JavaScript (via mshtml,RunHTMLApplication), remote COM scriptlets, and system DLLs (zipfldr.dll, ieframe.dll). Adversaries may also export DLL functions by ordinal number or obscure function names by appending W/A character set suffixes. Widely used by InvisiMole, Latrodectus, FIN8, APT28, BoomBox, MegaCortex, QakBot, Emotet, Cobalt Strike, and many ransomware families.
MITRE ATT&CK
- Tactic
- Defense Evasion
- Technique
- T1218 System Binary Proxy Execution
- Sub-technique
- T1218.011 Rundll32
- Canonical reference
- https://attack.mitre.org/techniques/T1218/011/
SPL Detection Query
index=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=1
(Image="*\\rundll32.exe" OR ParentImage="*\\rundll32.exe")
| eval JavaScriptExec=if(match(CommandLine, "(javascript:|mshtml|RunHTMLApplication)"), 1, 0)
| eval RemoteSCT=if(match(CommandLine, "(http[s]?://|GetObject\()"), 1, 0)
| eval MiniDump=if(match(CommandLine, "MiniDump"), 1, 0)
| eval ControlPanel=if(match(CommandLine, "(Control_RunDLL|\.cpl)"), 1, 0)
| eval SuspiciousPath=if(match(CommandLine, "(Temp|AppData|Downloads|Public|Desktop)"), 1, 0)
| eval OrdinalLoad=if(match(CommandLine, ",#[0-9]+"), 1, 0)
| eval OfficeParent=if(match(ParentImage, "(winword|excel|outlook|powerpnt)\.exe"), 1, 0)
| eval ScriptParent=if(match(ParentImage, "(cmd|powershell|wscript|cscript|mshta)\.exe"), 1, 0)
| eval SuspiciousChild=if((ParentImage="*\\rundll32.exe") AND match(Image, "(cmd|powershell|wscript|cscript|net|certutil)\.exe"), 1, 0)
| eval RiskScore=JavaScriptExec + RemoteSCT + MiniDump + (SuspiciousPath * (OfficeParent + ScriptParent)) + OrdinalLoad + OfficeParent + SuspiciousChild
| where RiskScore > 0 OR SuspiciousChild=1
| table _time, host, User, Image, CommandLine, ParentImage, ParentCommandLine, JavaScriptExec, RemoteSCT, MiniDump, ControlPanel, SuspiciousPath, OrdinalLoad, OfficeParent, ScriptParent, SuspiciousChild, RiskScore
| sort - _timeDetects rundll32.exe abuse using Sysmon Event ID 1. JavaScript execution, remote SCT loading, and MiniDump (LSASS dump) score unconditionally as these are high-confidence indicators. Suspicious path only scores when combined with Office or scripting parents. Ordinal-based loading and child processes are additional risk indicators.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate software using rundll32.exe to load and execute DLL functions from Program Files
- Windows system functions using rundll32.exe for Control Panel applets and shell extensions
- Software deployment tools using rundll32.exe to trigger installation DLL entry points
- Security tools and EDR agents using rundll32.exe as part of their mechanisms
Other platforms for T1218.011
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 1Rundll32 LSASS Dump via comsvcs.dll MiniDump
Expected signal: Sysmon Event ID 1: powershell.exe then rundll32.exe with comsvcs.dll and MiniDump in command line. Sysmon Event ID 10 (Process Access): rundll32.exe accessing lsass.exe. Sysmon Event ID 11: lsass.dmp file created in Temp. Windows Defender will likely block this on patched systems.
- Test 2Rundll32 JavaScript Execution via mshtml
Expected signal: Sysmon Event ID 1: rundll32.exe with javascript: and mshtml in command line. If WScript.Shell successfully runs calc.exe, a child process creation event for calc.exe with ParentImage=rundll32.exe will appear.
- Test 3Rundll32 DLL Execution from Temp Directory
Expected signal: Sysmon Event ID 11: DLL written to Temp. Sysmon Event ID 1: rundll32.exe with ordinal (#1) and Temp path. Sysmon Event ID 7: DLL loaded by rundll32.exe. Security Event ID 4688.
References (6)
- https://attack.mitre.org/techniques/T1218/011/
- https://lolbas-project.github.io/lolbas/Binaries/Rundll32/
- https://www.carbonblack.com/2016/04/28/threat-advisory-squiblydoo-continues-trend-of-attackers-using-native-os-tools-to-live-off-the-land/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.011/T1218.011.md
- https://blog.f-secure.com/hunting-for-the-undefined-behavior-the-case-of-comsvcs-dll/
- https://www.elastic.co/blog/hunting-for-persistence-using-elastic-security
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